JP5332468B2 - Receiver circuit - Google Patents

Description

  The present invention relates to a communication device such as a wireless portable terminal, and more particularly to a receiving circuit having an impedance matching switching function.

  In a receiving circuit of a communication device such as a wireless portable terminal, an RF (Radio Frequency) signal received by an antenna is amplified and an RF signal is output to a subsequent mixing circuit or the like. There is a possibility of saturation. On the other hand, when the received electric field strength is small, there is a possibility that a sufficient level of RF signal cannot be obtained. Therefore, in the receiving circuit, an amplifier having a variable gain is used, and the gain of the amplifier is controlled according to the magnitude of the received electric field intensity.

  FIG. 8 shows the configuration of the amplifier portion of the receiving circuit disclosed in Patent Document 1 and Patent Document 2. In FIG. 8, 1000 is an input side matching unit, 1001 is an amplifier with variable gain, 1002 is an output side matching unit, and 1003 is a control unit. A received signal received by an antenna (not shown) is input to the input matching unit 1000. The input side matching unit 1000 sets the input side impedance matching to an optimum value. Here, the input side impedance matching is controlled by the input side matching control signal output from the control unit 1003 in accordance with the power of the output signal output from the amplifier 1001.

  The received signal subjected to the input side matching is amplified by the amplifier 1001 with a gain corresponding to the gain control signal output from the control unit 1003, and is output to the output side matching unit 1002. The output side matching unit 1002 sets the output side impedance matching to an optimum value. Here, the output-side impedance matching is controlled by the output-side matching control signal output from the control unit 1003 in accordance with the power of the output signal output from the amplifier 1001, similarly to the input-side impedance matching.

  The input side matching unit 1000 and the output side matching unit 1002 are each composed of a varicap capacitor and a variable coil. The control unit 1003 outputs an input side matching control signal to the input side matching unit 1000. In accordance with this control signal, the capacitance value of the varicap capacitor of the input side matching unit 1000 and the inductance value of the variable coil change, and the input side impedance matching is controlled to be optimum. Similarly, the control unit 1003 outputs an output side matching control signal to the output side matching unit 1002. In accordance with this control signal, the capacitance value of the varicap capacitor of the output side matching unit 1002 and the inductance value of the variable coil are changed so that the output side impedance matching is optimized.

  The input impedance of the amplifier 1001 changes as the gain changes according to the gain control signal. When the input impedance of the amplifier 1001 changes, the frequency characteristics of a band-pass filter (not shown) connected to the input terminal of the input side matching unit 1000 fluctuate due to the influence of the input impedance change. Since the input impedance matching is adjusted according to the power of the output signal of the amplifier 1001, the input impedance on the amplifier side viewed from the input terminal of the input side matching unit 1000 can be made constant. Variations in the frequency characteristics of the pass filter can be suppressed.

JP 2002-217660 A JP 2000-323944 A

  However, in the receiving circuits disclosed in Patent Document 1 and Patent Document 2, the gain of the amplifier continuously changes. Therefore, the characteristics of the receiving circuit must be adjusted in each of a plurality of gain states. There was a problem that the number of points increased. That is, in the receiving circuits disclosed in Patent Document 1 and Patent Document 2, it is necessary to perform adjustment in each gain state while changing the gain of the amplifier.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a receiving circuit that can reduce the number of adjustment points and facilitate adjustment in the manufacturing process.

