arises. In addition, the conventional hybrid approach is adversely affected by the same operating condition variations that adversely affect operation of other conventional indirect wideband modulation schemes.
SUMMARY OF THE INVENTION
According to the methods and apparatus taught herein, one embodiment of modulating a signal by a frequency synthesizer comprises directly modulating a signal input to a voltage controlled oscillator (VCO) associated with the frequency synthesizer. The modulation signal has a bandwidth greater than a closed-loop bandwidth of the frequency synthesizer. The modulation signal is suppressed from a feedback path of the frequency synthesizer.
Of course, the present invention is not limited to the above features and advantages. Those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of one embodiment of a wireless communication device including a frequency synthesizer.
FIG. 2 is a block diagram of one embodiment of a frequency synthesizer.
FIG. 3 is a logic flow diagram of one embodiment of program logic for modulating a signal by a frequency synthesizer.
FIG. 4 is a block diagram of one embodiment of a modulation suppressor included in or associated with the frequency synthesizer of FIG. 2.
FIG. 5 is a block diagram of another embodiment of a modulation suppressor included in or associated with the frequency synthesizer of FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 partially illustrates an embodiment of a wireless communication device 10 such as a portable phone, cellular phone, digital camera, portable computer, printer, audio player, etc. The wireless communication device 10 comprises a frequency synthesizer 12 included in or associated with transmit circuitry 14 for providing direct frequency modulation using a wideband modulation signal, i.e., a modulation signal having a bandwidth greater than the closed-loop bandwidth of the synthesizer 12. As such, the wireless communication device 10 may perform frequency modulation in accordance with a wireless communication protocol requiring signal modulation bandwidths greater than the closed-loop bandwidth of the frequency synthesizer 12, e.g., the IEEE 802.15 Bluetooth standard, Global System for Mobile communications (GSM) standard and IEEE 802.1 lb standard.
In more detail, the frequency synthesizer 12 has a Voltage Controlled Oscillator (VCO) 16 for generating an output signal that is in-phase with a reference signal input to the synthesizer 12. The output of the VCO 16 is fed back to another input of the synthesizer 12 in the form of a feedback signal. The synthesizer 12 compares the feedback signal and the reference signal to determine a phase or frequency difference between the two signals. Operation of the VCO 16 is adjusted by modifying a control signal input to the VCO 16, the control signal determining the VCO's operating frequency (or phase). Properly modifying the control signal input to the VCO 16 enables the VCO 16 to operate in-phase with the reference signal.
A modulator 18 included in or associated with the synthesizer 12 injects wideband frequency modulation directly into the VCO 16. In an embodiment, the control signal input to the VCO 16 is directly modulated with a wideband modulation
5 signal. Accordingly, the VCO 16 not only operates in-phase with a reference signal, its output has frequency modulations corresponding to the wideband modulation signal. Since the wideband modulation signal is present in the VCO output signal, it is initially present in the feedback signal as well.
10 A modulation suppressor 20 included in or associated with the frequency synthesizer 12 suppresses the wideband modulation signal from the feedback signal. The term "suppress" as used herein means to reduce or eliminate. By suppressing the wideband modulation signal from the feedback signal, the
15 synthesizer 12 determines the phase or frequency difference between the feedback signal and the reference signal absent appreciable contribution from the wideband modulation signal. As a result, the modulation suppressor 20 effectively prevents the closed-loop dynamics of the synthesizer 12 from
20 adversely affecting the wideband frequency modulation operations of the synthesizer 12.
During operation, the wireless communication device 10 transmits (and receives) data via one or more wireless communication links (not shown). To that end, the transmit cir
25 cuitry 14 prepares data (TX Data) for transmission, e.g., by encoding the data and/or modulating it. The modulator 18 uses the data to form a wideband modulation signal. The wideband modulation signal directly modulates the VCO 16, but is suppressed from the VCO feedback signal by the modu
30 lation suppressor 20. A power amplifier 22 amplifies the modulated output of the synthesizer 12, whichmay be optionally filtered prior to amplification. The amplified signal is provided to one or more antennae (not shown) for transmission. The wireless communication device 10 may include
35 corresponding receive circuitry (not shown) for processing received signals, e.g., by demodulating and/or decoding them. The frequency synthesizer 12 may assist in received signal demodulation, e.g., by providing one or more timing reference signals to receive circuitry. A baseband processor
40 24 included in the device 10 performs various data processing tasks including providing data to the frequency synthesizer 12 for modulation and subsequent transmission.
FIG. 2 illustrates one embodiment of the frequency synthesizer 12. According to this embodiment, the synthesizer 12
45 comprises the modulator 18, a forward path including a phase-frequency detector 26, a loop filter 28 and the VCO 16, and a feedback path including the modulation suppressor 20. For ease of description only, some operational details of the frequency synthesizer 12 are described in the continuous
50 (analog) time domain while other operational details are described in the discrete (digital) time domain. However, those skilled in the art will readily recognize that the synthesizer components may be analog, digital or some combination thereof, and thus, are not limited to any particular typeorclass
55 of circuitry. As such, the frequency synthesizer 12 may comprise all analog components, all digital components, or a combination of both. Continuous waveform signals are represented herein with either the variable (t) or (x) while discrete signals are represented with the variable (k).
60 The modulator 18 converts data (TX_DATA) received from the baseband processor 24 or other circuitry to a wideband modulation signal. In one embodiment, the modulator 18 comprises a waveform generator 30 for converting data to a discrete wideband modulation signal v(k). The modulator
65 18 may include a Digital-to-Analog Converter (DAC) 32 for converting v(k) to a continuous waveform wideband modulation signal v(x). The modulator 18 further comprises cir