JP2011147167A - Signal processing circuit and signal processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a signal processing circuit which, when inputting a signal to a mixer to convert the signal into a desired frequency, can reduce a distortion of the input signal due to temperature. <P>SOLUTION: When a detection result of a temperature sensor 133 is lower than a prescribed temperature, an attenuation factor of a first variable attenuator 102 is large, and that of a second variable attenuator 108 is small. When the detection result is within a range of the prescribed temperature or higher, the relation of attenuation factors is inverted. In a mixer 104 which has the gain increased to increase the distortion at a low temperature, the increase in distortion of IM (Inter Modulation) 3 can be prevented by increasing the attenuation factor at a low temperature. When a mixer that has, in a preceding stage thereof, an amplifier of which the amplification factor rises at a low temperature is used, the increase in the distortion can be prevented in the same manner. The amplification factor may be adjusted instead of the attenuation factor. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a signal processing circuit using a mixer that creates an intermediate frequency, and is particularly suitable for a transmission circuit or a reception circuit constituting a communication device such as an access wireless device, so as to remove distortion of a signal to be processed. The present invention relates to a signal processing circuit.

  A transmitter circuit that performs transmission after inputting a local signal output from a local oscillator to a mixer and up-converting a transmission signal to a desired frequency is generally used for a transmitter. Although the mixer is used to create an intermediate frequency, since it is a non-linear circuit, IM (Inter Modulation) 3 that is a third-order distortion is generated with respect to the input signal. Therefore, the transmission circuit is generally provided with a variable amplifier in front of the mixer, and is devised so that its input does not become oversaturated (see, for example, Patent Document 1). In other words, by controlling the amplification factor of the variable amplifier, distortion due to an excessive input of the mixer is prevented.

  The mixer generates distortion even at a low temperature in addition to such an excessive input. Therefore, when trying to use the transmission circuit in a wide temperature range, distortion at a low temperature by the mixer becomes a problem. When the temperature is low, the characteristics of the mixer deteriorate, and the circuit output deteriorates due to IM3.

  FIG. 9 shows the main part of an example of a conventional transmission circuit. The transmission circuit 500 includes a mixer 502 for inputting a transmission signal 501 to be transmitted and up-converting the frequency. A local signal 504 as an oscillation frequency of the local oscillator 503 is input to the mixer 502. The transmission signal 505 after being up-converted by the mixer 502 passes through the variable attenuator 506 and is attenuated. The attenuated transmission signal 507 is amplified by the amplifier 508 and then sent to the directional coupler 509. It is designed to be entered.

  The directional coupler 509 inputs the transmission signal 511 branched thereby, to the detector 512. The detection output 513 of the detector 512 is input to the low-pass filter 514, and this output 515 is input to the operational amplifier 517 through the first resistor 516. Here, the output 518 of the operational amplifier 517 becomes the control input of the variable attenuator 506.

  The operational amplifier 517 has a positive (+) input terminal grounded, and a negative (−) input terminal connected to one end of the first resistor 516 has a second resistor 519 for feedback that determines a gain between the output terminal and the negative (−) input terminal. Is connected.

  In such a conventional transmission circuit 500, in order to keep the original transmission output 521 from the directional coupler 509 constant regardless of the temperature, the transmission signal 511 is branched and the signal level is detected by the detector 512. Then, it is fed back to the variable attenuator 506 as the output 518 of the operational amplifier 517. That is, when the transmission output 521 of the transmission circuit 500 decreases, the attenuation amount of the variable attenuator 506 is decreased by the change of the output 518. On the contrary, when the transmission output 521 of the transmission circuit 500 increases, the attenuation amount of the variable attenuator 506 is increased by the change of the output 518.

