WO2002001734A2 - Wireless transceiver with subtractive filter compensating both transmit and receive artifacts - Google Patents
Wireless transceiver with subtractive filter compensating both transmit and receive artifacts Download PDFInfo
- Publication number
- WO2002001734A2 WO2002001734A2 PCT/US2001/017754 US0117754W WO0201734A2 WO 2002001734 A2 WO2002001734 A2 WO 2002001734A2 US 0117754 W US0117754 W US 0117754W WO 0201734 A2 WO0201734 A2 WO 0201734A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- signal
- filter
- circuit
- receive
- transmit
- Prior art date
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
- H04B1/40—Circuits
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
- H04B1/40—Circuits
- H04B1/50—Circuits using different frequencies for the two directions of communication
- H04B1/52—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa
- H04B1/525—Hybrid arrangements, i.e. arrangements for transition from single-path two-direction transmission to single-direction transmission on each of two paths or vice versa with means for reducing leakage of transmitter signal into the receiver
Definitions
- the invention relates to wireless data transceivers. More particularly, the invention relates to wireless data and voice transceivers with full duplex functionality provided by frequency division multiplexing .
- Cordless and cellular phones are designed to carry voice modulation of adequate quality for distances from a few hundred feet up to a few miles for cell phones. It is desirable to provide phones that accomplish this while being low cost, having adequate battery life and meeting regulatory requirements on radio emis- sions .
- the use of direct transmit and single conversion receive is one of the simplest architectures with a single local oscillator that meets these goals.
- U.S. Patent Nos . 5,493,583; 5,533,056; and 5,550,865 to Cripps and U.S. Patent No. 5,444,737 to Cripps et al . describe a direct transmit, single conversion receive architecture in a wireless data transceiver.
- the wireless data transceiver functions for transmitting and receiving frequency modulated (FM) signals.
- the transceiver has a single oscillator which serves as both the radio frequency source for the transmitter and the local oscillator signal source for the receiver. During signal transmission, the oscillator output is frequency modulated to provide an FM transmit signal to the transmit antenna.
- the oscillator output is frequency modulated by modulating an error feedback signal which serves as the control voltage for a voltage controlled oscillator in a phase lock loop circuit, thereby producing the FM transmit signal .
- the oscillator output in the form of the transmitted FM signal, is received via the receive antenna along with an FM receive signal for mixing therewith to down-convert the FM receive signal.
- the binary transmit data is subtracted out.
- a directly modulated local oscillator for both transmit and receive can present a problem.
- this same local oscillator is also used to down- convert the receive signal to some convenient intermediate frequency (IF) for filtering and amplification.
- IF intermediate frequency
- the modulation signal used for transmitting also appears in the receive signal, and is detected.
- the user hears his own voice as a one hundred percent echo, that is, at the same volume as the far end detected signal. This large radio echo is not acceptable to the users.
- the above object has been achieved by a wireless transceiver which uses compensating filtering to negate filter artifacts affecting the transmit echo signal, so it can be more accurately subtracted.
- the compensator is a filter and optionally an amplitude compensator which approximately duplicates the filtering effects of the phase lock loop circuitry on a modulated VCO on the transmit side of the transceiver and the effects of IF filtering on the receive side which would delay and distort the receive signal. Then, the compensator signal is added or subtracted, depending on phase, from the receive signal at the baseband audio level so that the receive signal is free from transmit echo artifacts. In the absence of the compensation filter, the subtraction of the transmit echo is much less effective, or almost absent in some cases .
- the utility of the transceiver of the present invention has nearly the minimum RF circuitry which can satisfy most governmental (FCC) requirements for cordless telephones, while having good audio quality.
- FCC governmental
- Fig. 1 is a block diagram of a wireless transceiver of the present invention.
- Fig. 2 is a diagram illustrating the frequency response of circuits in the transmit and receive sides of the transceiver of Fig. 1.
- Fig. 3 is an electrical schematic diagram of a compensating filter circuit used in the transceiver of Fig. 1.