The receiving circuit of the present invention is capable of switching matching constants, a matching circuit to which a received signal received by an antenna is input, a band-pass filter provided on the input side of the matching circuit, and a two-stage gain. A first amplifying means for amplifying the output signal of the matching circuit, a converting means for converting the output signal of the first amplifying means into a signal of a baseband frequency, and continuous gain switching. A second amplifying means for amplifying the output signal of the converting means, and a set gain value for designating a gain so that the output signal of the second amplifying means has a predetermined desired level. And a gain switching signal for operating at a first gain when the received electric field strength is less than or equal to a predetermined threshold value is output to the first amplifying device, and the received electric field strength exceeds the threshold value. A gain control means for outputting to the first amplifying means a gain switching signal for operating with a second gain smaller than the first gain, and the first amplifying means for operating with the second gain. The input impedance of the first amplifying means including the matching circuit when the first amplifying means is operating at the first gain when the first amplifying means is operating at the first gain. Matching circuit control means for switching the matching constant of the matching circuit so as to match the input impedance of the first amplifying means, and first correction data for correcting gain fluctuations due to frequency characteristics of the bandpass filter are stored. A correction table; and gain correction means for correcting the set gain value so that the frequency characteristic of the receiving circuit becomes a desired characteristic based on the first correction data; The matching circuit control means outputs either the control voltage corresponding to the first gain or the control voltage corresponding to the second gain to the matching circuit in response to the gain switching signal, and from the outside The control voltage is corrected based on the ambient temperature indicated by the input temperature measurement value so that the matching constant of the matching circuit becomes a desired value .

  According to the present invention, the matching circuit control means changes the matching constant of the matching circuit in accordance with the gain switching signal, so that the input of the first amplifying means including the matching circuit when viewed from the input port of the matching circuit. Since the impedance can be made constant regardless of the gain state of the first amplifying means, the matching between the band-pass filter existing on the input side of the matching circuit and the first amplifying means is always in an optimum state. It is possible to prevent the frequency characteristics of the receiving circuit from fluctuating. In the present invention, the gain of the first amplifying means can be switched in two stages, and the gain can be continuously switched in the second amplifying means, thereby enabling continuous gain switching in the entire receiving circuit. I have to. In the present invention, the input impedance fluctuation (frequency characteristic fluctuation of the receiving circuit) of the first amplifying means due to the gain switching of the first amplifying means is suppressed by switching the matching constant of the matching circuit, and further, Since the gain switching is performed in two stages, adjustment only needs to be performed when the first amplifying means is in the first gain state in the manufacturing process, and the adjustment process of the receiving circuit can be shortened.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of a receiving circuit according to the first embodiment of the present invention.
Referring to FIG. 1, a receiving circuit 100 according to the present embodiment includes a BPF (BPF: Band Pass Filter) 101, an LNA (Low Noise Amplifier) 104, and an impedance matching circuit for the LNA 104. 102, a matching circuit control unit 103, a mixer 105, a frequency synthesizer 106, a programmable gain amplifier (PGA) 110, a gain control unit 107, and an antenna 113. The mixer 105 and the frequency synthesizer 106 constitute conversion means for converting an RF signal into a baseband frequency signal.

The components shown in FIG. 1 generally operate as follows. The BPF 101 removes interference waves outside the reception band from the RF signal received by the antenna 113.
The LNA 104 amplifies the RF signal input from the BPF 101 via the matching circuit 102. The LNA 104 is configured to be able to switch between at least two stages of gains: a high gain and a low gain.

The matching circuit 102 is a circuit composed of a plurality of lumped constant elements, and includes a variable element whose capacitance or inductance value varies depending on the applied voltage as the lumped constant element.
The matching circuit control unit 103 outputs a control voltage of either H / L according to the LNA gain switching signal output from the gain control unit 107 in order to change the constant of the variable element 1021. Which level of H / L is to be output may be arbitrarily set.

The frequency synthesizer 106 generates and outputs a local signal. The mixer 105 multiplies the RF signal output from the LNA 104 with the local signal output from the frequency synthesizer 106 to convert the signal to a baseband frequency signal.
The PGA 110 amplifies the output signal of the mixer 105 to a desired amplitude level and outputs it as an IQ signal.

  The gain control unit 107 determines the gain of the PGA 110 so that the level of the IQ signal becomes a predetermined level that is defined in advance, and outputs a set gain value that specifies this gain to the PGA 110. The gain control unit 107 has a function of calculating the received electric field strength at the antenna 113 and outputs an LNA gain switching signal to the matching circuit control unit 103 and the LNA 104 according to the calculated received electric field strength. The gain control unit 107 controls the LNA 104 to operate at a low gain when the received electric field strength exceeds a predetermined threshold, and causes the LNA 104 to operate at a high gain when the received electric field strength is less than the threshold. Control.

