US20050068073A1 - Regulated adaptive-bandwidth PLL/DLL using self-biasing current from a VCO/VCDL - Google Patents

Regulated adaptive-bandwidth PLL/DLL using self-biasing current from a VCO/VCDL Download PDF

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US20050068073A1
US20050068073A1 US10/770,435 US77043504A US2005068073A1 US 20050068073 A1 US20050068073 A1 US 20050068073A1 US 77043504 A US77043504 A US 77043504A US 2005068073 A1 US2005068073 A1 US 2005068073A1
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coupled
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gate
source
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Xudong Shi
Kun-Yung Chang
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Rambus Inc
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Rambus Inc
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Publication of US20050068073A1 publication Critical patent/US20050068073A1/en
Priority to US11/743,422 priority patent/US7365581B2/en
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/08—Details of the phase-locked loop
    • H03L7/085—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal
    • H03L7/093—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal using special filtering or amplification characteristics in the loop
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/08—Details of the phase-locked loop
    • H03L7/081—Details of the phase-locked loop provided with an additional controlled phase shifter
    • H03L7/0812—Details of the phase-locked loop provided with an additional controlled phase shifter and where no voltage or current controlled oscillator is used
    • H03L7/0816—Details of the phase-locked loop provided with an additional controlled phase shifter and where no voltage or current controlled oscillator is used the controlled phase shifter and the frequency- or phase-detection arrangement being connected to a common input
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/08—Details of the phase-locked loop
    • H03L7/085—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal
    • H03L7/089—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal the phase or frequency detector generating up-down pulses
    • H03L7/0891—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal the phase or frequency detector generating up-down pulses the up-down pulses controlling source and sink current generators, e.g. a charge pump
    • H03L7/0893—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal the phase or frequency detector generating up-down pulses the up-down pulses controlling source and sink current generators, e.g. a charge pump the up-down pulses controlling at least two source current generators or at least two sink current generators connected to different points in the loop
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00—Automatic control of frequency or phase; Synchronisation
    • H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/08—Details of the phase-locked loop
    • H03L7/10—Details of the phase-locked loop for assuring initial synchronisation or for broadening the capture range
    • H03L7/107—Details of the phase-locked loop for assuring initial synchronisation or for broadening the capture range using a variable transfer function for the loop, e.g. low pass filter having a variable bandwidth

Definitions

  • the present invention relates to a circuit tracking an input signal, and in particular, a phase locked loop (“PLL”) or delay locked loop (“DLL”) circuit.
  • PLL phase locked loop
  • DLL delay locked loop
  • a PLL or DLL (“PLL/DLL”) is an electronic circuit, which generates an output signal that has a well-controlled relationship in phase/delay and frequency to an input signal.
  • PLL/DLLs are used in numerous applications including, for example, I/O interfaces of digital integrated circuits, memory systems, processors, frequency multiplication or frequency tracking.
  • a PLL/DLL may be biased using a special bandgap bias circuit or a dedicated circuit other than the PLL/DLL.
  • a special bandgap bias circuit may increase cost, design complexity, noise and power consumption in a PLL/DLL application.
  • a PLL/DLL may be voltage self-biasing, or a voltage generated by the PLL/DLL biases circuit components of the PLL/DLL.
  • This voltage self-biasing allows for process independent PLL/DLL bandwidth tracking to achieve a relatively high input bandwidth for tracking an input signal and reduces voltage-controlled oscillator (“VCO”) or voltage-controlled delay line (“VCDL”) noise.
  • VCO voltage-controlled oscillator
  • VCDL voltage-controlled delay line
  • self-biasing allows for eliminating special bandgap bias circuits.
  • voltage biasing PLL/DLLs by distributing a voltage to various components has many disadvantages.
  • voltage biasing PLL/DLLs may not have adequate bandwidth tracking for particular applications.
  • a bias-generating device such as a metal-oxide field-effect transistor (“MOSFET”), in the various PLL/DLL components receiving the biasing voltage typically must have the same threshold voltage V T as the matching device generating the bias voltage. If the devices are not the same, mismatch is introduced.
  • a voltage bias-generating device typically must operate in a saturation region in order for a good matching. Under certain device operation conditions, such as a slow corner, voltage bias-generating devices will not be in a saturation region.
  • MOSFET metal-oxide field-effect transistor
  • FIGS. 1 a - b illustrate providing current representing frequency or delay to circuit components in a PLL or DLL, respectively, according to an embodiment of the present invention.
  • FIG. 2 is architecture of a PLL according to an embodiment of the present invention.
  • FIG. 3 is architecture of a DLL according to an embodiment of the present invention.
  • FIG. 4 is a schematic of a portion of a loop resistor shown in FIG. 2 .
  • FIG. 5 is a schematic of a portion of a voltage regulator shown in FIGS. 2 and 3 .
  • FIG. 6 is a schematic of an AMP 600 according to an embodiment of the present invention.
  • FIG. 7 is a method according to an embodiment of the present invention.
  • a PLL/DLL circuit is current self-biased using current provided from a circuit component in the PLL/DLL in embodiments of the present invention.
  • a copy of current I ld provided to a VCO or a VCDL from a voltage regulator is used to bias circuit components of a PLL/DLL in embodiments of the present invention.
  • Current I ld represents frequency or delay information of a PLL or DLL, respectively.
  • Bias current I bias which is proportional to current I ld , is provided to circuit components of the PLL/DLL, such as a charge pump, phase mixer, amplifier, clock buffer and loop resistor, from an interconnect in embodiments of the present invention.
  • FIGS. 1 a and 1 b illustrate portions of a PLL and DLL, respectively.
  • current I ld is input to VCO 100 and VCDL 110 , while copies of current I ld are provided to circuit components 102 and 103 , and circuit components 112 and 113 , respectively.
  • a circuit component of the PLL/DLL includes a bias-generating device, such as a MOSFET p-type transistor having a drain coupled to the interconnect.
  • an operational amplifier (“AMP”) in a voltage regulator includes a bias-generating device, such as a p-type transistor having a source coupled to V dd and a drain coupled to the interconnect.
  • the gate of the bias-generating device is coupled to the gate of four other p-type devices.
  • Each of the four p-type devices has a source coupled to voltage V dd .
  • the drains of the first and second p-type transistors are coupled to an output providing current I ld .