- Fig. 4 is a graph of gain vs. frequency for the compensating filter circuit of Fig. 3.
- a wireless trans- ceiver of the present invention is seen to have a receive side 13 and a transmit side 15.
- An antenna 11 is used to both transmit modulated radio frequency (RF) signals and to receive modulated RF signals .
- the receive signal 70 proceeds to the receiver side 13 consisting of an RF amplifier which incorporates a base receive RF filter 21, then to a dow -conversion mixer 23, an intermediate frequency (IF) amplifier and filter 25, an FM detector 27, a subtractor 29 and a receive audio processor 20.
- RF radio frequency
- the outgoing signals that are transmitted through antenna 11 are generated from the transmitter side 15 which is a direct FM or phase modulated transmitter consisting of a transmit audio processor 30, a phase lock loop circuit including a voltage controlled oscillator (VCO) 35, a phase lock loop synthesizer 37 and a reference oscillator 39, a transmit buffer amplifier 33 and a transmit harmonic filter 31.
- a compensating filter 17 is connected between the transmitter circuit 15 and the receiver circuit 13. The compensating filter 17 compensates for frequency distortion in the demodulator of the receive circuit 13 and also for such distortion of the transmit modulation as may occur in the VCO 35 and synthesizer 37 of the phase lock loop circuit and will be described in more detail below. Additionally, an amplitude compensator 80 is also connected between the compensating filter 17 and the receiver circuit 13.
- the amplitude compensator 80 compensates for amplitude distortion in the demodulator of the receiver circuit 13.
- a microcontroller 40 interfaces with the audio processors of the transceiver, as well as with keyboards, indicator lights, and other peripheral devices, to provide the function of process control.
- the RF filter 21 is a wide band filter acting on the receive signal 70 to reduce incoming signal noise, spurious signals and to reduce the power in the transmitter signal which reaches the receiver.
- the filtered signal 71 proceeds to a down-conversion mixer 23 where the output signal from VCO 35 is mixed with the RF signal from RF filter 21 to produce the intermediate frequency (IF) signal.
- the IF signal 72 is amplified by IF amplifier/filter 25 and the amplified signal 73 proceeds to a FM detector 27, or alternatively a phase demodulator in the case of phase modulation, which demodulates the IF signal.
- the IF filter is typically a narrow band filter having a significant effect on the IF signal. Therefore, the IF filter is modeled and taken into account in the compensating filter of the present invention, but the RF filter, having a smaller distortion effect is not modeled or taken into account .
- the demodulator has a characteristic filter function which may also be modeled, taking into account frequency and amplitude distortion.
- the demodulated signal 74 proceeds to a subtractor circuit 29, in which the demodulated signal 74 is summed differentially with the signal 75 from the compensating filter 17.
- the objective of the subtractor circuit 29 is to remove the transmit modulation from the receive signal, so one must pay attention to phasing as well as frequency response. For example, if the local oscillator 35 has its frequency increased when the transmit modulation voltage increases, and then the down-conversion mixer 23 has the local oscillator lower in frequency than the receive signal, then the mixer 23 inverts the local oscillator 35 frequency at its output 72. Therefore, when the transmit modulation increases then the IF frequency 72 and 73 decreases. Next, the phasing of the FM Detector 27 must be considered.
- the difference signal 76 then proceeds to the receive audio processor 20.
- the audio processor generally includes a compandor circuit, which improves the signal-to-noise ratio by compressing the volume range of the voice signal at transmitter by means of a compressor, and restores the normal range at the receiving end with an expander.
- the voice signal will typically also be fil- tered, to prevent undesirable modulation frequency range in transmit, and limited to prevent excessive modulation level in transmit.
- the receive audio will typically be filtered to eliminate noise lying outside the voice fre- quency range. It may also include gain or volume control. For data, typically no audio processor is used, or a much simpler one than for voice. If the voice signal has been digitized by a vocoder, then typically the audio processor will consist simply of pulse shaping filters in transmit and noise-bandwidth control filters in receive.