  Next, the operation of the first exemplary embodiment of the present invention will be described in detail with reference to FIG. First, when the received electric field strength is equal to or smaller than a certain threshold, the gain control unit 107 sets the LNA 104 to a high gain state by an LNA gain switching signal. In response to the LNA gain switching signal, the matching circuit control unit 103 outputs an L level control voltage Vl. As a result, the matching circuit 102 is in a state in which matching is achieved with respect to the high gain state of the LNA 104. At this time, the impedance viewed from the output port of the BPF 101 is referred to as a first impedance.

  Next, when the received electric field strength is greater than or equal to a certain threshold, the gain control unit 107 sets the LNA 104 to a low gain state by an LNA gain switching signal. In response to the LNA gain switching signal, the matching circuit control unit 103 outputs an H level control voltage Vh. As a result, the matching circuit 102 is in a state in which matching is achieved with respect to the low gain state of the LNA 104. At this time, the impedance viewed from the output port of the BPF 101 is referred to as a second impedance.

  Since the second impedance is adjusted by the matching circuit 102 to match the first impedance, the frequency characteristics of the BPF 101 are stable regardless of the switching of the gain of the LNA 104.

  The frequency characteristic of the LNA 104 is normally designed so as to have a sufficiently wide band as compared with the frequency characteristic of the BPF 101 in both high and low gain states. For this reason, the frequency characteristic of the BPF 101 is dominant in the frequency characteristic of the receiving circuit 100. Therefore, a sufficient frequency correction effect can be obtained regardless of the gain state of the LNA 104 only by adjusting the receiving circuit 100 when the LNA 104 is in the high gain state.

  As described above, in this embodiment, the matching circuit control unit 103 changes the matching constant of the matching circuit 102 according to the gain switching signal, so that the matching circuit 102 when viewed from the input port of the matching circuit 102 is used. Can be made constant regardless of the gain state of the LNA 104. In this embodiment, the gain switching of the LNA 104 is performed in two stages, and the PGA 110 allows continuous gain switching, thereby enabling continuous gain switching for the entire receiving circuit.

  In this embodiment, since the input impedance fluctuation (frequency characteristic fluctuation of the receiving circuit) of the LNA 104 due to the gain switching of the LNA 104 is suppressed by switching the matching constant of the matching circuit 102, and further, the switching of the gain of the LNA 104 is performed in two stages. In the process, adjustment only needs to be performed when the LNA 104 is in the high gain state, and the adjustment process of the receiving circuit can be shortened.

[Second Embodiment]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 2 is a block diagram showing a configuration example of a receiving circuit according to the second embodiment of the present invention. The same components as those in FIG. In the present embodiment, the first embodiment will be described more specifically.

  Referring to FIG. 2, the receiving circuit 100a of the present embodiment includes a BPF 101, an LNA 104, a matching circuit 102, a matching circuit control unit 103, a mixer 105, a frequency synthesizer 106, a low pass filter (LPF: Low pass). filter) 109, PGA 110, gain control unit 107, gain correction unit 111, register 112, correction table 114, addition unit 108, and antenna 113.

The components shown in FIG. 2 generally operate as follows. Similar to the first embodiment, the LNA 104 is configured to be able to switch between at least two stages of gains: a high gain and a low gain.
FIG. 3 is a block diagram showing an outline of the configuration of the LNA 104. The LNA 104 includes an amplifier 1040 that amplifies the RF signal, a current control unit 1041 that controls supply of an operating current to the amplifier 1040 according to the LNA gain switching signal, and a signal path switching unit that switches the signal path according to the LNA gain switching signal. The switch 1042 is provided. The current control of the amplifier 1040 can be realized, for example, by controlling a current source transistor that supplies a current to the amplifier 1040. The switch 1042 can be realized by a transistor, for example.