JP 2000-244353 (paragraphs 0020 to 0023, FIG. 1)

  However, in the conventional transmission circuit 500 as shown in FIG. 9, when the environmental temperature decreases, the distortion of the mixer 502 increases with this, and the quality of the transmission output 521 deteriorates. Therefore, it is considered that the signal level of the transmission signal 501 input to the mixer 502 is uniformly reduced regardless of the temperature. However, since the signal level of the local signal 504 output from the local oscillator 503 is constant, there is a problem that the ratio of the amount of local leak due to this increases relatively, and the transmission signal 521 is deteriorated. Further, when the gain of the amplifier 508 decreases at a high temperature, there is a problem that the gain of the transmission signal 521 becomes insufficient when the signal level of the transmission signal 501 remains lowered.

  As described above, the problem of distortion due to temperature is taken up for the transmission circuit, but the same problem occurs in the reception circuit using the mixer.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a signal processing circuit capable of reducing distortion due to temperature when a signal is input to a mixer and converted to a desired frequency.

  The signal processing circuit of the present invention includes (a) an oscillator, (b) a mixer that converts the frequency of the input signal by mixing the oscillation output of the oscillator and the input signal, and (c) detecting the temperature of the mixer. And (d) a signal level of the input signal in a predetermined temperature range that is arranged in front of the mixer and in which the distortion of the mixer increases according to the detection result of the temperature detection unit. (E) the signal level adjusting means controls each attenuation amount in a quadratic function according to the temperature change detected by the temperature detecting means.

  As described above, according to the present invention, the signal level input to the mixer is relatively decreased only in a predetermined temperature range where the distortion of the mixer is large, so that the signal level is insufficient in other temperature ranges. Things don't happen. Further, since a circuit for detecting temperature and a circuit for adjusting a signal level input to the mixer may be provided, signal distortion can be removed over a wide temperature range with a simple circuit.

It is a block diagram which shows the principal part of the transmission circuit in embodiment of this invention. It is a characteristic view showing the relationship between IM3 and temperature. It is explanatory drawing showing the mode of switching of the attenuation amount of a 1st variable attenuator and a 2nd variable attenuator in this Embodiment. It is the characteristic view which showed the level diagram in the normal temperature of the transmission circuit of this Embodiment. It is the characteristic view which showed the level diagram in the low temperature of the transmission circuit of this Embodiment. It is a block diagram showing the transmission circuit in the 1st modification of this invention. It is a block diagram showing the transmission circuit in the 2nd modification of this invention. It is explanatory drawing of the ROM table for controlling the amount of attenuation in the 2nd modification. It is a block diagram showing the principal part about an example of the conventional transmission circuit.

  <Embodiment of the Invention>

  Next, an embodiment of the present invention will be described.

  FIG. 1 shows a configuration of a main part of a transmission circuit according to an embodiment of the present invention. The transmission circuit 100 includes a first variable attenuator (ATT) 102 that inputs a transmission signal 101 to be transmitted. The transmission signal 103 attenuated according to the temperature by the first variable attenuator 102 is input to the mixer 104, mixed with the local signal 106 as the oscillation frequency of the local oscillator 105, and up-converted to a desired frequency. It has become. The transmission signal 107 after being up-converted by the mixer 104 passes through the second variable attenuator 108 and is attenuated according to the temperature. The attenuated transmission signal 109 is amplified by the amplifier 110 and then directionally coupled. Is input to the device 111. Note that the mixer 104 of this embodiment has a characteristic that the gain increases and distortion increases at low temperatures.

  The directional coupler 111 inputs the transmission signal 113 branched by this to the detector 114. The detection output 115 of the detector 114 is input to the low-pass filter 116, and this output 117 is sent to the first operational amplifier 119 via the first resistor 118 and to the second operational amplifier 122 via the second resistor 121. Each is input to. Here, the output 123 of the first operational amplifier 119 becomes a control input of the first variable attenuator 102.

  The first operational amplifier 119 has a positive input terminal grounded, and a negative input terminal connected to one end of the first resistor 118 has third and fourth resistors 124 for determining a gain between the first operational amplifier 119 and the output terminal. A series circuit consisting of 125 is connected. A first semiconductor switch 127 is connected between the voltage dividing point 126 of the series circuit and the one end of the first resistor 118. Similarly, the second operational amplifier 122 has a positive input terminal grounded, and a negative input terminal connected to one end of the second resistor 121 has a fifth and a sixth for determining a gain between the second operational amplifier 122 and the output terminal. A series circuit composed of resistors 128 and 129 is connected. A second semiconductor switch 132 is connected between the voltage dividing point 131 of the series circuit and the one end of the second resistor 121.