  • a negative input (“INM”) of the operational amplifier (“AMP”) in the voltage regulator is coupled to the gate of a first n-type transistor and a positive input (“INP”) of the AMP is coupled to the gate of a second n-type transistor.
  • the drains of the first and second n-type transistors are coupled to the drains of the second and third p-type transistors.
  • the sources of the first and second n-type transistors are coupled to the drain of a third n-type transistor.
  • the source of the third n-type transistor is coupled to ground and the gate is coupled to a source and gate of a fourth n-type transistor.
  • the drain of the fourth n-type transistor is coupled to the drain of the fourth p-type transistor and the source of the fourth n-type transistor is coupled to ground.
  • FIG. 2 illustrates a regulated adaptive-bandwidth PLL 200 having an interconnect (shown as dashed lines) 208 to provide a copy of current I ld provided to a VCO 206 to PLL circuit components according to an embodiment of the present invention.
  • a bias current I bias which is proportional to a copy of current I ld , is provided to PLL circuit components by way of interconnect 208 .
  • PLL 200 includes circuit components such as phase-frequency detector 201 , charge-pump (“CP”) 202 , CP 203 , a loop resistor 220 comprising AMP 204 , a voltage regulator 221 , VCO 206 , and divide-by-N 207 .
  • voltage regulator 221 includes an AMP.
  • PLL 200 includes a filter circuit component in an embodiment of the present invention.
  • VCO 206 generates an output signal on interconnect 215 , such as a clock signal CLK, responsive to an input signal, such as a clock reference signal CLKref on interconnect 210 and a Fdbk signal on interconnect 216 .
  • PLL 200 is said to be in a phase-locking mode, and the oscillation period of the output signal CLK is adjusted in a phase-locking operation to track the phase of the clock reference signal CLKref.
  • an interconnect between circuit components is represented as a single line (dashed or solid) and represents a conductive element, wire or trace for transferring a signal between circuit components.
  • a single line between circuit components in the Figures represents multiple interconnections or a bus.
  • phase-frequency detector 201 compares the input signal to the Fdbk signal and generates a phase difference signal on interconnect 211 to CPs 202 and 203 .
  • up and down signals are generated by phase-frequency detector 201 .
  • a voltage V int and charge-pump voltage V c are then generated on interconnects 212 and 213 , respectively, by CPs 202 and 203 that time-averages the phase difference signal.
  • Loop capacitance is represented by capacitance C cp1 on interconnect 212 and capacitance C cp2 on line 213 .
  • Charge-pump voltage V c is input to loop resistor 220 , the output impedance of buffer AMP 204 and in particular a negative input INM of AMP 204 , and an input of voltage regulator 221 .
  • Voltage V int is also provided to loop resistor 220 , and in particular input INP of AMP 204 .
  • AMP 204 acts as a buffer.
  • FIG. 2 illustrates an exemplary loop resistor 220 , also known as an equivalent zero resistor, and many other loop resistors may be used in alternate embodiments of the present invention.
  • a voltage regulator 221 then generates a buffered voltage V reg and current I ld on interconnect 214 to VCO 206 .
  • An output signal is provided on interconnect 215 that is connected to divide-by-N 207 , which in turn provides a Fdbk signal on interconnect 216 to phase-frequency detector 201 .
  • N equals 4 or 5 and PLL 200 is used to track a clock reference signal CLKref.
  • interconnect 208 (shown as dashed lines) provides a bias current I bias to circuit components of PLL 200 which is proportional to current I ld .
  • a copy of I ld is provided on interconnect 208 .
  • interconnect 208 includes a series of current mirrors.
  • a circuit component in PLL 200 such as AMP 204 , has a device, such as a MOSFET device, to bias the component responsive to current I ld .
  • PLL 200 is self-biasing by using a current I ld rather than a voltage from VCO 206 .
  • FIG. 3 similar to FIG. 2 , illustrates a regulated adaptive-bandwidth DLL 300 having an interconnect 308 to provide a self-bias current I bias , proportional to current I ld , to bias DLL circuit components according to an embodiment of the present invention.
  • a copy of current I ld is provided to interconnect 308 in order to bias DLL circuit components.
  • DLL 300 like PLL 200 , includes circuit components such as phase detector 301 , charge pump (“CP”) 302 , voltage regulator 221 , and VCDL 306 .
  • voltage regulator 221 includes an AMP.
  • DLL 300 includes a filter circuit component in an embodiment of the present invention.
  • VCDL 306 generates an output signal on interconnect 215 , such as a clock signal CLK, responsive to an input signal, such as a clock reference signal CLKref on interconnect 210 and a Fdbk signal on interconnect 216 .
  • DLL 300 is said to be in a locking mode, and the delay of the output signal CLK is incrementally adjusted in a delay-locking operation to track the delay of the clock reference signal CLKref.
  • Phase detector 301 compares the input signal to the Fdbk signal and generates a delay signal on interconnect 211 to CP 302 .
  • An input signal such as a clock reference signal CLKref, is also provided to VCDL 306 on interconnect 310 .
  • up and down signals are generated by phase detector 301 .
  • a voltage V int is then generated on interconnect 212 by CP 302 to voltage regulator 221 .
  • CP capacitance is represented by capacitance C cp1 on interconnect 212 .
  • a voltage regulator 221 then generates a buffered voltage V reg on interconnect 214 to VCDL 306 .
  • a copy of current I ld or current I bias is then provided to interconnect 308 in embodiments of the present invention.
  • a Fdbk signal is provided on interconnect 216 to phase detector 301 .
  • interconnect 308 (shown as dashed lines) provides a bias current I bias to circuit components of DLL 300 which is proportional to current I ld .
  • interconnect 308 is a series of current mirrors.
  • a circuit component in DLL 300 has a bias-generating device, such as a MOSFET device to bias the component responsive to current I ld .
  • DLL 300 is self-biasing by using a current I ld rather than a voltage from VCDL 306 .
  • FIG. 5 illustrates a portion of a voltage regulator 221 and in particular a schematic of a prior art AMP 500 .
  • AMP 500 illustrates an AMP used in a voltage regulator 221 of a voltage self-biasing PLL/DLL.
  • AMP 500 generates a voltage V reg at an output responsive to a charge-pump voltage V c applied to positive input INP on interconnect 213 .