  When the LNA gain switching signal input from the gain control unit 107 specifies the low gain state, the current control unit 1041 turns off the current flowing through the amplifier 1040 and stops the operation of the amplifier 1040. The switch 1042 selects the output of the amplifier 1040 when the LNA gain switching signal designates the high gain state, but the output of the matching circuit 102 when the LNA gain switching signal designates the low gain state. Select.

  Thus, in the low gain state, a signal input from the BPF 101 via the matching circuit 102 is output to the mixer 105 by bypassing the amplifier 1040. Thus, since the signal path is switched, the input impedance of the LNA 104 varies depending on the gain state. In this embodiment, when the LNA 104 is in the low gain state, the current flowing through the amplifier 1040 is turned off, so that current consumption can be reduced.

  The matching circuit 102 is a circuit composed of a plurality of lumped constant elements, and includes a variable element whose capacitance or inductance value changes depending on the applied voltage as the lumped constant element. As the variable element, for example, use of a MEMS (Micro Electro-Mechanical System) device can be considered.

  FIG. 4 shows a configuration example of the matching circuit 102. Here, a configuration in which one inductor is used as each of the fixed elements 1022 and 1023 and one capacitance variable element is used as the variable element 1021 is shown. A variable capacitance diode can be used as the variable capacitance element. The circuit configuration shown in FIG. 4 is an example for explaining the operation, and the matching circuit 102 can be freely configured according to the input impedance of the LNA 104 actually applied.

  FIG. 5 shows a characteristic example of the variable constant 1021 in the present embodiment. The variable constant 1021 has a capacitance value of B [pF] when the LNA 104 has a high gain, and has a capacitance value of A [pF] when the LNA 104 has a low gain. That is, the variable constant 1021 becomes the capacitance value B [pF] when the L-level control voltage Vl is input from the matching circuit control unit 103, and the capacitance value A [pF when the H-level control voltage Vh is input. ]. The capacitance value B [pF] is selected so that the receiving sensitivity of the receiving circuit 100a is optimized.

  On the other hand, the capacitance value A [pF] is adjusted so that the impedance viewed from the output port of the BPF 101 is close to the input impedance of the LNA 104 during the high gain operation. Thereby, the variable constant 1021 minimizes the fluctuation of the input impedance due to the gain state of the LNA 104.

  The matching circuit control unit 103 outputs a control voltage of either H / L according to the LNA gain switching signal output from the gain control unit 107 in order to change the constant of the variable element 1021. Which level of H / L is to be output may be arbitrarily set. In the present embodiment, the matching circuit control unit 103 outputs an L level control voltage Vl when the LNA 104 operates at a high gain, and outputs an H level control voltage Vh when the LNA 104 operates at a low gain. To do. In the case where a plurality of variable elements are used in the matching circuit 102, a configuration in which a plurality of control voltages can be output may be employed.

  The frequency synthesizer 106 generates and outputs a local signal according to a frequency setting value input from the outside. The mixer 105 multiplies the RF signal output from the LNA 104 with the local signal output from the frequency synthesizer 106 to convert the signal to a baseband frequency signal.

  The LPF 109 removes interference waves outside the baseband from the output signal of the mixer 105. The PGA 110 amplifies the output signal of the LPF 109 to a desired amplitude level and outputs it as an IQ signal.

  The gain control unit 107 determines the gain of the PGA 110 so that the level of the IQ signal becomes a predetermined level specified in advance, and outputs a set gain value designating this gain to the PGA 110 via the addition unit 108. This set gain value is output as having a common value at a plurality of signal frequency points.

  The gain control unit 107 has a function of calculating the received electric field strength at the antenna 113 and outputs an LNA gain switching signal to the matching circuit control unit 103 and the LNA 104 according to the calculated received electric field strength. The gain control unit 107 controls the LNA 104 to operate at a low gain when the received electric field strength exceeds a predetermined threshold, and causes the LNA 104 to operate at a high gain when the received electric field strength is less than the threshold. Control. The received electric field strength can be calculated from, for example, the IQ signal level and the gain of the entire receiving circuit 100a.