  In this transmission circuit 100, an IC (Integrated Circuit) temperature sensor (Temp) 133 is arranged as a device for detecting temperature. Such a temperature sensor 133 is commercially available from a plurality of manufacturers. The detection output 134 of the temperature sensor 133 is input to the comparison input terminal of the comparator 135.

  The reference voltage input terminal of the comparator 135 receives the voltage at the voltage dividing point 138 of the series circuit composed of the seventh and eighth resistors 136 and 137 having one end connected to a predetermined constant voltage power supply line and the other end grounded. It has become so. The comparison result 139 of the comparator 135 is inverted in logic via the inverter 141 and then input to the first internal control circuit 142 that constitutes an analog switch together with the first semiconductor switch 127, and the first semiconductor switch 127. It is used to control. The comparison result 139 is input to the second internal control circuit 143 that constitutes an analog switch together with the second semiconductor switch 132, and is used to control the second semiconductor switch 132. The output 144 of the second operational amplifier 122 is a control input for the second variable attenuator 108.

  Next, the operation of the transmission circuit 100 having such a configuration will be described. The transmission circuit 100 is used to frequency-convert a modulated wave signal in a IF (Intermediate Frequency) band from a modulator (MODEM) (not shown) to a desired radio frequency and amplify it to a desired transmission output. It is. The transmission signal 101 input to the transmission circuit 100 is attenuated by the first variable attenuator 102 and input to the mixer 104. In the mixer 104, the signal is mixed with the local signal 106 of the local oscillator 105 and up-converted to a desired frequency.

Since the mixer 104 is a non-linear circuit, distortion occurs at this time. IM3 (two-signal third-order intermodulation distortion), which is the third-order distortion in the input level and distortion, is generally in a relationship proportional to one to two. Here, IM3 refers to the second harmonics f ₁ × 2 and f ₂ × 2 generated by nonlinearity when signals of _two frequencies f ₁ and f ₂ are input to a device such as the mixer 104. the two frequencies f _1, f ₂ to be, as a result of two frequency components of the following occurs, refers to a strain generated in these two frequencies f _1, very close portion f _2.
2f ₁ -f ₂ , 2f ₂ -f ₁

  Since the input level and IM3 are in such a proportional relationship, the amount of distortion of IM3 decreases as the input level decreases. However, the level of the local signal 106 input to the mixer 104 does not change. Therefore, the ratio of the amount of leakage of the local signal 106 from the mixer 104 to the transmission signal 107 after up-conversion becomes higher as the input level of the transmission signal 103 to the mixer 104 becomes lower, and the transmission signal 107 deteriorates. become.

  The characteristics of IM3 of the mixer 104 also change depending on the temperature. In a mixer that itself has an amplifying action or a mixer in which an amplifier is arranged in the previous stage, the gain increases and distortion increases as the temperature decreases.

  FIG. 2 shows the relationship between IM3 and temperature. It can be seen that the distortion of IM3 increases when the temperature drops below a predetermined temperature.

  Returning to FIG. 1, the description will be continued. The transmission signal 107 that has been up-converted through the mixer 104 is attenuated through the second variable attenuator 108 and then amplified to a desired output level by the amplifier 110. Then, it is output to the outside through the directional coupler 111. A transmission signal 113 as a part of the transmission output is extracted by the directional coupler 111 and input to the detector 114.

  The detector 114 detects the input signal, and outputs a voltage corresponding to the transmission output level as the detection output 115. The detection output 115 passes through the low-pass filter 116 and is input as an output 117 to the first operational amplifier 119 via the first resistor 118 and to the second operational amplifier 122 via the second resistor 121. Amplified. Then, it is input to the first variable attenuator 102 or the second variable attenuator 108. The series of circuits described above constitutes a feedback loop. For this reason, the signal level of the transmission signal 145 output from the directional coupler 111 to the outside is controlled so as to be always constant regardless of the temperature.