- the base receive RF filter 21, down-converter mixer 23, IF amplifier/ filter 25, FM detector 27 and subtractor circuit 29 can all be implemented in a conventional manner as is known in the art.
- the receive audio processor 20 can be implemented by any of a number of audio processors as may be suitable for the analog or digital signal.
- the analog voice or digital data signal 68 proceeds to a transmit audio processor 30 which processes the transmit modulation into a transmit baseband signal 67 which is input into the compensating filter 17 and also into the voltage controlled oscillator 35.
- the phase lock loop synthesizer 37 has an input 66 from a stable reference oscillator 39 and a feedback input 65 from the voltage controlled oscillator 35. If there is no input signal to the system, the error voltage is the value required for phaselock. Then, the voltage controlled oscillator (VCO) 35 operates at a carrier frequency, fo . When the trans- mit modulation signal 67 is applied, the VCO frequency control output signal 62 is modulated, but filtered by the phase lock loop 37.
- the PLL attenuates the swing with a filter characteristic that can be modeled with known programs, but the VCO is nevertheless modulated outside of the loop bandwidth. Inside the PLL bandwidth, the modulation is reduced. It is this RF signal 62 that is transmitted via the trans- mitter antenna. The frequency modulated RF signal 62 proceeds through an output buffer amplifier 33 and a harmonic filter 31 before proceeding to the antenna 11 for transmission.
- the compo- nent blocks of the transmitter circuit 15 such as the
- VCO 35 the phase lock loop synthesizer 37, the reference oscillator 39, and the buffer amplifier 33 and harmonic filter 31 can all be implemented in a conventional manner as is known in the prior art.
- the transmit audio proces- sor 30, can be the same type of processor as described above with reference to the receive audio processor 20, typically consisting of a compressor, a clipper and a filter for analog voice applications.
- the compensating filter 17 is connected between the transmit audio processor 30 of the transmitter circuit 15 and the subtractor 29 of the receiver circuit 13.
- the compensating filter 17 serves to modify the frequency and phase spectrum of transmit modulation 67 so that it will be a good match to the receive signal 74 component of transmit modulation, thus allowing this signal to be accurately removed to give an uncontaminated receive signal 76.
- a typical phase lock loop circuit has a bandwidth of about 150 Hz and a phase lock loop lead of zero at 10 Hz. These values would incorporate a well damped phase lock loop circuit.
- the receiver also has some filtering, mainly in the IF amplifier/filter, and this has an effect on the audio signal.
- the compensating filter would need to compensate the modulation signal before it reaches the subtractor so that the output signal from the subtractor is correct.
- the compensating filter 17 must compensate for both the effects of phase lock loop circuit in the transmitter circuit 15 and the effects of the filtering in the receiver circuit 25.
- the filtering effects of the RF filter 13 on the baseband receive are unimportant because the RF filter is quite wide compared to the baseband signal bandwidth.
- the phase lock loop circuit may have a single highpass effect below 150 Hz, and a double highpass effect below 10Hz. This is represented in Fig. 2 by a pair of highpass filters 83 and 84 in the transmitter circuit 15. Also, as discussed above, the IF filtering in the receiver circuit may have the effect of lowpassing the audio signal with a two pole response at 10 KHz. This is represented in Fig. 2 by a pair of lowpass filters 81, 82 in the receiver circuit 13.
- the compensating filter 17 In order to achieve a pure receive signal 76 at the output of the subtractor 29, the compensating filter 17 must compensate for both the highpass effects of the transmitter circuit 15 and the lowpass effects of the receiver circuit 25.
- the compensating filter circuit 17 is shown to include two highpass filters 85 and 86 and two lowpass filters 87 and 88.
- the number of highpass and lowpass effects described in conjunction with Fig. 2 is merely exemplary and the precise compensating filter characteristic is determined by modeling the PLL filter effect on the VCO output signal 62 combined with the IF filter effect on the mixer output signal 72.