  The register 112 stores a gain calibration value of the receiving circuit 100a from the antenna 113 to the input of the PGA 110 in order to absorb individual variations of the receiving circuit 100a. The gain control unit 107 can calculate the received electric field strength using the gain calibration value stored in the register 112, the gain set in the PGA 110, and the IQ signal level. The gain calibration value is obtained individually in the manufacturing process of the receiving circuit 100 a and is stored in the register 112. This calibration value must be prepared for each case where the gain of the LNA 104 is High gain / Low gain at a certain reference ambient temperature and reference reception frequency.

  If the LNA 104 is in the high gain state, the gain control unit 107 calculates the received electric field strength using the gain calibration value at the time of the high gain, the gain set in the PGA 110, and the IQ signal level, and the LNA 104 is in the low gain state. If there is, the received electric field strength is calculated using the gain calibration value at the low gain, the gain set in the PGA 110, and the IQ signal level.

  The correction table 114 stores correction data for correcting gain fluctuations of each device due to changes in ambient temperature, and correction data for correcting gain fluctuations due to the frequency characteristics of the BPF 101.

  The gain correction unit 111 obtains the current ambient temperature indicated by the temperature measurement value input from the outside, the reception frequency information (RF frequency information) indicated by the frequency setting value input from the outside, and the correction data of the correction table 114. The gain correction value for the reference ambient temperature and the set gain value of the reference reception frequency is calculated for each of a plurality of reception frequency points. The adding unit 108 adds the set gain value output from the gain control unit 107 and the gain correction value output from the gain correction unit 111 for each frequency point, and outputs the corrected set gain value to the PGA 110.

  The correction data for correcting the gain variation of each device due to changes in the ambient temperature is a value obtained in advance through experiments, etc., and indicates the relative gain difference of the device gain relative to the desired gain value at the reference ambient temperature. ing. This correction data is stored in the correction table 114 for each ambient temperature.

  The correction data for correcting the gain fluctuation due to the frequency characteristic of the BPF 101 is a value obtained by individually adjusting in the manufacturing process of the reception circuit 100a, and a desirable gain at the reference reception frequency in a state where the LNA 104 is set to the high gain. The relative gain difference amount of the gain of the BPF 101 with respect to the value is shown for each frequency point. This correction data is stored in the correction table 114 for each reception frequency point.

The gain correction unit 111 uses these correction data to calculate a gain correction value for the set gain value of the reference ambient temperature and the reference reception frequency for each of a plurality of reception frequency points.
By adding the set gain value and the gain correction value for each frequency point by the adding unit 108, the set gain value is corrected to a desired value at the reception frequency during operation.

Next, the operation of the second exemplary embodiment of the present invention will be described in detail with reference to FIG. 2, FIG. 3, FIG. 4, and FIG.
Similar to the first embodiment, when the received electric field strength is equal to or smaller than a certain threshold, the gain control unit 107 sets the LNA 104 to a high gain state by an LNA gain switching signal. In response to the LNA gain switching signal, the matching circuit control unit 103 outputs an L level control voltage Vl. As a result, the matching circuit 102 is in a state in which matching is achieved with respect to the high gain state of the LNA 104. At this time, the impedance viewed from the output port of the BPF 101 is referred to as a first impedance.

  Since the frequency characteristic of the loss of the BPF 101 is corrected by the gain correction unit 111, if the received signal level at the antenna 113 is the same, the gain control unit 107 outputs a constant set gain value regardless of the reception frequency.

  Next, when the received electric field strength is greater than or equal to a certain threshold, the gain control unit 107 sets the LNA 104 to a low gain state by an LNA gain switching signal. In response to the LNA gain switching signal, the matching circuit control unit 103 outputs an H level control voltage Vh. As a result, the matching circuit 102 is in a state in which matching is achieved with respect to the low gain state of the LNA 104. At this time, the impedance viewed from the output port of the BPF 101 is referred to as a second impedance.