  Next, the detection output 134 of the temperature sensor 133 will be described. This detection output 134 is input to one input terminal of the comparator 135. The voltage at the voltage dividing point 138 of the seventh and eighth resistors 136 and 137 is input to the other input terminal of the comparator 135. The comparator 135 compares these voltages. Then, when the detection output 134 becomes equal to or higher than the voltage at the voltage dividing point 138, the comparison result 139 changes to a high level or a low level. The comparison result 139 is input to the first operational amplifier 119 and the second operational amplifier 122, and the attenuation amounts of the first and second variable attenuators 102 and 108 are switched.

  FIG. 3 shows how the attenuation amounts of the first variable attenuator and the second variable attenuator are switched. In this figure, the vertical axis represents the amount of attenuation (ATT amount), and the horizontal axis represents the change in temperature. In the present embodiment, it is assumed that the comparator 135 shown in FIG. 1 switches the logic level of the comparison result 139 at a temperature of 0 ° C. In the region where the temperature on the right side of the broken line 151 in FIG. 3 is higher than 0 degree C, the attenuation amounts of the first variable attenuator 102 and the second variable attenuator 108 converge to predetermined constant values, respectively. Yes. However, strictly speaking, a gain fluctuation due to temperature occurs and the convergence point is shifted. Therefore, the attenuation amounts of the first and second variable attenuators 102 and 108 are lower right as shown on the right side of the broken line 151 in FIG. It has a temperature gradient.

  When the temperature around the transmission circuit 100 decreases and the temperature sensor 133 detects a temperature of 0 ° C. or lower, the comparison result 139 of the comparator 135 changes from a low level to a high level due to a change in the detection output 134. To do. As a result, the second internal control circuit 143 turns on the second semiconductor switch 132 to reduce the resistance value of the feedback resistor of the second operational amplifier 122 to the resistance value of the fifth resistor 128. The second variable attenuator 108 decreases the attenuation amount by the change of the output 144 of the second operational amplifier 122 by this, and the attenuation amount is a predetermined value lower than the convergence value when the temperature is higher than 0 degrees C. (See FIG. 3).

  When the temperature sensor 133 detects a temperature of 0 ° C. or less and the comparison result 139 of the comparator 135 changes to a high level, the first internal control circuit 142 outputs a low level signal obtained by inverting the logic by the inverter 141. input. Therefore, the first semiconductor switch 127 is turned off as illustrated. As a result, the feedback resistance of the first operational amplifier 119 becomes the sum of the resistance values of the third and fourth resistors 124 and 125. The first variable attenuator 102 increases the attenuation amount due to the change in the output 123 of the first operational amplifier 119 and thereby has a predetermined value whose attenuation is higher than the convergence value when the temperature is higher than 0 degrees C. (See FIG. 3).

  However, even in these cases where the temperature has changed to 0 ° C. or less, gain fluctuation due to temperature occurs and the convergence point is shifted. For this reason, the amount of attenuation of the first variable attenuator 102 and the second variable attenuator 108 has a temperature gradient that falls to the right as shown on the left side of the broken line 151 in FIG.

  In this way, control is performed in which the attenuation amount of the first variable attenuator 102 is decreased and the attenuation amount of the second variable attenuator 108 is increased on the higher temperature side than 0 degrees C as the reference temperature of control. On the other hand, when the temperature becomes 0 degrees C or less, control is performed to increase the attenuation amount of the first variable attenuator 102 and decrease the attenuation amount of the second variable attenuator 108. As described above, since the attenuation amounts of the first and second variable attenuators 102 and 108 change complementarily depending on the temperature, the attenuation amount as a whole does not change greatly over a wide temperature range. In addition, the distortion of IM3 is reduced by reducing the level of the transmission signal 103 input to the mixer 104 at a low temperature (in this example, the temperature range is 0 ° C. or lower, but not limited to this). To balance the IM3 over a wide temperature range.

