JP2006054547A - Optimizing method of receiving apparatus and receiving characteristic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a secondary distortion without using a filter, such as an RFSAW, etc., for converting a high frequency signal. <P>SOLUTION: In a receiving apparatus which receives a digitally modulated signal, the circuit bias of a low noise amplifier 3, mixers 4, 5, the whole balancing is maintained by correcting the circuit part bias of a low noise amplifier 3, mixers 4, 5, a local buffer 10, etc., and secondary distortion jamming is suppressed. Since the secondary distortion jamming appears as the deterioration of an S/N ratio in a demodulator, this S/N ratio is detected, and a bias is corrected so that the S/N ratio may become the maximum. Consequently, the secondary distortion jamming is suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a modulation technique for a wireless communication apparatus that transmits and receives a digitally modulated signal, and more particularly to a technique that is effective when applied to frequency conversion by a direct conversion method in a receiving apparatus.

  Mobile phones are expanding the market worldwide as wireless communication devices that transmit and receive digitally modulated signals, and various modulation schemes have been proposed and put into practical use.

  In particular, the GSM system used mainly in Europe and the like is not limited to the 900 MHz band (GSM900) in which the transmission and reception bands are 880 to 915 MHz and 935 to 960 MHz, respectively, and the DCS (transmission and reception band is 1710 to 1785 MHz, respectively) A 1.8 GHz band (DCS1800) of 1805 to 1880 MHz and a PCS (1.9 GHz band (PCS1900) having transmission and reception bands of 1850 to 1910 MHz and 1930 to 1990 MHz, respectively, are defined.

  In Japan, the WCDMA system (2 GHz band (WCDMA2000) with transmission and reception bands of 1920-1980 MHz and 2110-2170 MHz, respectively) was started as the third generation system.

  The GSM transmission / reception circuit is “A Single-Chip Quad-Band Direct-Conversion GSM / GPRS RF Transceiver With Integrated VCOs and Fractional-N Synthesizer”. CONTROL CIRCUIT "(see Patent Document 1).

In these documents, as a frequency conversion method, a direct conversion method for directly converting a received RF (high frequency) signal amplified by an LNA (low noise amplifier) into an IQ signal in the baseband is used. The direct conversion method eliminates the need for the intermediate frequency filter required in the heterodyne method and is effective in reducing the number of components and the mounting area, and is expected to be applied not only to the GSM method but also to the WCDMA method in the future.
ISSCC 2004, 14, 2 US Pat. No. 5,483,691

  However, the present inventors have found that the frequency conversion technique using the direct conversion method as described above has the following problems.

  That is, the direct conversion method has the advantages as described in the background art, but it is important to reduce the second-order distortion because the received signal is directly converted to the baseband.

  In particular, since the WCDMA system is a simultaneous transmission / reception operation, a transmission signal having a maximum of +20 dBm or more becomes an interference wave and jumps into the reception unit, which is directly converted into a baseband and becomes an interference.

  Reduction of secondary distortion can improve performance by making the circuit a balanced configuration, but completely balances the RF-IC, which is a semiconductor device for high-frequency processing, including element manufacturing variations and layout. It is difficult.

  Therefore, the direct conversion RF-IC for WCDMA that is currently in practical use is a technique for suppressing the generation of secondary distortion by suppressing the transmission signal using an RF SAW (Surface Acoustic Wave) filter between the LNA and the mixer. Therefore, it is considered that the number of parts and the mounting area are increased.

  An object of the present invention is to provide a technique for significantly reducing second-order distortion without using a filter such as RFSAW when converting a high-frequency signal.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

  The present invention is a receiving device including an analog signal processing unit that receives a high-frequency signal and converts the frequency, and a signal demodulation unit that demodulates the received signal, and the demodulated signal has a maximum SN (Signal to Noise) ratio. In this way, bias correcting means for correcting the bias of the analog signal processing unit is provided.

  Further, the present invention is a receiving apparatus including an analog signal processing unit that receives a high-frequency signal and converts the frequency, and a signal demodulation unit that demodulates the received signal, and a distortion component generated in the analog signal processing unit is Bias correcting means for correcting the bias of the analog signal processing unit so as to be minimized is provided.

  Furthermore, the outline | summary of another invention is shown briefly.