  • AMP 500 includes five p-type transistors 501 - 505 having sources coupled to voltage V dd . Gates of transistors 505 and 504 are coupled. Likewise, gates of transistors 503 , 502 and 501 are coupled.
  • An n-type transistor 507 has a drain coupled to a drain of transistor 503 as well as gates of transistors 503 - 501 .
  • a gate of transistor 507 is coupled to positive input INP and receives charge-pump voltage V c .
  • a gate of n-type transistor 506 is coupled to negative input INM and an output to provide voltage V reg .
  • the drains of transistors 502 - 501 are coupled to the drain of transistor 506 .
  • N-type transistor 508 has a drain coupled to sources of transistors 507 - 508 .
  • a source of transistor 508 is coupled to ground Gnd.
  • N-type transistor 509 also has a source coupled to ground Gnd and a drain coupled to gates of transistors 509 - 508 as well as a drain of transistor 504 .
  • N-type transistor 510 has a gate coupled to an output to provide voltage V reg .
  • Transistor 510 also has a source coupled to ground Gnd and a drain coupled to a drain of transistor 505 and gates of transistor 505 - 504 .
  • FIG. 4 illustrates a schematic of a portion of a loop resistor 220 and in particular a prior art AMP 400 .
  • AMP 400 illustrates an AMP used in a loop resistor of a voltage self-biasing PLL.
  • AMP 400 is used as an AMP 204 seen in FIG. 2 .
  • Amp 400 generates a charge-pump voltage V c at an output responsive to charge pump current from charge pump 203 and a voltage V int applied to positive input INP on interconnect 212 .
  • Voltage V reg is also applied to the gate of transistor 409 .
  • AMP 400 like AMP 500 , includes four p-type transistors 401 - 404 having sources coupled to voltage V dd .
  • loop resistor 220 may include more or less transistors in alternate embodiments of the present invention in order to provide an equivalent zero resistance.
  • Gates of transistors 404 and 403 are coupled.
  • gates of transistors 402 and 401 are coupled.
  • An n-type transistor 406 has a drain coupled to a drain of transistor 402 as well as gates of transistors 402 - 401 .
  • a gate of transistor 406 is coupled to positive input INP and receives voltage V int .
  • a gate of n-type transistor 405 is coupled to negative input INM and an output of charge pump 203 to provide voltage V c .
  • N-type transistor 407 has a drain coupled to sources of transistors 406 - 405 .
  • a source of transistor 407 is coupled to ground Gnd.
  • N-type transistor 408 also has a source coupled to ground Gnd and a drain coupled to gates of transistors 408 - 407 as well as a drain of transistor 403 .
  • N-type transistor 409 has a gate coupled to voltage V reg .
  • Transistor 409 also has a source coupled to ground Gnd and a drain coupled to a drain of transistor 404 and gates of transistors 404 - 403 .
  • transistor 409 is used for tracking and responds to voltage V reg in a voltage self-biasing PLL.
  • bias-generating devices such as transistor 409 , in CP 202 , CP 203 and AMP 204 should have the same threshold voltage V T and device type as the matching device in a VCO 206 or VCDL 306 .
  • bias-generating devices should be in saturation region to keep current ratio constant in order to keep the bandwidth tracking property.
  • voltage V reg will typically be close to a supply voltage V dd in slow corner operation condition, it will be difficult to keep transistor 409 in a saturation region.
  • PLL 200 or DLL 300 bandwidth tracking depends on VCO 206 or VCDL 306 having the following properties:
  • Each PLL and DLL has certain loop characteristics. For example, ⁇ equals a loop-damping factor for a PLL.
  • W n is a loop natural frequency and W ref is a loop input or reference frequency for a PLL or DLL.
  • a charge pump current I cp and loop resistor R must have the following properties: I cp proportional (V reg ⁇ V T ) 2 (3) R proportional 1/ ⁇ (V reg ⁇ V T ) (4)
  • voltage V reg may be distributed to CP 202 , CP 203 and loop resistor 220 to achieve these properties.
  • Voltage V reg controls transistor 409 to generate bias current of AMP 404 in loop resistor 220 such that R is proportional 1/ ⁇ (V reg ⁇ V T ).
  • CP 202 and CP 203 currents are set.
  • a current I ld is distributed to circuit components in PLL 200 or DLL 300 on interconnects 208 and 308 , respectively, instead of distributing (V reg ⁇ V T ), to achieve the same ⁇ and w p /w ref constant properties.
  • equations 1-4 are expressed as: K DL proportional C LD /I ld (5) K v constant of ⁇ /C LD (6) I cp proportional I ld (7) R proportional 1/ ⁇ square root ⁇ I ld (8)
  • AMP 600 having bias-generating device 605 is used instead of AMP 500 in an embodiment of the present invention.
  • AMP 600 is used in voltage regulator 221 shown in FIGS. 2 and 3 .
  • Bias-generating device 605 is a MOSFET device, and in particular a p-type device in an embodiment of the present invention.
  • P-type transistor 605 acting as a current source, has a drain coupled to interconnect 208 and 308 , respectively, and outputs bias current I bias , which is proportional to current I ld .
  • the source of transistor 605 is coupled to voltage source V dd .
  • the gate of transistor 605 is coupled to the gates of p-type transistors 604 - 601 .
  • the sources of transistors 604 - 601 are also coupled to voltage source V dd .
  • the drains of transistors 602 - 601 are coupled to an output and a drain of n-type transistor 606 .
  • a gate of transistor 606 is also coupled to the output and input INM.
  • N-type transistor 607 has a drain coupled to the drain and the gates of transistors 603 - 602 .
  • the gate of transistor 607 is coupled to input INP to receive voltage V c .
  • N-type transistor 608 has a drain coupled to the sources of transistors 606 - 607 and a source coupled to ground Gnd.
  • a gate of transistor 608 is coupled to a gate and drain of n-type transistor 609 , which has a drain, coupled to a drain of transistor 604 and a source coupled to ground Gnd.
  • start-up logic circuit 620 is used to initialize currents at the beginning of operation or power-up of AMP 600 until normal operation. Because AMP 600 is self-biased, there may not be VCO/VCDL currents at power-up and thus AMP 600 may not operate properly without the initial currents provided by start-up logic circuit 620 .
  • FIG. 7 illustrates a method 700 according to an embodiment of the present invention.
  • steps illustrated in FIG. 7 are carried out by hardware, software or a combination thereof.