- the compensating filter is the same as this composite.
- the various subcircuits of the transmitter and receiver circuits may have other filter effects which may be modeled and matched by the compensating filter circuit .
- the input node 51 receives the transmit audio signal from the transmit audio processor of the transmitting circuit.
- a resistor Rl and capacitor Cl are connected in series to input node 51.
- a resistor R2 is connected between one end of capacitor Cl and ground.
- a capacitor C2 is connected in parallel with resistor R2 between the end of capacitor Cl and ground.
- Capacitor C3 is connected after resistor R2 and capacitor C2 , in series between capacitor Cl and a resistor R3.
- the second end of resistor R3 is connected to the negative input terminal Nl of operational amplifier 60.
- the positive input terminal N3 of operational amplifier 60 is connected to ground.
- Resistor R4 and capacitor C4 are connected in parallel between negative input terminal Nl and the output terminal N2 of operational amplifier 60.
- the output terminal N2 is connected to the output node 52 of the compensating filter circuit.
- the output node 52 of the compensating filter circuit 17 is connected to the subtractor of the receive circuit of the transceiver.
- a typical phase lock loop has a bandwidth of about 150 Hz
- capacitor Cl having a value of 22 nF
- capacitor C3 having a capacitance of 22 nF
- forms a second highpass filter 55 with resistor R3 which has a resistance of 100 K ⁇ .
- the receive side also has some filtering, mainly in the IF stage, and this has an effect on the audio signal.
- resistor Rl having a resistance of 10 K ⁇
- capacitor C2 which has a capacitance of 1.5 nF.
- resis- tor R4 having a resistance of 100 K ⁇
- capacitor C4 having a capacitance of 150 pF
- the two lowpass filters have the effect of matching the effects of any significant IF filtering from the receive circuit, while the highpass filters 53 and 55 have the effect of matching any effects of the phase lock loop circuit in the transmit audio.
- a graph of the effects of the compensating filtering is shown.
- the graph illustrates the signal gain in decibels (dB) on the Y axis 92 and the frequency (Hz) on a logarithmic scale on the X axis 91.
- a portion of a graph 94 between 10 and 150 Hz there is a 20 dB per decade highpass slope. This is due to the effects of the highpass filter 55.
- the portion of the graph 93 below 10 Hz there is a slope of 40 dB per decade highpass slope, which is due to the combination of the highpass filters 53 and 55.
- the portion of the graph 95 above 150 Hz is shown to have a slope of 0 dB until the frequency reaches 10 KHz in which the two pole response from the IF filtering needs to be compensated.
- Various implementations of the compensating filter and amplitude compensator can be constructed based upon well known engineering models of filters. Such models are used to combine the filtering effects of the phase lock loop circuitry on the transmit side and the receive side IF filtering, as well as amplitude distortion in the detector circuit.