  FIG. 4 shows a level diagram of the transmission circuit of the present embodiment. FIG. 4A shows changes in signal levels in each circuit portion until a signal input to the transmission circuit 100 shown in FIG. 1 is output. FIG. 5B corresponds to FIG. In addition, the total change of IM3 in each circuit portion is shown. Here, FIG. 5A shows the signal level of each part at room temperature, that is, in the embodiment, 0 ° C. or more.

  FIG. 5 shows a level diagram by the transmission circuit of the present embodiment at a low temperature in comparison with a conventional transmission circuit. FIG. 4A shows changes in signal levels in each circuit portion until a signal input to the transmission circuit 100 shown in FIG. 1 is output. FIG. 5B corresponds to FIG. In addition, changes in the sum total of IM3 in each circuit portion are shown. A solid line indicates the characteristics of the transmission circuit 100 according to the present embodiment, and a broken line indicates a conventional transmission circuit that is not corrected at a low temperature for comparison.

  When a conventional transmission circuit is used, control for changing the attenuation of the transmission signal 101 is not performed in front of the mixer 104. For this reason, as indicated by the broken line, the signal level at a low temperature is higher than that of the present embodiment indicated by the solid line. That is, in the conventional transmission circuit, as a result of inputting a high signal level to the mixer 104 at a low temperature, the total IM3 is deteriorated as shown in FIG.

  On the other hand, in the transmission circuit 100 of the present embodiment, the amount of attenuation of the first variable attenuator 102 before the mixer 104 is relatively large at low temperatures as shown in FIG. The output level at low temperatures is lower than before. Thereby, in this embodiment, excessive input of the transmission signal 103 to the mixer 104 is prevented at low temperatures, and IM3 is prevented from increasing and deteriorating at low temperatures.

  Further, the conventional transmission circuit may be designed so that the signal level of the transmission signal 101 input to the mixer 104 in advance is uniformly lowered over the entire temperature range in order to minimize the increase in IM3 at low temperatures. In this case, the ratio of the amount of leakage of the local signal 106 increases as the signal level of the original transmission signal 101 decreases, and the transmission signal 107 deteriorates, or the overall gain at room temperature becomes insufficient. Will occur.

  In the case of the transmission circuit 100 according to the present embodiment, since the attenuation amount of the first variable attenuator 102 before the mixer 104 is set to be large only at low temperatures, the gain of the transmission signal can be reduced over the entire temperature range. Absent. Further, it is not necessary to set the signal level of the transmission signal 101 input to the mixer 104 low at a low temperature in advance. Therefore, it is possible to prevent deterioration of the transmission signal 107 output from the mixer 104 without increasing the ratio of the amount of leakage of the local signal 106 even at a low temperature.

  As described above in detail, in the present embodiment, the attenuation amount of the variable attenuator is switched depending on the temperature. Thereby, it is possible to maintain a good transmission output without causing deterioration due to distortion in a wide temperature range.

  <First Modification of Invention>

  FIG. 6 shows a transmission circuit according to the first modification of the present invention. In FIG. 6, the same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted as appropriate. In the transmission circuit 100A of the first modification, the two-stage control of the attenuation amount of the first variable attenuator 102 by the output 123A of the first operational amplifier 119 is performed by the first operational amplifier 119 including the feedback resistor 201. This is realized by inputting the comparison result 139 of the comparator 135 via the eleventh resistor 202 to the minus (−) input terminal.

  The output 144A of the second operational amplifier 122 for controlling the attenuation amount of the second variable attenuator 108 is directly performed using the output 117A of the low-pass filter 116. That is, the output 117A of the low-pass filter 116 is input to the minus (−) input terminal of the second operational amplifier 122 connected with the feedback resistor 203 via the twelfth resistor 204.

  In the transmission circuit 100A of the first modification as described above, the temperature sensor 133 detects the temperature of the mixer 104, and the attenuation amount of the first variable attenuator 102 is controlled in two steps according to this. As a result, the signal level of the transmission signal 103 input to the mixer 104 at a low temperature decreases, so that an increase in IM3 can be suppressed to a minimum. In addition, the signal level of the transmission signal 145A output to the outside is variably controlled by adjusting the attenuation amount of the second variable attenuator 108 by the loop after the mixer 104. As a result, the signal level of the transmission signal 145A is kept constant.

