JP2009071376A - Variable gain amplifier circuit and signal switching semiconductor integrated circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a linearity error due to the influence of a base current and a leak current in a VCA circuit having a DA converter for converting a control code for controlling an amplification factor into a voltage even if a bipolar transistor is used as a switch element of the DA converter. To do.
A first amplification / attenuation circuit (11) for amplifying or attenuating an input signal, a second amplification / attenuation circuit (12) for amplifying or attenuating an input signal, a first input terminal and a second input terminal And receiving the signal amplified or attenuated by the first amplification / attenuation circuit at the first input terminal, receiving the signal amplified or attenuated by the second amplification / attenuation circuit at the second input terminal, and receiving the n-bit digital input. Resistor ladder & switch circuit (13) for generating a voltage according to the frequency, and a third amplifying / attenuating circuit for amplifying or attenuating the output or input signal of the second amplifying / attenuating circuit by receiving the output of the circuit at a non-inverting input terminal And a differential amplifier circuit (14) that receives the output of (15) at an inverting input terminal to which a feedback resistor is connected.
[Selection] Figure 1

Description

  The present invention relates to a voltage controlled variable gain amplifier circuit and a signal switching semiconductor integrated circuit incorporating the voltage controlled variable gain amplifier circuit, and more particularly, to a variable gain amplifier circuit having a DA converter circuit having a resistance ladder and a changeover switch and a differential amplifier circuit. Related to effective technology.

  Conventionally, in a system that digitally processes audio signals and video signals, a VCA circuit (voltage controlled variable gain amplifier circuit) is used to amplify a signal received by a tuner and supply it to an AD conversion circuit as a signal having a desired amplitude. It has been. Many VCA circuits control the amplification factor (gain) by voltage. However, in digital signal processing systems, it is convenient if the amplification factor of the VCA circuit can be controlled by a control code from a CPU or the like. Various VCA circuits incorporating a DA conversion function for conversion have been proposed.

FIG. 8 shows a circuit example of a VCA circuit having a DA converter. This VCA circuit includes series ladder resistors R1 to Rn connected between an inverting input terminal of a differential amplifier circuit AMP having a feedback resistor Rf and a ground point, and switch elements SW1 to SWn connected in parallel to the respective resistors. The DA conversion unit controls the amplification factor (gain) of the differential amplifier circuit AMP to amplify the analog signal input to the non-inverting input terminal. In this VCA circuit, the combination (number) of switch elements SW1 to SWn that are turned on is changed according to the control code, and the amplification factor is changed by changing the combined resistance of the series ladder resistor.
JP 2000-341127 A JP 2001-345702 A

  In the VCA circuit of FIG. 8, bipolar transistors or MOSFETs are used as the switch elements SW1 to SWn. When a MOSFET is used, its on-resistance is relatively large, so the number of resistors in the series ladder resistor circuit, that is, the number of control stages (variable range) of the amplification factor cannot be increased too much. Further, since the current flowing through the series ladder resistor is supplied from the output terminal of the differential amplifier circuit, it is not suitable for a low power supply voltage circuit. Therefore, when it is desired to increase the number of gain control stages, it is desirable to use bipolar transistors as the switch elements SW1 to SWn.

  However, when a bipolar transistor is used, the linearity error of the output signal deteriorates as shown in FIG. 9 due to the influence of the base current peculiar to the bipolar transistor and the leakage current at the OFF time. That is, even when the VCA circuit is required to have linearity as shown by the broken line A in FIG. 9, the actual output characteristics are shifted as shown by the solid line B in FIG. 9 due to the influence of the base current and the leakage current. There is a problem that it has many characteristics.

  Furthermore, as a problem of the series ladder resistor circuit, if each resistor is given a weight of 2 to reduce the number of resistors, an error caused by resistance variation is more on the MSB side than on the LSB side. Therefore, the error characteristic of the entire circuit is deteriorated. In order to prevent such deterioration of the error characteristics, it is conceivable to increase the number of resistors and switch elements by making the values of the respective resistors the same. However, by doing so, the number of bits of the control code, that is, the number of control stages of the amplification factor is increased. When there are many, there is a problem that the circuit scale increases significantly.

  Note that there are inventions described in Patent Documents 1 and 2 as DA conversion circuits using a circuit similar to the R-2R ladder resistor circuit used by the VCA circuit of the present invention. The present invention relates to a DA conversion circuit, and these cannot be used as they are in the DA conversion section in the circuit of FIG. 8, and even if configured so as to be usable, the base current and the current when a bipolar transistor is used as a switch element The effect of the present invention to eliminate the influence of the leakage current is not obtained.