  • the circuit components illustrated in FIGS. 2, 3 and 6 carry out the steps illustrated in FIG. 7 .
  • steps that are not shown may be included in various embodiments of the present invention.
  • Method 700 begins at step 701 where a current is obtained from a circuit responsive to an input signal.
  • a current I ld is obtained from an input to VCO 206 or VCDL 306 shown in FIGS. 2 and 3 , respectively.
  • current I ld is generated in response to an input signal and Fdbk signal on interconnects 210 and 216 , respectively.
  • current I ld is generated in response to an input signal and Fdbk signal on interconnects 210 and 216 , respectively.
  • Step 702 illustrates generating a bias current in response to obtaining the current from the circuit.
  • bias current I bias is generated in response to current I ld obtained from PLL 200 or DLL 300 .
  • Step 703 illustrates providing a bias current to a circuit component.
  • bias current I bias is provided to circuit components of PLL 200 and DLL 300 by interconnects 208 and 308 as seen in FIGS. 2 and 3 , respectively.
  • a bias current I bias is provided to circuit components in PLL 200 including loop resistor 220 having AMP 204 , CP 202 and CP 203 .
  • a circuit component is then biased as illustrated by step 704 .
  • these steps repeat as long as a PLL/DLL is in an operation mode or power is supplied as illustrated by loop 705 .

Abstract

A PLL/DLL circuit is current self-biased responsive to a current Ild provided from a voltage regulator to a VCO or VCDL. Bias current Ibias, which is proportional to Ild, is provided to components of the PLL/DLL, such as a charge pump or loop resistor, from an interconnect coupled to the voltage regulator. In an embodiment of the present invention, a component of the PLL/DLL includes a bias-generating device, such as a MOSFET p-type transistor having a drain coupled to the interconnect. In an embodiment of the present invention, a voltage regulator includes an AMP having a bias-generating device, such as a p-type transistor, acting as a current source, having a source coupled to Vdd and a drain coupled to the interconnect. The gate of the bias-generating device is coupled to the gate of four other p-type devices. Each of the four p-type devices has a source coupled to Vdd. The drains of the first and second p-type transistors are coupled to an output providing Ild. A negative input of the AMP (“INM”) is coupled to the gate of a first n-type transistor and a positive input of the AMP (“INP”) is coupled to the gate of a second n-type transistor. The drains of the first and second n-type transistors are coupled to the drains of the second and third p-type transistors. The sources of the first and second n-type transistors are coupled to the drain of a third n-type transistor. The source of the third n-type transistor is coupled to ground and the gate is coupled to a fourth n-type transistor. The drain of the fourth n-type transistor is coupled to the drain of the fourth p-type transistor and the source of the fourth n-type transistor is coupled to ground.

Description

    PRIORITY CLAIM
  • The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/506,540, entitled, “REGULATED ADAPTIVE-BANDWIDTH PLL/DLL USING SELF-BIASING CURRENT FROM A VCO/VCDL”, which application was filed on Sep. 26, 2003.
    • FIELD OF THE INVENTION
  • The present invention relates to a circuit tracking an input signal, and in particular, a phase locked loop (“PLL”) or delay locked loop (“DLL”) circuit.
    • BACKGROUND OF THE RELATED ART
  • A PLL or DLL (“PLL/DLL”) is an electronic circuit, which generates an output signal that has a well-controlled relationship in phase/delay and frequency to an input signal.
  • PLL/DLLs are used in numerous applications including, for example, I/O interfaces of digital integrated circuits, memory systems, processors, frequency multiplication or frequency tracking.
  • A PLL/DLL may be biased using a special bandgap bias circuit or a dedicated circuit other than the PLL/DLL. However, using a special bandgap bias circuit may increase cost, design complexity, noise and power consumption in a PLL/DLL application.
  • Alternatively, a PLL/DLL may be voltage self-biasing, or a voltage generated by the PLL/DLL biases circuit components of the PLL/DLL. This voltage self-biasing allows for process independent PLL/DLL bandwidth tracking to achieve a relatively high input bandwidth for tracking an input signal and reduces voltage-controlled oscillator (“VCO”) or voltage-controlled delay line (“VCDL”) noise. In addition, self-biasing allows for eliminating special bandgap bias circuits.
  • However, voltage biasing PLL/DLLs by distributing a voltage to various components has many disadvantages. First, voltage biasing PLL/DLLs may not have adequate bandwidth tracking for particular applications. A bias-generating device, such as a metal-oxide field-effect transistor (“MOSFET”), in the various PLL/DLL components receiving the biasing voltage typically must have the same threshold voltage VT as the matching device generating the bias voltage. If the devices are not the same, mismatch is introduced. Also, a voltage bias-generating device typically must operate in a saturation region in order for a good matching. Under certain device operation conditions, such as a slow corner, voltage bias-generating devices will not be in a saturation region.
  • Therefore, it is desirable to provide a current self-biased PLL/DLL without the above-described disadvantages.
    • BRIEF DESCRIPTION OF THE DRAWING
  • FIGS. 1 a-b illustrate providing current representing frequency or delay to circuit components in a PLL or DLL, respectively, according to an embodiment of the present invention.
  • FIG. 2 is architecture of a PLL according to an embodiment of the present invention.
  • FIG. 3 is architecture of a DLL according to an embodiment of the present invention.
  • FIG. 4 is a schematic of a portion of a loop resistor shown in FIG. 2.
  • FIG. 5 is a schematic of a portion of a voltage regulator shown in FIGS. 2 and 3.
  • FIG. 6 is a schematic of an AMP 600 according to an embodiment of the present invention.
  • FIG. 7 is a method according to an embodiment of the present invention.
    • DETAILED DESCRIPTION
  • A PLL/DLL circuit is current self-biased using current provided from a circuit component in the PLL/DLL in embodiments of the present invention. A copy of current Ild provided to a VCO or a VCDL from a voltage regulator is used to bias circuit components of a PLL/DLL in embodiments of the present invention. Current Ild represents frequency or delay information of a PLL or DLL, respectively. Bias current Ibias, which is proportional to current Ild, is provided to circuit components of the PLL/DLL, such as a charge pump, phase mixer, amplifier, clock buffer and loop resistor, from an interconnect in embodiments of the present invention.