  That is, in this first modification, the control by the temperature sensor 133 is simplified compared to the previous embodiment, but the suppression of the increase in IM3 and the signal level of the transmission signal 145A output from the transmission circuit 100A are as follows. An effect almost equivalent to that of the previous embodiment can be obtained.

  <Second Modification of Invention>

  FIG. 7 shows a transmission circuit according to the second modification of the present invention. In FIG. 7, the same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted as appropriate. In the transmission circuit 100B according to the second modification, unlike the transmission circuits 100 and 100A according to the previous embodiment and the first modification, the signal level is controlled digitally. That is, the transmission signal 113 extracted from the directional coupler 111 is input to the detector 114. The analog level detection output 115 is input to the first A / D converter (A / D) 301. The first A / D converter 301 converts a voltage value as a detection output into a digital signal. The transmission output 302 obtained in this way is taken into a bus (not shown) connected to a CPU (Central Processing Unit) 303.

  On the other hand, the detection output 134 of the temperature sensor 133 is input to the second A / D converter 304, and the analog signal is similarly converted into a digital signal. This temperature detection output 305 is also taken into the bus connected to the CPU 303.

  The CPU 303 performs arithmetic processing using the input transmission output 302 and temperature detection output 305, and outputs a first variable attenuator control signal 306 for controlling the attenuation amount of the first variable attenuator 102B. 1 D / A converter (D / A) 307. Further, the second variable attenuator control signal 308 for controlling the attenuation amount of the second variable attenuator 108B is input to the second D / A converter 309. The CPU 303 calculates the first variable attenuator control signal 306 and the second variable attenuator control signal 308 so that the voltage value as the detection output 115 of the detector 114 is constant regardless of the temperature, The amount of attenuation of the first variable attenuator 102B or the second variable attenuator 108B is controlled.

  The first D / A converter 307 converts the first variable attenuator control signal 306 as a digital signal into a first variable attenuator control signal 311 as an analog signal. The first variable attenuator control signal 311 is input to the negative (−) input terminal of the first operational amplifier 119 via the twenty-first resistor 312. The first operational amplifier 119 has a series circuit of twenty-second and twenty-third resistors 313 and 314 connected between its negative input terminal and output terminal. Therefore, the first variable attenuator 102B inputs the output 123B corresponding to the level of the first variable attenuator control signal 306 for control, and varies the attenuation amount.

  On the other hand, the second D / A converter 309 converts the second variable attenuator control signal 308 as a digital signal into a second variable attenuator control signal 315 as an analog signal. The second variable attenuator control signal 315 is input to the negative input terminal of the second operational amplifier 122 via the 24th resistor 316. The second operational amplifier 122 has a 25th and 26th resistors 317 and 318 connected in series between its negative input terminal and output terminal. Therefore, the second variable attenuator 108B inputs the output 144B corresponding to the level of the second variable attenuator control signal 308 for control, and varies the attenuation amount.

  By the way, in the transmission circuit 100B of the second modification, the control amounts of the first variable attenuator control signal 306 and the second variable attenuator control signal 308 are distributed according to the detection output 134 of the temperature sensor 133. It is supposed to change. In the previous embodiment, as shown in FIG. 3, the convergence point of the attenuation amount is switched at a specific temperature such as 0 ° C. For example, in the second modified example, according to the temperature. When the CPU 303 calculates a constant coefficient, it is possible to independently and continuously control the attenuation amounts of the first and second variable attenuators 102B and 108B with respect to the temperature change. In the second modification example, a ROM (Read Only Memory) table (not shown) is prepared, and the temperature detection output 305 is input as address information to the corresponding first variable attenuator control signal 306 and the second. By reading the variable attenuator control signal 308, control of the amount of attenuation that varies depending on such a temperature range is realized.