  An object of the present invention is to provide a straight line due to the influence of a base current and a leakage current even if a bipolar transistor is used as a switch element of a DA converter in a VCA circuit having a DA converter that converts a control code for controlling an amplification factor into a voltage. It is an object of the present invention to provide a circuit configuration technique capable of reducing the performance error.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a circuit configuration technique for a VCA circuit having a DA converter that converts a control code for controlling an amplification factor into a voltage so that the circuit scale does not increase significantly even if the number of amplification control stages is increased. Is to provide.

  In order to achieve the above object, a variable gain amplifier circuit according to the present invention includes a first amplification / attenuation circuit that amplifies or attenuates an input signal, and a second amplification / attenuation circuit that amplifies or attenuates the input signal; A first input terminal and a second input terminal, the signal amplified or attenuated by the first amplification / attenuation circuit is received by the first input terminal, and amplified or attenuated by the second amplification / attenuation circuit A resistor ladder and switch circuit that receives a signal at the second input terminal and generates a voltage corresponding to an n-bit (n is a positive integer) digital input, and an output of the resistor ladder and switch circuit as a non-inverting input terminal A differential amplifier circuit receiving the output of the second amplifier / attenuator circuit or the output of the third amplifier / attenuator circuit for amplifying or attenuating the input signal at an inverting input terminal connected to a feedback resistor; Configuration to prepare It was.

  The resistor ladder & switch circuit includes n first resistors connected in series between an output point and a constant potential point, a connection point between each of the n first resistors, and the first input. N changeover switches provided between the terminal and the second input terminal, and n provided between the common terminal side of the changeover switch and the connection points of the n first resistors. A second resistor, and the change-over switch transmits a signal of the first input terminal or the second input terminal to the common terminal side according to the n-bit digital input, and the first resistor A voltage obtained by dividing and synthesizing the voltage by a ladder resistor circuit including a second resistor is generated and output from the output point.

  According to the above-described means, a variable gain amplifier circuit is configured in which no current flows from the differential amplifier circuit to the resistor ladder & switch circuit. Therefore, even if a bipolar transistor is used as a switch element in the resistor ladder & switch circuit. The influence of the base current and the leakage current can be eliminated and the linearity error can be reduced.

  Further, the resistance value of the second resistor is set to be twice the resistance value of the first resistor. As a result, the n first resistors and the n second resistors function as an R-2R ladder resistor circuit. Therefore, when the number of amplification control stages is increased by one, the first resistor and the second resistor Since it is only necessary to add one switch and one changeover switch, the circuit scale is not significantly increased.

  Preferably, the feedback resistor is a variable resistor. By changing the resistance value of the variable resistor using non-volatile storage means such as OTP, it becomes possible to adjust circuit characteristics such as offset and variable width of the variable gain amplifier circuit.

  According to the present invention, it is possible to realize a variable gain amplifier circuit that can reduce the linearity error due to the influence of the base current and the leakage current even if a bipolar transistor is used as the switch element of the DA converter. Further, there is an effect that it is possible to realize a variable gain amplifier circuit that does not significantly increase the circuit scale even if the number of control stages of the amplification factor is increased.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an embodiment of a VCA circuit having a DA converter according to the present invention. The VCA circuit of this embodiment includes a first amplification or attenuation circuit 11 that amplifies or attenuates the input signal Vin, a second amplification or attenuation circuit 12 that amplifies or attenuates the input signal Vin, and a first amplification or attenuation. A resistor ladder & switch circuit 13 that receives the signal amplified or attenuated by the circuit 11 and the signal amplified or attenuated by the second amplifier or attenuation circuit 12, and the output of the resistor ladder & switch circuit 13 as a non-inverting input terminal And receiving the output of the second amplifying or attenuating circuit 12 at the inverting input terminal via the input resistor Ri, and being connected between the output terminal and the inverting input terminal of the differential amplifying circuit 14. And feedback resistor Rf.

  The first amplifying or attenuating circuit 11 and the second amplifying or attenuating circuit 12 may be configured such that both are amplifying circuits or both are attenuating circuits, and one is an amplifying circuit and the other is an attenuating circuit. is there.