  • FIGS. 1 a and 1 b illustrate portions of a PLL and DLL, respectively. In particular, current Ild is input to VCO 100 and VCDL 110, while copies of current Ild are provided to circuit components 102 and 103, and circuit components 112 and 113, respectively. In an embodiment of the present invention, a circuit component of the PLL/DLL includes a bias-generating device, such as a MOSFET p-type transistor having a drain coupled to the interconnect.
  • In an embodiment of the present invention, an operational amplifier (“AMP”) in a voltage regulator includes a bias-generating device, such as a p-type transistor having a source coupled to Vdd and a drain coupled to the interconnect. The gate of the bias-generating device is coupled to the gate of four other p-type devices. Each of the four p-type devices has a source coupled to voltage Vdd. The drains of the first and second p-type transistors are coupled to an output providing current Ild. A negative input (“INM”) of the operational amplifier (“AMP”) in the voltage regulator is coupled to the gate of a first n-type transistor and a positive input (“INP”) of the AMP is coupled to the gate of a second n-type transistor. The drains of the first and second n-type transistors are coupled to the drains of the second and third p-type transistors. The sources of the first and second n-type transistors are coupled to the drain of a third n-type transistor. The source of the third n-type transistor is coupled to ground and the gate is coupled to a source and gate of a fourth n-type transistor. The drain of the fourth n-type transistor is coupled to the drain of the fourth p-type transistor and the source of the fourth n-type transistor is coupled to ground.
  • FIG. 2 illustrates a regulated adaptive-bandwidth PLL 200 having an interconnect (shown as dashed lines) 208 to provide a copy of current Ild provided to a VCO 206 to PLL circuit components according to an embodiment of the present invention. In an alternate embodiment of the present invention, a bias current Ibias, which is proportional to a copy of current Ild, is provided to PLL circuit components by way of interconnect 208.
  • PLL 200 includes circuit components such as phase-frequency detector 201, charge-pump (“CP”) 202, CP 203, a loop resistor 220 comprising AMP 204, a voltage regulator 221, VCO 206, and divide-by-N 207. In an embodiment of the present invention, voltage regulator 221 includes an AMP. As one of ordinary skill in the art would appreciate, more or less circuit components are provided in alternate embodiments of the present invention. For example, PLL 200 includes a filter circuit component in an embodiment of the present invention. VCO 206 generates an output signal on interconnect 215, such as a clock signal CLK, responsive to an input signal, such as a clock reference signal CLKref on interconnect 210 and a Fdbk signal on interconnect 216. PLL 200 is said to be in a phase-locking mode, and the oscillation period of the output signal CLK is adjusted in a phase-locking operation to track the phase of the clock reference signal CLKref.
  • In an embodiment of the present invention, an interconnect between circuit components is represented as a single line (dashed or solid) and represents a conductive element, wire or trace for transferring a signal between circuit components. In an alternate embodiment of the present invention, a single line between circuit components in the Figures represents multiple interconnections or a bus.
  • As shown in FIG. 2, phase-frequency detector 201 compares the input signal to the Fdbk signal and generates a phase difference signal on interconnect 211 to CPs 202 and 203. In particular, up and down signals are generated by phase-frequency detector 201. A voltage Vint and charge-pump voltage Vc are then generated on interconnects 212 and 213, respectively, by CPs 202 and 203 that time-averages the phase difference signal. Loop capacitance is represented by capacitance Ccp1 on interconnect 212 and capacitance Ccp2 on line 213. Charge-pump voltage Vc is input to loop resistor 220, the output impedance of buffer AMP 204 and in particular a negative input INM of AMP 204, and an input of voltage regulator 221. Voltage Vint is also provided to loop resistor 220, and in particular input INP of AMP 204. In an embodiment of the present invention, AMP 204 acts as a buffer. As one of ordinary skill in the art would appreciate, FIG. 2 illustrates an exemplary loop resistor 220, also known as an equivalent zero resistor, and many other loop resistors may be used in alternate embodiments of the present invention. A voltage regulator 221 then generates a buffered voltage Vreg and current Ild on interconnect 214 to VCO 206. An output signal is provided on interconnect 215 that is connected to divide-by-N 207, which in turn provides a Fdbk signal on interconnect 216 to phase-frequency detector 201. In an embodiment of the present invention, N equals 4 or 5 and PLL 200 is used to track a clock reference signal CLKref.
  • In an embodiment of the present invention, interconnect 208 (shown as dashed lines) provides a bias current Ibias to circuit components of PLL 200 which is proportional to current Ild. In an alternate embodiment of the present invention, a copy of Ild is provided on interconnect 208. In an embodiment of the present invention, interconnect 208 includes a series of current mirrors. In an embodiment of the present invention, a circuit component in PLL 200, such as AMP 204, has a device, such as a MOSFET device, to bias the component responsive to current Ild. Thus, PLL 200 is self-biasing by using a current Ild rather than a voltage from VCO 206.
  • FIG. 3, similar to FIG. 2, illustrates a regulated adaptive-bandwidth DLL 300 having an interconnect 308 to provide a self-bias current Ibias, proportional to current Ild, to bias DLL circuit components according to an embodiment of the present invention. In an alternate embodiment of the present invention, a copy of current Ild is provided to interconnect 308 in order to bias DLL circuit components.
  • DLL 300, like PLL 200, includes circuit components such as phase detector 301, charge pump (“CP”) 302, voltage regulator 221, and VCDL 306. In an embodiment of the present invention, voltage regulator 221 includes an AMP. As one of ordinary skill in the art would appreciate, more or less circuit components are provided in alternate embodiments of the present invention. For example, DLL 300 includes a filter circuit component in an embodiment of the present invention. VCDL 306 generates an output signal on interconnect 215, such as a clock signal CLK, responsive to an input signal, such as a clock reference signal CLKref on interconnect 210 and a Fdbk signal on interconnect 216. DLL 300 is said to be in a locking mode, and the delay of the output signal CLK is incrementally adjusted in a delay-locking operation to track the delay of the clock reference signal CLKref.