Since the second impedance is adjusted by the matching circuit 102 so as to match the first impedance, the frequency characteristic of the BPF 101 becomes stable regardless of the switching of the gain of the LNA 104.
As described in the first embodiment, the frequency characteristic of the BPF 101 is dominant in the frequency characteristic of the receiving circuit 100a. Therefore, even if the gain correction unit 111 calculates the gain correction value for correcting the gain fluctuation by the frequency characteristic of the BPF 101 using the data of the correction table 114 adjusted when the LNA 104 is in the high gain state, the LNA 104 A sufficient frequency correction effect can be obtained regardless of the gain state. Thus, in this embodiment, the effects described in the first embodiment can be obtained.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. FIG. 6 is a block diagram showing a configuration example of a receiving circuit according to the third embodiment of the present invention. The same components as those in FIG. 2 are denoted by the same reference numerals.
As compared with the second embodiment, the receiving circuit 300 of this embodiment has a temperature correction table 315 added to the matching circuit control unit 103a, and a D / A between the matching circuit control unit 103a and the matching circuit 102a. A difference is that a converter 316 is added and a temperature measurement value is input to the matching circuit control unit 103a. The functions of the other configurations are the same as those in the second embodiment, and a description thereof will be omitted.

  FIG. 7 shows a configuration example of the matching circuit 102a. The matching circuit 102a includes a tunable variable element 3021 whose constant (capacitance in this case) changes according to the voltage output from the D / A converter 316, and one of the H / L controls output from the matching circuit control unit 103a. It is composed of a variable element 3022 whose inductance value changes according to the voltage, and a fixed element 3023. A variable inductor is used as the variable element 3022, and an inductor is used as the fixed element 3023. The circuit configuration shown in FIG. 7 is an example for explaining the operation, and the matching circuit 102a can be freely configured as appropriate according to the LNA 104 actually applied.

  The matching circuit control unit 103a outputs a control voltage of either H / L according to the LNA gain switching signal output from the gain control unit 107, as in the second embodiment. Thereby, the constant (inductance value here) of the variable element 3022 can be changed. Also, the matching circuit control unit 103a sends either the digital value of the control voltage corresponding to the high gain state or the digital value of the control voltage corresponding to the low gain state to the D / A converter 316 in response to the LNA gain switching signal. Output. In accordance with the digital value, the D / A converter 316 applies a voltage to the tunable variable element 3021. As a result, the constant (capacitance here) of the tunable variable element 3021 can be changed.

  In the present embodiment, in addition to the binary control voltage, any voltage can be output from the matching circuit control unit 103a via the D / A converter 316. Thus, the present embodiment has an effect of facilitating the design for making the second impedance coincide with the first impedance.

  Further, the temperature correction table 315 stores temperature characteristic data of the tunable variable element 3021. The matching circuit control unit 103a sets the matching constant of the matching circuit 102a to a desired value based on the current ambient temperature indicated by the temperature measurement value input from the outside and the temperature characteristic data stored in the temperature correction table 315. The output voltage to the D / A converter 316 is corrected. As a result, in the present embodiment, it is possible to correct a change in the constant of the tunable variable element 3021 due to the ambient temperature, and it is possible to stably maintain the input impedance of the LNA 304 even when the ambient temperature changes. Have.

  The present invention can be applied to a communication apparatus such as a wireless portable terminal in which an amplifier that amplifies a received signal has a gain switching function.

1 is a block diagram illustrating a configuration example of a receiving circuit according to a first embodiment of the present invention. It is a block diagram which shows the structural example of the receiver circuit which concerns on the 2nd Embodiment of this invention. It is a block diagram which shows the outline of a structure of LNA based on the 2nd Embodiment of this invention. It is a circuit diagram which shows the structural example of the matching circuit which concerns on the 2nd Embodiment of this invention. It is a figure which shows the example of a characteristic of the variable constant of the matching circuit which concerns on the 2nd Embodiment of this invention. It is a block diagram which shows the structural example of the receiver circuit which concerns on the 3rd Embodiment of this invention. It is a circuit diagram which shows the structural example of the matching circuit which concerns on the 3rd Embodiment of this invention. It is a block diagram which shows the structural example of the amplifier part of a related receiving circuit.