  The present invention relates to a method for optimizing reception characteristics when receiving a high frequency signal and performing frequency conversion, and detects a demodulated signal in a signal demodulating unit so that the S / N ratio of the demodulated signal is maximized. It controls the bias of the processing unit.

  The present invention is also a method for optimizing reception characteristics when receiving a high frequency signal and performing frequency conversion, and detects a second-order distortion component of a detection signal generated by an analog signal processing unit, and 2 of the detection signal. The bias of the analog signal processing unit is controlled so that the next distortion component is minimized.

  The contents of the present invention will be described in more detail as follows.

  Correcting the bias of circuit parts such as low noise amplifiers, mixers, local buffers, etc., balances the whole and suppresses secondary distortion interference. Since the secondary distortion interference is caused by degradation of the S / N ratio in the signal demodulator, the S / N ratio is detected, and the bias is corrected so that the S / N ratio becomes maximum, thereby suppressing the secondary distortion interference. Is possible.

  Furthermore, a technique may be used in which a secondary distortion interference wave is directly detected and the bias is corrected so that the interference wave is minimized. For bias correction, for example, the bias correction of the Gilbert cell of the mixer, the bias correction of the mixer input buffer, the low noise amplifier, and the bias of the base, emitter and collector of the transistors forming the differential pair of the local buffer are finely adjusted.

  Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.

  (1) The S / N ratio can be improved by detecting the S / N ratio of the I signal and the Q signal and changing the bias conditions of the low-noise amplifier, mixer, and local buffer according to the detection result.

  (2) Further, secondary distortion interference can be suppressed by correcting the bias so that the S / N ratio is maximized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

(Embodiment 1)
FIG. 1 is a block diagram of a receiving apparatus according to Embodiment 1 of the present invention, and FIG. 2 is a flowchart showing an example of an operation for optimizing the S / N ratio of a received signal in the receiving apparatus of FIG.

  In the first embodiment, the receiving device receives a digitally modulated signal and includes an antenna input terminal 1, a duplexer (DPX) 2, and a receiving system circuit 56 as shown in FIG. .

  The reception system circuit 56 includes a low noise amplifier (LNA) 3, mixers 4 and 5, a VCO (oscillation circuit) 7, amplification circuits 8 and 9, a local buffer 10 including a 90-degree phase shifter, and an analog filter (LPF) 11. 12, A / D (Analog / Digital) converters 13 and 14, digital filters (FIR) 15 and 16, a control unit 17, a detector 20, and a demodulation unit 27.

  In this reception system circuit 56, an analog processing unit is constituted by the low noise amplifier 3, the mixers 4 and 5, the VCO 7, the amplifier circuits 8 and 9, the local buffer 10, and the analog filters 11 and 12, and an A / D converter 13 and 14, the digital filters 15 and 16, the controller 17, the detector 20, and the demodulator 27 constitute a signal demodulator.

  A signal flow in the receiving apparatus will be described.

  A radio high frequency signal (hereinafter referred to as an RF signal) input from the antenna input terminal 1 is demultiplexed from the transmission signal 22 by the duplexer 2 and input to the reception system circuit 56. In the reception system, the signal is amplified by the low noise amplifier 3 and quadrature-detected by the mixers 4 and 5 using the 90 ° phase shift signals 6 and 21 output from the VCO 7 and the local buffer 10 to obtain I (In-phase) / Q (Quadrature). -Phase) signal, respectively.

  The I / Q signals are gain-controlled by gain control circuits 8 and 9, respectively, unnecessary waves are removed by analog filters 11 and 12, and then converted to digital signals by A / D converters 13 and 14, respectively. The digital signals output from the A / A converters 13 and 14 are subjected to unnecessary wave suppression and waveform shaping by the digital filters 15 and 16 and input to the demodulator 27.

  The output signal 29 of the I signal / Q signal output from the digital filters 15 and 16 is input to the detector 20 that detects the SN ratio of the output signal 29, outputs the detection signal 25, and passes it to the control unit 17. .