  FIG. 8 shows the contents of the ROM table for controlling the attenuation in the second modification. The horizontal axis represents the temperature detected by the temperature detection output 305, and the vertical axis represents the first variable attenuator 102B and the first variable attenuator 102B realized by the first variable attenuator control signal 306 and the second variable attenuator control signal 308, respectively. 2 represents the attenuation amount of the variable attenuator 108. Here, the curve 321 represents the operating characteristic of the first variable attenuator 102B, and the curve 322 represents the operating characteristic of the second variable attenuator 108B.

  According to the contents of the ROM table shown in FIG. 8, while increasing the attenuation controlled by the first variable attenuator 102B at a low temperature in a quadratic function, the attenuation of the second variable attenuator 108B is increased. It is decreased so as to be inversely proportional to this. By such non-linear control of the attenuation amount, finer control is possible in the second modification than in the previous embodiment.

  In the second modification, the characteristics of the first and second variable attenuators 102B and 108B are controlled according to the temperature, but the characteristics of the detector 114 may be further corrected by the temperature. That is, in addition to the above-described ROM table for controlling the temperature of the attenuation characteristics of the first and second variable attenuators 102B and 108B, a correction table for the detector 114 is prepared as a ROM, for example. Then, the transmission output 302 after the A / D conversion of the detection output 115 of the detector 114 is used as address information, and the voltage value corrected for the temperature may be read from this ROM and taken into the CPU 303. .

  In this way, not only the temperature characteristics of the mixer 104 but also the temperature characteristics of the detector 114 are corrected, thereby suppressing an increase in IM3 with respect to a temperature change and making the signal level of the transmission signal 145 more accurate. It becomes possible to keep a certain level.

  In the second modification, the ROM table based on the results measured in advance is used to correct the attenuation and the detection characteristic with respect to the temperature. An attenuation amount or other correction amount may be obtained by inputting a value representing the temperature at that time.

  In the embodiment and each modification, the signal level is adjusted using the attenuator, but the present invention is not limited to this. That is, the same effect can be obtained by adjusting the amplification factor in a circuit that requires amplification.

100, 100A, 100B Transmission circuit 101, 145 Transmission signal 102, 102B First variable attenuator 104 Mixer 105 Local oscillator 106 Local signal 108, 108B Second variable attenuator 110 Amplifier 111 Directional coupler 114 Detector 119 First One operational amplifier 122 Second operational amplifier 123, 123A, 144, 144A Output 127 First semiconductor switch 132 Second semiconductor switch 133 Temperature sensor 135 Comparator 303 CPU

Claims (8)

An oscillator,
A mixer that converts the frequency of the input signal by mixing the oscillation output of the oscillator and the input signal;
Temperature detecting means for detecting the temperature of the mixer;
A signal that is disposed in the front stage of the mixer and that relatively reduces the signal level of the input signal in a predetermined temperature range in which distortion of the mixer increases according to the detection result of the temperature detection unit, compared to other regions. Level adjustment means,
The signal level adjusting means controls each of the attenuation amounts in a quadratic function according to a temperature change detected by the temperature detecting means.   Signal level additional adjusting means is provided at a subsequent stage of the mixer and relatively reduces a signal level of a signal output from the mixer in a region other than the predetermined temperature region than in the predetermined temperature region. The signal processing circuit according to claim 1.   3. The signal processing circuit according to claim 2, wherein each of the signal level adjusting means and the signal level additional adjusting means is an attenuator for adjusting an attenuation factor.   3. The signal processing circuit according to claim 2, wherein each of the signal level adjusting means and the signal level additional adjusting means is an amplifier for adjusting an amplification factor.   The output level adjusting means is arranged after the signal level additional adjusting means and adjusts the output level to a constant value regardless of the detection result of the temperature detecting means. 4. The signal processing circuit according to any one of 4 above.   2. The signal processing circuit according to claim 1, wherein the signal after adjustment by the signal level adjusting means is transmitted to the outside.   The signal processing circuit according to claim 1, wherein the input signal is a signal received wirelessly.   2. The signal processing circuit according to claim 1, wherein the mixer has an amplifying function or an amplifier is disposed in front of the mixer.

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