Explanation of symbols

  100, 100a, 300 ... receiving circuit, 101 ... band pass filter, 102, 102a ... matching circuit, 103, 103a ... matching circuit control unit, 104 ... LNA, 105 ... mixer, 106 ... frequency synthesizer, 107 ... gain control unit, DESCRIPTION OF SYMBOLS 108 ... Addition part, 109 ... Low pass filter, 110 ... Programmable gain amplifier, 111 ... Gain correction part, 112 ... Register, 113 ... Antenna, 114 ... Correction table, 315 ... Temperature correction table, 316 ... D / A converter, 1021, 3022 ... Variable element, 1022, 1023, 3023 ... Fixed element, 3021 ... Tunable variable element.

Claims (9)

Matching constants can be switched, and a matching circuit to which the received signal received by the antenna is input;
A bandpass filter provided on the input side of the matching circuit;
A first amplifying means capable of switching gains in two stages and amplifying an output signal of the matching circuit;
Conversion means for converting the output signal of the first amplification means into a signal of a baseband frequency;
A second amplifying means capable of continuously switching gains and amplifying the output signal of the converting means;
When a set gain value specifying a gain is output to the second amplifying means so that the output signal of the second amplifying means becomes a predetermined desired level, and the received electric field strength is below a predetermined threshold value Outputs a gain switching signal for operating at a first gain to the first amplifying means, and a gain switching signal for operating at a second gain smaller than the first gain when the received electric field strength exceeds the threshold. Gain control means for outputting to the first amplification means,
When the first amplifying means operates at the second gain, the input impedance of the first amplifying means including the matching circuit is such that the first amplifying means has the first gain. Matching circuit control means for switching the matching constant of the matching circuit so as to match the input impedance of the first amplifying means including the matching circuit when operating ;
A correction table storing first correction data for correcting gain fluctuations due to frequency characteristics of the bandpass filter;
Gain correction means for correcting the set gain value so that the frequency characteristic of the receiving circuit becomes a desired characteristic based on the first correction data;
The matching circuit control means outputs either a control voltage corresponding to the first gain or a control voltage corresponding to the second gain to the matching circuit in response to the gain switching signal, and from the outside A receiving circuit , wherein the control voltage is corrected based on an ambient temperature indicated by an input temperature measurement value so that a matching constant of the matching circuit becomes a desired value . The receiving circuit according to claim 1,
The first amplification means includes
An amplifier to which an output signal of the matching circuit is input;
Current control means for turning off the current flowing through the amplifier when the gain switching signal specifies the second gain;
And a signal path switching means for outputting a signal input from the matching circuit through a signal path not passing through the amplifier when the gain switching signal specifies the second gain. Receiving circuit. The receiving circuit according to claim 1 or 2,
The matching circuit includes a variable capacitance element as means capable of switching the matching constant. The receiving circuit according to claim 3, wherein
The receiving circuit, wherein the variable capacitance element is a variable capacitance diode. The receiving circuit according to claim 3, wherein
In accordance with the gain switching signal, the matching circuit control unit changes the capacitance of the capacitance variable element by using either a control voltage corresponding to the first gain or a control voltage corresponding to the second gain. A receiving circuit. The receiving circuit according to claim 3, wherein
Furthermore, a D / A converter is provided between the matching circuit control means and the matching circuit, which converts a digital value output from the matching circuit control means into a control voltage and outputs the control voltage to the matching circuit. Receiving circuit. The receiving circuit according to claim 1 or 2,
The matching circuit includes a variable inductance element as means for switching the matching constant. The receiving circuit according to claim 7 ,
The matching circuit control means changes the inductance of the variable inductance element according to either the control voltage corresponding to the first gain or the control voltage corresponding to the second gain in response to the gain switching signal. A receiving circuit. The receiving circuit according to claim 1 ,
The correction table stores second correction data for correcting a gain variation of the receiving circuit due to a change in ambient temperature,
The gain correction means corrects the set gain value based on an ambient temperature indicated by a temperature measurement value input from the outside and the second correction data.

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