  The low noise amplifier 3, the mixers 4, 5 and the local buffer 10 are bias-corrected by control signals 18, 19, 24 corresponding to the detection signal 25. This bias correction is performed so that the S / N ratio detected by the detector 20 is maximized. Since secondary distortion interference appears as degradation of the SN ratio in the demodulator, it is possible to suppress the secondary distortion interference by detecting this SN ratio and correcting the bias so that the SN ratio is maximized. is there.

  Next, the operation of optimizing the S / N ratio of the received signal in the receiving system circuit 56 of the first embodiment will be described using the flowchart of FIG.

  First, after reception, the S / N ratio is detected by the detector 20 (step S101), and the required S / N ratio required in the receiving system is compared with the control unit 17 (step S102). If the detected SN ratio is less than or equal to the required SN ratio, the bias of the low noise amplifier 3 is corrected and the SN ratio is detected again (steps S103 and S104).

  These steps S101 to S104 are repeated while correcting the bias, and communication is started when the detected SN ratio is equal to or higher than the required SN ratio (step S105). If the required signal-to-noise ratio cannot be obtained even after the bias sweep is completed (step 103), the bias correction of the mixers 4 and 5 is performed as the next operation (steps S106 to S109).

  If the SN ratio after the bias correction of the mixers 4 and 5 is equal to or greater than the required SN ratio (step S107), communication is started (step S105). If the required S / N ratio is not obtained after the mixer bias sweep, the bias correction of the local buffer unit 10 is performed next (steps S110 to S112). If the SN ratio after bias correction of the local buffer 10 is equal to or greater than the required SN ratio (step S111), communication is started (step S105).

  In the flowchart of FIG. 2, the case where three blocks of the low noise amplifier, the mixer, and the local buffer are corrected as the bias correction block is shown, but correction may be performed on any one or two blocks.

  Thus, according to the first embodiment, the S / N ratio of the I signal / Q signal is detected, and the bias conditions of the low noise amplifier 3, the mixers 4 and 5, and the local buffer 10 are changed according to the detection result. Thus, the SN ratio can be improved.

  Since the secondary distortion interference appears as degradation of the SN ratio in the demodulator, there is an effect that the secondary distortion interference can be suppressed by correcting the bias so that the SN ratio becomes maximum.

  In this embodiment, the bias correction is performed so that the SN ratio detected by the detector 20 is maximized. For example, as shown in FIG. Correction may be performed so that is minimized.

  In this case, the reception circuit 56 includes a low noise amplifier 3, mixers 4 and 5, a local buffer 10 including a 90-degree phase shifter, a VCO (oscillation circuit) 7, amplification circuits 8 and 9, and A / D (Analog / Digital). The converters 13 and 14, the analog filters 11 and 12, the digital filters 15 and 16, the demodulation unit 27, and the control unit 17 have the same configuration as that in FIG. 1, except that the detector 20 is eliminated and the detection is performed. A device 52 is newly provided.

  The detector 52 directly detects a second-order distortion component from the I / Q signals output from the analog filters 11 and 12, and passes this detection signal 25 to the control unit 17.

  The low noise amplifier 3, the mixers 4, 5, and the local buffer 10 are bias-corrected by control signals 24, 19, 18 corresponding to the detection signal 25, respectively. This bias correction is performed so that the second-order distortion component detected by the detector 25 is minimized, thereby enabling suppression of second-order distortion interference.

(Embodiment 2)
FIG. 4 is an explanatory diagram showing a circuit configuration example of a mixer provided in the receiving apparatus according to Embodiment 2 of the present invention.

  In the second embodiment, FIG. 4 is a circuit diagram showing an example of the circuit configuration of the mixers 4 and 5 provided in the reception system circuit 56 shown in FIG. 1 of the first embodiment.

  As shown in the figure, the I-side mixer 4 includes a Gilbert cell 41, a buffer 43, and a current source 46. The Q-side mixer 5 includes a Gilbert cell 42, a buffer 44, a current source 47, and a control circuit. 45.

  The received signal inputs 23 and 24 are input to the I-side and Q-side buffers 43 and 44, respectively, and the local signals 6 and 21 are input to the Gilbert cells 41 and 42, respectively. From the mixer, an output signal 28 for the I signal and an output signal 30 for the Q signal are output.

  In this case, the control signal 19 from the control unit 17 (FIG. 1) is input to the control circuit 45, and the bias conditions of the Gilbert cells 41 and 42 are corrected by the control signal 55 from the control circuit 45, respectively.