Abstract
Description
Claims
Priority Applications (6)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CA002402428A CA2402428A1 (en) | 2000-06-26 | 2001-05-31 | Wireless transceiver with subtractive filter compensating both transmit and receive artifacts |
DE60110588T DE60110588T2 (en) | 2000-06-26 | 2001-05-31 | WIRELESS TRANSMITTER RECEIVER WITH SUBTRACTIVE FILTER FOR COMPENSATION OF SENT AND RECEIVED ARTEFACTS |
EP01944216A EP1295404B1 (en) | 2000-06-26 | 2001-05-31 | Wireless transceiver with subtractive filter compensating both transmit and receive artifacts |
AU2001266651A AU2001266651A1 (en) | 2000-06-26 | 2001-05-31 | Wireless transceiver with subtractive filter compensating both transmit and receive artifacts |
JP2002505769A JP2004502377A (en) | 2000-06-26 | 2001-05-31 | Wireless transceiver with subtraction filter to compensate for both transmit and receive errors |
NO20026060A NO20026060L (en) | 2000-06-26 | 2002-12-17 | Wireless transceiver with subtractive filter that compensates for both sending and receiving artifacts |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/603,801 | 2000-06-26 | ||
US09/603,801 US6735181B1 (en) | 2000-06-26 | 2000-06-26 | Wireless transceiver with subtractive filter compensating both transmit and receive artifacts |
Publications (2)
Publication Number | Publication Date |
---|---|
WO2002001734A2 true WO2002001734A2 (en) | 2002-01-03 |
WO2002001734A3 WO2002001734A3 (en) | 2002-06-13 |
Family
ID=24416977
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US2001/017754 WO2002001734A2 (en) | 2000-06-26 | 2001-05-31 | Wireless transceiver with subtractive filter compensating both transmit and receive artifacts |
Country Status (11)
Country | Link |
---|---|
US (1) | US6735181B1 (en) |
EP (1) | EP1295404B1 (en) |
JP (1) | JP2004502377A (en) |
KR (1) | KR20030010743A (en) |
CN (1) | CN1217493C (en) |
AU (1) | AU2001266651A1 (en) |
CA (1) | CA2402428A1 (en) |
DE (1) | DE60110588T2 (en) |
NO (1) | NO20026060L (en) |
TW (1) | TW517480B (en) |
WO (1) | WO2002001734A2 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN100384268C (en) * | 2003-07-26 | 2008-04-23 | 华为技术有限公司 | A transceiver singleboard |
Families Citing this family (14)
Publication number | Priority date | Publication date | Assignee | Title |
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US7206366B2 (en) * | 2002-08-07 | 2007-04-17 | Broadcom Corporation | System and method for programmably adjusting gain and frequency response in a 10-GigaBit ethernet/fibre channel system |
US6914489B2 (en) * | 2002-09-26 | 2005-07-05 | Koninklijke Philips Electronics N.V. | Voltage-controlled oscillator presetting circuit |
JP4298468B2 (en) * | 2003-10-31 | 2009-07-22 | シャープ株式会社 | Frequency conversion circuit, radio frequency receiver, and radio frequency transceiver |
TWI311423B (en) * | 2004-11-03 | 2009-06-21 | Wionics Researc | Transceiver for use in an ultrawideband communication system |
US7400865B2 (en) * | 2005-02-09 | 2008-07-15 | Nokia Corporation | Variable bandwidth envelope modulator for use with envelope elimination and restoration transmitter architecture and method |
US20060280270A1 (en) * | 2005-05-26 | 2006-12-14 | Brima Ibrahim | Method and system for FM communication |
KR100771789B1 (en) * | 2005-08-04 | 2007-10-30 | 삼성전기주식회사 | Television receiver with video signal distortion compensation |
US20090098834A1 (en) * | 2006-03-07 | 2009-04-16 | Matsushita Electric Industrial Co., Ltd. | Frequency synthesizer, radio communication system, and semiconductor device |
US8300157B2 (en) * | 2007-11-06 | 2012-10-30 | Himax Technologies Limited | Method for estimating frequency offsets and frequency offset estimation circuit thereof |
CN101547011B (en) * | 2008-03-25 | 2013-06-26 | 瑞昱半导体股份有限公司 | Communication device with adjustable compensation filter and method thereof |
US8626090B2 (en) * | 2010-03-23 | 2014-01-07 | Telefonaktiebolaget Lm Ericsson (Publ) | Circuit and method for interference reduction |