  • Phase detector 301 compares the input signal to the Fdbk signal and generates a delay signal on interconnect 211 to CP 302. An input signal, such as a clock reference signal CLKref, is also provided to VCDL 306 on interconnect 310. In particular, up and down signals are generated by phase detector 301. A voltage Vint is then generated on interconnect 212 by CP 302 to voltage regulator 221. CP capacitance is represented by capacitance Ccp1 on interconnect 212. A voltage regulator 221 then generates a buffered voltage Vreg on interconnect 214 to VCDL 306. A copy of current Ild or current Ibias is then provided to interconnect 308 in embodiments of the present invention. A Fdbk signal is provided on interconnect 216 to phase detector 301.
  • In an embodiment of the present invention, interconnect 308 (shown as dashed lines) provides a bias current Ibias to circuit components of DLL 300 which is proportional to current Ild. In an embodiment of the present invention, interconnect 308 is a series of current mirrors. In an embodiment of the present invention, a circuit component in DLL 300 has a bias-generating device, such as a MOSFET device to bias the component responsive to current Ild. Thus, DLL 300 is self-biasing by using a current Ild rather than a voltage from VCDL 306.
  • FIG. 5 illustrates a portion of a voltage regulator 221 and in particular a schematic of a prior art AMP 500. AMP 500 illustrates an AMP used in a voltage regulator 221 of a voltage self-biasing PLL/DLL. AMP 500 generates a voltage Vreg at an output responsive to a charge-pump voltage Vc applied to positive input INP on interconnect 213. AMP 500 includes five p-type transistors 501-505 having sources coupled to voltage Vdd. Gates of transistors 505 and 504 are coupled. Likewise, gates of transistors 503, 502 and 501 are coupled. An n-type transistor 507 has a drain coupled to a drain of transistor 503 as well as gates of transistors 503-501. A gate of transistor 507 is coupled to positive input INP and receives charge-pump voltage Vc. A gate of n-type transistor 506 is coupled to negative input INM and an output to provide voltage Vreg. The drains of transistors 502-501 are coupled to the drain of transistor 506. N-type transistor 508 has a drain coupled to sources of transistors 507-508. A source of transistor 508 is coupled to ground Gnd. N-type transistor 509 also has a source coupled to ground Gnd and a drain coupled to gates of transistors 509-508 as well as a drain of transistor 504. N-type transistor 510 has a gate coupled to an output to provide voltage Vreg. Transistor 510 also has a source coupled to ground Gnd and a drain coupled to a drain of transistor 505 and gates of transistor 505-504.
  • FIG. 4 illustrates a schematic of a portion of a loop resistor 220 and in particular a prior art AMP 400. AMP 400 illustrates an AMP used in a loop resistor of a voltage self-biasing PLL. In an embodiment of the present invention, AMP 400 is used as an AMP 204 seen in FIG. 2. Amp 400 generates a charge-pump voltage Vc at an output responsive to charge pump current from charge pump 203 and a voltage Vint applied to positive input INP on interconnect 212. Voltage Vreg is also applied to the gate of transistor 409.
  • AMP 400, like AMP 500, includes four p-type transistors 401-404 having sources coupled to voltage Vdd. As stated above, loop resistor 220 may include more or less transistors in alternate embodiments of the present invention in order to provide an equivalent zero resistance. Gates of transistors 404 and 403 are coupled. Likewise, gates of transistors 402 and 401 are coupled. An n-type transistor 406 has a drain coupled to a drain of transistor 402 as well as gates of transistors 402-401. A gate of transistor 406 is coupled to positive input INP and receives voltage Vint. A gate of n-type transistor 405 is coupled to negative input INM and an output of charge pump 203 to provide voltage Vc. N-type transistor 407 has a drain coupled to sources of transistors 406-405. A source of transistor 407 is coupled to ground Gnd. N-type transistor 408 also has a source coupled to ground Gnd and a drain coupled to gates of transistors 408-407 as well as a drain of transistor 403. N-type transistor 409 has a gate coupled to voltage Vreg. Transistor 409 also has a source coupled to ground Gnd and a drain coupled to a drain of transistor 404 and gates of transistors 404-403. Thus, transistor 409 is used for tracking and responds to voltage Vreg in a voltage self-biasing PLL.
  • However, using transistor 409 for tracking in a voltage self-biasing PLL/DLL has disadvantages. First, bias-generating devices, such as transistor 409, in CP 202, CP 203 and AMP 204 should have the same threshold voltage VT and device type as the matching device in a VCO 206 or VCDL 306. Second, bias-generating devices should be in saturation region to keep current ratio constant in order to keep the bandwidth tracking property. However, since voltage Vreg will typically be close to a supply voltage Vdd in slow corner operation condition, it will be difficult to keep transistor 409 in a saturation region.
  • In a preferred embodiment of the present invention, PLL 200 or DLL 300 bandwidth tracking depends on VCO 206 or VCDL 306 having the following properties:
      • TD proportional Ron×CLD,
        • where: CLD is the load capacitance of delay cell buffers in VCO 206 or VCDL 306;
        • TD is the delay of delay cell buffers in VCO 206 or VCDL 306;
        • Ron is the “on resistance” of a linear MOSFET device in the delay cell buffers in VCO 206 or VCDL 306.
          R on=1/|β×(V reg −V T)|
        • where β is the process transconductance.
          VCDL 306 gain is KDL proportional CLD/|β×(Vreg−VT)21|.  (1)
          VCO 206 gain is KV proportional β/CLD.  (2)
  • Each PLL and DLL has certain loop characteristics. For example, ξ equals a loop-damping factor for a PLL. Wn is a loop natural frequency and Wref is a loop input or reference frequency for a PLL or DLL.
  • To keep ξ and wn/wref constant over process corners (independent of PLL/DLL input signal reference frequency), a charge pump current Icp and loop resistor R must have the following properties:
    Icp proportional (Vreg−VT)2  (3)
    R proportional 1/β×(Vreg−VT)  (4)
  • In a voltage self-biasing PLL/DLL, voltage Vreg may be distributed to CP 202, CP 203 and loop resistor 220 to achieve these properties. Voltage Vreg controls transistor 409 to generate bias current of AMP 404 in loop resistor 220 such that R is proportional 1/β×(Vreg−VT). Similarly, CP 202 and CP 203 currents are set.
  • In an embodiment of the present invention, a current Ild is distributed to circuit components in PLL 200 or DLL 300 on interconnects 208 and 308, respectively, instead of distributing (Vreg−VT), to achieve the same ξ and wp/wref constant properties.