  Thereby, in the second embodiment, the bias of the Gilbert cell is corrected so that the S / N ratio of the I signal and the Q signal is maximized or the secondary distortion component of the I signal and the Q signal is minimized. Therefore, it is possible to improve the reception characteristics of the reception device.

(Embodiment 3)
FIG. 5 is an explanatory diagram showing a circuit configuration example of a mixer provided in the receiving apparatus according to Embodiment 3 of the present invention.

  In the third embodiment, FIG. 5 is a circuit diagram showing another example of the circuit configuration of the mixers 4 and 5 shown in the second embodiment (FIG. 4).

  In this case, as shown, the I-side mixer 4 includes a Gilbert cell 41, a buffer 43, and a current source 46, and the Q-side mixer 5 includes a Gilbert cell 42, a buffer 44, and a current source 47. It is constituted by.

  The received signal inputs 23 and 24 are input to the I side and Q side buffers, respectively, and the local signals 6 and 21 are input to the Gilbert cells 41 and 42, respectively. From the mixers 4 and 5, an I signal 28 and a Q signal 30 are output, respectively.

  In the mixers 4 and 5 in FIG. 5, the control signal 19 from the control unit 17 is input to the control circuit 45, and the bias conditions of the buffers 43 and 44 are corrected by the control signal 55 from the control circuit 45.

  Thereby, in the third embodiment, the bias of the Gilbert cell is corrected so that the S / N ratio of the I signal and the Q signal is maximized or the secondary distortion component of the I signal and the Q signal is minimized. This makes it possible to improve the reception characteristics of the receiving apparatus.

(Embodiment 4)
FIG. 6 is an explanatory diagram showing a circuit configuration example of a mixer provided in the receiving apparatus according to Embodiment 4 of the present invention.

  In the fourth embodiment, another circuit configuration example of the mixers 4 and 5 shown in the second and third embodiments (FIGS. 4 and 5) is shown.

  As shown in FIG. 6, the I-side mixer 4 includes a Gilbert cell 41, a buffer 43, and a current source 46, and the Q-side mixer 5 includes a Gilbert cell 42, a buffer 44, and a current source 47. It is configured.

  The received signal inputs 23 and 24 are input to the buffers 43 and 44, respectively, and the local signals 6 and 21 are input to the Gilbert cells 41 and 42, respectively. From the mixers 4 and 5, an I signal 28 and Q signals 28 and 30 are output, respectively.

  In the mixers 4 and 5 shown in FIG. 6, the control signal 19 from the control unit 17 is input to the control circuit 45, and the bias conditions of the constant current sources 46 and 477 are corrected by the control signal 55 from the control circuit 45.

  Thereby, also in the fourth embodiment, the bias of the Gilbert cell is corrected so that the SN ratio of the I signal and the Q signal is maximized, or the secondary distortion component of the I signal and the Q signal is minimized. And reception characteristics of the receiving apparatus can be improved.

(Embodiment 5)
FIG. 7 is an explanatory diagram showing a circuit configuration example of a mixer provided in the receiving apparatus according to the fifth embodiment of the present invention.

  The fifth embodiment shows another circuit configuration example of the mixers 4 and 5 shown in the second to fourth embodiments (FIGS. 4 to 6).

  In this case, as shown in FIG. 7, the mixers 4 and 5 include a compensation circuit having the same configuration as that of the above-described second to fourth embodiments including the Gilbert cells 41 and 42, the buffers 43 and 44, and the current sources 46 and 47. (Bias correction means) 48 to 51 are newly provided.

  The Gilbert cells 41 and 42 are respectively composed of four mixer transistors, and the compensation circuits 48 to 51 are connected to the output terminals 30A and 30B of the Gilbert cell 41 and the output terminals 28A and 28B of the Gilbert cell 42, respectively. The bias of the compensation circuits 48 to 51 is corrected by the control signal 19.

  This configuration also makes it possible to correct the Gilbert cell bias so that the signal-to-noise ratio of the I and Q signals is maximized, or the secondary distortion component of the I and Q signals is minimized.

  Thereby, also in the fifth embodiment, it is possible to improve the reception characteristics in the reception apparatus.