JP5236711B2 (en) * | 2010-09-30 | 2013-07-17 | 株式会社エヌ・ティ・ティ・ドコモ | Mobile communication terminal, multi-frequency simultaneous communication method |
CN102420576A (en) * | 2011-11-21 | 2012-04-18 | 上海大亚科技有限公司 | Audio operational amplification circuit structure and audio output circuit structure |
GB2505684A (en) * | 2012-09-07 | 2014-03-12 | Enmodus Ltd | Cancellation of transmitter leakage in a transceiver using a predetermined phase relationship between transmit and receive carriers |
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US3931575A (en) * | 1974-10-21 | 1976-01-06 | United Technologies Corporation | Filter stabilized single oscillator transceivers |
US3935533A (en) * | 1973-03-02 | 1976-01-27 | United Technologies Corporation | Single oscillator microwave transceiver |
WO1985002734A1 (en) * | 1983-12-05 | 1985-06-20 | Motorola, Inc. | Duplex communication transceiver with modulation cancellation |
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JPS5915416B2 (en) * | 1980-09-24 | 1984-04-09 | 日本電信電話株式会社 | mobile radio |
US5550865A (en) | 1993-05-05 | 1996-08-27 | National Semiconductor Corporation | Frequency modulator for data transceiver |
US5444737A (en) | 1993-05-05 | 1995-08-22 | National Semiconductor Corporation | Wireless data transceiver |
US5603113A (en) * | 1993-06-16 | 1997-02-11 | Oki Telecom | Automatic gain control circuit for both receiver and transmitter adjustable amplifiers including a linear signal level detector with DC blocking, DC adding, and AC removing components |
NO305499B1 (en) * | 1996-11-06 | 1999-06-07 | Nera Asa | Downconversion system and method in which the received signal is downconverted |
US6308048B1 (en) * | 1997-11-19 | 2001-10-23 | Ericsson Inc. | Simplified reference frequency distribution in a mobile phone |
-
2000
- 2000-06-26 US US09/603,801 patent/US6735181B1/en not_active Expired - Lifetime
-
2001
- 2001-05-31 KR KR1020027017263A patent/KR20030010743A/en not_active Application Discontinuation
- 2001-05-31 EP EP01944216A patent/EP1295404B1/en not_active Expired - Lifetime
- 2001-05-31 CA CA002402428A patent/CA2402428A1/en not_active Abandoned
- 2001-05-31 DE DE60110588T patent/DE60110588T2/en not_active Expired - Fee Related
- 2001-05-31 JP JP2002505769A patent/JP2004502377A/en active Pending
- 2001-05-31 AU AU2001266651A patent/AU2001266651A1/en not_active Abandoned
- 2001-05-31 WO PCT/US2001/017754 patent/WO2002001734A2/en active IP Right Grant
- 2001-05-31 CN CN018116418A patent/CN1217493C/en not_active Expired - Fee Related
- 2001-06-20 TW TW090114941A patent/TW517480B/en not_active IP Right Cessation
-
2002
- 2002-12-17 NO NO20026060A patent/NO20026060L/en not_active Application Discontinuation
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
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US3935533A (en) * | 1973-03-02 | 1976-01-27 | United Technologies Corporation | Single oscillator microwave transceiver |
US3931575A (en) * | 1974-10-21 | 1976-01-06 | United Technologies Corporation | Filter stabilized single oscillator transceivers |
WO1985002734A1 (en) * | 1983-12-05 | 1985-06-20 | Motorola, Inc. | Duplex communication transceiver with modulation cancellation |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN100384268C (en) * | 2003-07-26 | 2008-04-23 | 华为技术有限公司 | A transceiver singleboard |
Also Published As
Publication number | Publication date |
---|---|
NO20026060L (en) | 2003-02-26 |
DE60110588T2 (en) | 2006-02-23 |
KR20030010743A (en) | 2003-02-05 |
DE60110588D1 (en) | 2005-06-09 |
EP1295404B1 (en) | 2005-05-04 |
CA2402428A1 (en) | 2002-01-03 |
US6735181B1 (en) | 2004-05-11 |
CN1217493C (en) | 2005-08-31 |
EP1295404A2 (en) | 2003-03-26 |
JP2004502377A (en) | 2004-01-22 |
NO20026060D0 (en) | 2002-12-17 |
AU2001266651A1 (en) | 2002-01-08 |
WO2002001734A3 (en) | 2002-06-13 |
TW517480B (en) | 2003-01-11 |
CN1437797A (en) | 2003-08-20 |
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