  • Thus, equations 1-4 are expressed as:
    KDL proportional CLD/Ild  (5)
    Kv constant of β/CLD  (6)
    Icp proportional Ild  (7)
    R proportional 1/{square root}Ild  (8)
      • where Ild is VCO or VCDL current.
  • Replacing AMP 500, as seen in FIG. 5, with AMP 600 as seen in FIG. 6, current distribution is implemented to solve device threshold voltage VT mis-matching between circuit components. Further, current Ild, or current Ibias, distribution can improve a MOSFET device operation range used in the various circuit components, since the circuit components do not have to have the same MOSFET device type as used in the VCO 206 or VCDL 306 cells.
  • AMP 600 having bias-generating device 605, shown in FIG. 6, is used instead of AMP 500 in an embodiment of the present invention. In an alternate embodiment of the present invention, AMP 600 is used in voltage regulator 221 shown in FIGS. 2 and 3. Bias-generating device 605 is a MOSFET device, and in particular a p-type device in an embodiment of the present invention. P-type transistor 605, acting as a current source, has a drain coupled to interconnect 208 and 308, respectively, and outputs bias current Ibias, which is proportional to current Ild. The source of transistor 605 is coupled to voltage source Vdd. The gate of transistor 605 is coupled to the gates of p-type transistors 604-601. The sources of transistors 604-601 are also coupled to voltage source Vdd. The drains of transistors 602-601 are coupled to an output and a drain of n-type transistor 606. A gate of transistor 606 is also coupled to the output and input INM. N-type transistor 607 has a drain coupled to the drain and the gates of transistors 603-602. The gate of transistor 607 is coupled to input INP to receive voltage Vc. N-type transistor 608 has a drain coupled to the sources of transistors 606-607 and a source coupled to ground Gnd. A gate of transistor 608 is coupled to a gate and drain of n-type transistor 609, which has a drain, coupled to a drain of transistor 604 and a source coupled to ground Gnd.
  • In an embodiment of the present invention, start-up logic circuit 620 is used to initialize currents at the beginning of operation or power-up of AMP 600 until normal operation. Because AMP 600 is self-biased, there may not be VCO/VCDL currents at power-up and thus AMP 600 may not operate properly without the initial currents provided by start-up logic circuit 620.
  • FIG. 7 illustrates a method 700 according to an embodiment of the present invention. In alternate embodiments of the present invention, steps illustrated in FIG. 7 are carried out by hardware, software or a combination thereof. In alternate embodiments, the circuit components illustrated in FIGS. 2, 3 and 6, carry out the steps illustrated in FIG. 7. As one of ordinary skill in the art would appreciate, other steps that are not shown may be included in various embodiments of the present invention.
  • Method 700 begins at step 701 where a current is obtained from a circuit responsive to an input signal. In an embodiment of the present invention, a current Ild is obtained from an input to VCO 206 or VCDL 306 shown in FIGS. 2 and 3, respectively. In a PLL embodiment of the present invention, current Ild is generated in response to an input signal and Fdbk signal on interconnects 210 and 216, respectively. In a DLL embodiment of the present invention, current Ild is generated in response to an input signal and Fdbk signal on interconnects 210 and 216, respectively. Step 702 illustrates generating a bias current in response to obtaining the current from the circuit. In an embodiment of the present invention, bias current Ibias is generated in response to current Ild obtained from PLL 200 or DLL 300. Step 703 illustrates providing a bias current to a circuit component. In embodiments of the present invention, bias current Ibias is provided to circuit components of PLL 200 and DLL 300 by interconnects 208 and 308 as seen in FIGS. 2 and 3, respectively. In particular, a bias current Ibias is provided to circuit components in PLL 200 including loop resistor 220 having AMP 204, CP 202 and CP 203. A circuit component is then biased as illustrated by step 704. In an embodiment of the present invention, these steps repeat as long as a PLL/DLL is in an operation mode or power is supplied as illustrated by loop 705.
  • The foregoing description of the preferred embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.

Claims (37)

1) A phase locked loop circuit, comprising:
a first circuit capable of providing a current representing frequency; and,
a second circuit, coupled to the first circuit, capable of providing a bias current responsive to the current.
2) The circuit of claim 1, wherein the current is obtained from a voltage regulator.
3) The circuit of claim 1, wherein the bias current is provided to a third circuit selected from the group consisting of a charge pump, a loop resistor, phase mixer, amplifier, clock buffer and an equivalent.
4) A delay locked loop circuit, comprising:
a first circuit capable of providing a current representing a delay; and,
a second circuit, coupled to the first circuit, capable of providing a bias current responsive to the current.
5) The circuit of claim 4, wherein the current is obtained from a voltage regulator.
6) The circuit of claim 5, wherein the bias current is provided to a third circuit selected from the group consisting of a charge pump, phase mixer, amplifier, clock buffer and an equivalent.
7) A phase locked loop circuit, comprising:
a phase-frequency detector capable of providing a phase difference signal responsive to an input signal and a feedback signal;
a first charge-pump, coupled to the phase-frequency detector, capable of providing a first voltage responsive to the phase difference signal;
a second charge pump, coupled to the phase-frequency detector, capable of providing a second voltage responsive to the phase difference signal;
a loop resistor, coupled to the first charge-pump, capable of providing a buffered voltage responsive to the first voltage,
a voltage regulator, coupled to the loop resistor and the second charge pump, capable of providing a current responsive to the buffered voltage and second voltage, wherein the voltage regulator includes a bias-generating device capable of providing a bias current;
a voltage-controlled oscillator, coupled to the voltage regulator, capable of providing the feedback signal responsive to the current; and,
an interconnect, coupled to the voltage regulator, the first charge pump, and the second charge pump, capable of providing the bias current.
8) The phase locked loop circuit of claim 7, wherein the bias-generating device in the voltage regulator is a MOSFET device.
9) The phase locked loop circuit of claim 8, wherein the MOSFET device is a first p-type transistor having a drain coupled to the interconnect and a source coupled a voltage source.