  In the fifth embodiment, the compensation circuits 48 to 51 are provided in the mixers 4 and 5. However, for example, as shown in FIG. 8, the output terminal 30A of the Gilbert cell 41 and the reference potential (ground) VSS. A resistor (bias correction means) 53 may be connected between the two.

  This also makes it possible to correct the Gilbert cell bias so that the signal-to-noise ratio of the I signal and Q signal is maximized, or to minimize the second-order distortion component of the I signal and Q signal. Can be improved.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  The present invention is suitable for a technique for improving reception characteristics in a receiving apparatus that receives a digitally modulated high-frequency signal such as a portable terminal.

It is a block diagram in the receiver by Embodiment 1 of this invention. 3 is a flowchart showing an example of an operation for optimizing an S / N ratio of a received signal in the receiving apparatus of FIG. It is a block diagram in the receiver by other embodiment of this invention. It is explanatory drawing which shows the circuit structural example of the mixer provided in the receiver by Embodiment 2 of this invention. It is explanatory drawing which shows the circuit structural example of the mixer provided in the receiver by Embodiment 3 of this invention. It is explanatory drawing which shows the circuit structural example of the mixer provided in the receiver by Embodiment 4 of this invention. It is explanatory drawing which shows the circuit structural example of the mixer provided in the receiver by Embodiment 5 of this invention. It is explanatory drawing which shows an example of the circuit of the mixer provided in the receiver by other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Antenna input terminal, 2 ... Splitter, 3 ... Low noise amplifier, 4, 5 ... Mixer, 7 ... VCO, 8, 9 ... Amplifier circuit, 10 ... 90 degree phase shifter / local buffer, 11, 12 ... Analog Filters 13, 14, A / D converters, 15, 16 ... Digital filters, 17 ... Control unit, 20 ... Detector, 27 ... Demodulator, 30A, 30B, 28A, 28B ... Output terminal, 41, 42 ... Gilbert Cell, 43, 44 ... Buffer, 45 ... Control circuit, 46, 47 ... Current source, 48-51 ... Compensation circuit (bias correction means), 52 ... Detector, 53 ... Resistance (bias correction means), 56 ... Reception system circuit.

Claims (8)

A reception device including an analog signal processing unit that receives a high-frequency signal and converts the frequency, and a signal demodulation unit that demodulates the reception signal,
A receiving apparatus comprising bias correcting means for correcting a bias of the analog signal processing section so that an S / N ratio of a demodulated signal is maximized. A reception device including an analog signal processing unit that receives a high-frequency signal and converts the frequency, and a signal demodulation unit that demodulates the reception signal,
A receiving apparatus comprising bias correcting means for correcting a bias of the analog signal processing unit so that a distortion component generated in the analog signal processing unit is minimized. The receiving apparatus according to claim 1 or 2,
The receiving apparatus according to claim 1, wherein the bias correcting unit corrects at least one bias of a mixer, a low noise amplifier, and a local buffer. The receiving device according to claim 3,
2. A receiver according to claim 1, wherein the bias correcting means for correcting the bias of the mixer comprises a resistor connected between a collector of a mixer transistor constituting the mixer and a reference potential. The receiving device according to claim 3,
Bias correction means for correcting the bias of the mixer,
A receiving apparatus comprising: a compensation circuit connected to an output terminal of a Gilbert cell constituting the mixer, wherein the bias of the mixer is corrected by correcting the bias of the compensation circuit. A method for optimizing reception characteristics when receiving a high-frequency signal and converting the frequency,
A method for optimizing a reception characteristic, comprising: detecting a demodulated signal in a signal demodulating unit that demodulates a received signal; and controlling a bias of an analog signal processing unit so that an S / N ratio of the demodulated signal is maximized. A method for optimizing reception characteristics when receiving a high-frequency signal and converting the frequency,
A reception characteristic characterized by detecting a second-order distortion component of a detection signal generated in the analog signal processing unit and controlling a bias of the analog signal processing unit so that the second-order distortion component of the detection signal is minimized. Optimization method. The method for optimizing reception characteristics according to claim 6 or 7,
The method for optimizing the bias includes correcting the bias of at least one of a mixer, a low-noise amplifier, and a local buffer.

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