10) The phase locked loop circuit of claim 9, wherein the voltage regulator includes:
a second p-type transistor having a gate coupled to a gate of the first p-type transistor and a source coupled to the voltage source;
a third p-type transistor having a gate coupled to the second transistor gate and a source coupled to the voltage source;
a fourth p-type transistor having a gate coupled to the third transistor gate and a source coupled to the voltage source;
a fifth p-type transistor having a gate coupled to the fourth transistor gate and a source coupled to the voltage source;
a first n-type transistor having a drain coupled to a drain of the second p-type transistor, a source coupled to ground and a gate coupled to the drain of the second p-type transistor;
a second n-type transistor having a drain coupled to a drain and the respective gates of the third and fourth p-type transistors, a gate coupled to an input, and a source;
a third n-type transistor having a drain coupled to respective drains of the fourth and fifth p-type transistors, a gate coupled to an output and the respective drains of the fourth and fifth transistors, and a source; and,
a fourth n-type transistor having a drain coupled to respective sources of the second and third n-type transistors, a source coupled to ground and a gate coupled to the gate and the drain of the first n-type transistor.
11) A delay locked loop circuit, comprising:
a phase detector capable of generating a phase difference signal responsive to an input signal and a feedback signal;
a charge-pump, coupled to the phase detector, capable of generating a voltage responsive to the phase difference signal;
a voltage regulator, coupled to the charge pump, capable of providing a current responsive to the voltage, wherein the voltage regulator includes a bias-generating device capable of providing a bias current;
a voltage-controlled delay line, coupled to the voltage regulator, capable of providing the feedback signal responsive to the current; and,
an interconnect, coupled to the charge pump and the voltage regulator, capable of providing the bias current.
12) The delay locked loop circuit of claim 11, wherein the bias-generating device in the voltage regulator is a MOSFET device.
13) The delay locked loop circuit of claim 12, wherein the MOSFET device is a first p-type transistor having a drain coupled to the interconnect and a source coupled to a voltage source.
14) The delay locked loop circuit of claim 13, wherein the voltage regulator includes:
a second p-type transistor having a gate coupled to a gate of the first p-type transistor and a source coupled to the voltage source;
a third p-type transistor having a gate coupled to the second transistor gate and a source coupled to the voltage source;
a fourth p-type transistor having a gate coupled to the third transistor gate and a source coupled to the voltage source;
a fifth p-type transistor having a gate coupled to the fourth transistor gate and a source coupled to the voltage source;
a first n-type transistor having a drain coupled to a drain of the second p-type transistor, a source coupled to ground and a gate coupled to the drain of the second p-type transistor;
a second n-type transistor having a drain coupled to a drain and the respective gates of the third and fourth p-type transistors, a gate coupled to an input, and a source;
a third n-type transistor having a drain coupled to respective drains of the fourth and fifth p-type transistors, a gate coupled to an output and the respective drains of the fourth and fifth transistors, and a source; and,
a fourth n-type transistor having a drain coupled to respective sources of the second and third n-type transistors, a source coupled to ground and a gate coupled to the gate and the drain of the first n-type transistor.
15) A circuit, comprising:
a first circuit capable of providing an output signal responsive to a comparison of an input signal and a feedback signal; and,
a second circuit, coupled to the first circuit, capable of providing a bias current to the first circuit responsive to the input signal.
16) The circuit of claim 15, wherein the first circuit includes a first circuit component that is biased responsive to the bias current.
17) The circuit of claim 15, wherein the first circuit component includes a loop resistor.
18) The circuit of claim 15, wherein the first circuit component includes a charge-pump.
19) The circuit of claim 15, wherein the second circuit includes a bias-generating MOSFET device.
20) The circuit of claim 19, wherein the MOSFET device is a p-type device.
21) The circuit of claim 15, wherein the first circuit is a PLL circuit.
22) The circuit of claim 15, wherein the first circuit is a DLL circuit.
23) The circuit of claim 15, wherein the first circuit includes a voltage-controlled oscillator having an input, and the second circuit is capable of generating the bias current proportional to input current provided to the voltage-controlled oscillator input.
24) A circuit, comprising:
a first p-type device having a gate, a drain capable of outputting a current proportional to an output current and a source coupled to a voltage source;
a second p-type transistor having a gate coupled to the gate of the first p-type transistor and a source coupled to the voltage source;
a third p-type transistor having a gate coupled to the gate of the second transistor and a source coupled to the voltage source;
a fourth p-type transistor having a gate coupled to the gate of the third transistor and a source coupled to the voltage source;
a fifth p-type transistor having a gate coupled to the gate of the fourth transistor and a source coupled to the voltage source;
a first n-type transistor having a drain coupled to a drain of the second p-type transistor, a source coupled to ground and a gate coupled to the drain of the second p-type transistor;
a second n-type transistor having a drain coupled to a drain of the third p-type transistor, a gate coupled to an input and respective gates of the third and fourth p-type transistors, and a source;
a third n-type transistor having a drain coupled to respective drains of the fourth and fifth p-type transistors, a gate coupled to an output and the respective drains of the fourth and fifth p-type transistors, and a source; and,
a fourth n-type transistor having a drain coupled to respective sources of the second and third n-type transistor, a source coupled to ground and a gate coupled to a gate of the first n-type transistor.
25) The circuit of claim 24, wherein the circuit is included in an operational amplifier capable of generating a buffered signal at the output responsive to a signal at the input.
26) A method, comprising:
obtaining a current from a circuit responsive to an input signal;
providing a bias current to a circuit component in the circuit responsive to the current; and,
biasing the circuit component responsive to the bias current.
27) The method of claim 26, wherein the circuit is a PLL.
28) The method of claim 26, wherein the circuit is a DLL.
29) The method of claim 26, wherein the input signal is a clock reference signal.
30) The method of claim 26, wherein the circuit component is a loop resistor.
31) The method of claim 26, wherein the circuit component is a charge-pump.
32) The method of claim 26, wherein the circuit component is a phase mixer.
33) The method of claim 26, wherein the circuit component is an amplifier.
34) The method of claim 26, wherein the circuit component is a clock buffer.
35) A method, comprising:
obtaining a current representing frequency from a voltage regulator in a phase locked loop circuit; and,
providing a bias current to a circuit component in the phase locked loop circuit responsive to the current.
36) A method, comprising:
obtaining a current representing delay from a voltage regulator in a delay locked loop circuit; and,
providing a bias current to a circuit component in the delay locked loop circuit responsive to the current.
37) A circuit, comprising:
a first circuit capable of providing an output signal responsive to a comparison of an input signal and the output signal, wherein the first circuit includes a circuit component; and,
means, coupled to the first circuit, for providing a bias current to the circuit component responsive to the input signal.
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