  FIG. 2 shows a specific circuit example of the resistor ladder & switch circuit 13. The resistor ladder & switch circuit 13 of this embodiment includes a first input terminal IN1 that receives the output of the first amplification or attenuation circuit 11, and a second input terminal that receives the output of the second amplification or attenuation circuit 12. IN, n resistors (n is a positive integer) R1, R2, R3... Rn connected in series between the ground point and the output terminal OUT, and n selector switches SW1, SW2, SW3. ... SWn and n resistors R11, R12 connected between the common-side terminals of these changeover switches and the connection nodes N1, N2, N3... Nn of the resistors R1, R2, R3. , R13... R1n.

  The two switching terminals SW1, SW2, SW3... SWn are selectively connectable to the first input terminal IN1 and the second input terminal IN2, respectively. The switch is controlled by n-bit control codes B1 to Bn, and either signal of the input terminal IN1 or IN2 is input to the corresponding resistor (R11, R12, R13... R1n) according to the state of each bit. . Thereby, the resistor ladder & switch circuit 13 transmits the signal of the first input terminal or the second input terminal to the common side terminals of SW1 to SWn, and the ladder resistor composed of the resistors R1 to Rn and R11 to R1n. The circuit generates a divided and synthesized voltage according to the control code and outputs it from the output terminal OUT.

  When the resistance values of the resistors R2, R3... Rn are r, the resistance values of the resistors R11, R12,... R1n are doubled to 2r. As a result, the resistor ladder & switch circuit functions as a circuit similar to the R-2R resistor ladder circuit in the known DA converter circuit when a fixed voltage is applied to the input terminals IN1 and IN2, and the amplification factor is increased. It operates as a DA converter that converts control codes R1 to Rn to be controlled into voltages. The change-over switches SW1, SW2,... SWn are each composed of two switch elements (transistors) that are turned on and off in a complementary manner.

  FIG. 3 shows a specific circuit example of the amplifier circuit used in the amplifier or attenuation circuits 11 and 12, and FIG. 4 shows a specific circuit example of the attenuation circuit. 3 includes a differential amplifier circuit AMP1, a resistor Ri1 connected between the inverting input terminal of the differential amplifier circuit AMP1 and the ground, and an output terminal and an inverting input terminal of the differential amplifier circuit AMP1. And a feedback resistor Rf1 connected between the two. 4 includes a buffer BFF1 and a resistor Rd1 connected between the input terminal and the output terminal, and a buffer BFF2 and a resistor Rd2 connected between the ground point GND and the output terminal. . The buffer BFF2 is for lowering the impedance and can be omitted.

  In the VCA circuit of FIG. 1, the gain of the first amplifying or attenuating circuit 11 is Av1, the gain of the second amplifying or attenuating circuit 12 is Av2, and the gain of the amplifying or attenuating circuits 11 and 12 and the resistor ladder & switch circuit 13 is Av3. The gain Av of the entire circuit is given by

Av = {Av2 *-(Rf / Ri)} + {Av3 * (Rf + Ri) / Ri}
It is represented by The gain Av3 can be obtained using Thevenin's theorem.

  From the above equation, it can be seen that the gain Av of the VCA circuit of this embodiment is independent of the current value. Therefore, even if bipolar transistors are used as the changeover switches SW1, SW2,... SWn in the resistor ladder & switch circuit 13, the circuit gain Av is not affected by the base current and the leakage current. 1 is compared with FIG. 8, in FIG. 8, the output of the resistor ladder circuit is connected to the output terminal via the feedback resistor of the differential amplifier circuit 14, whereas in FIG. It is clear from the fact that the output of the ladder & switch circuit 13 is connected to the non-inverting input terminal of the differential amplifier circuit 14 having a high input impedance. That is, the current flows from the differential amplifier circuit to the resistor ladder circuit in the VCA circuit of FIG. 8, whereas the current does not flow from the differential amplifier circuit to the resistor ladder circuit in the VCA circuit of FIG. On the circuit, it seems that there is a current path from the output terminal of the differential amplifier circuit 14 to the input terminal IN2 of the resistor ladder & switch circuit 13, but the current is the current supply capability of the second amplifier or attenuation circuit 12. Is sufficiently small so that it can be regarded as “0”.

In the VCA circuit of FIG. 8, when n increases by “1”, it is necessary to increase the number of resistors and switch elements by (2 ^{n + 1} −2 ⁿ ), whereas in the VCA circuit of FIG. Even when “1” increases, the resistance of the resistance value r and the resistance of the resistance value 2r can be increased by one and the number of switches (two transistors) can be increased. Much less.

  Further, the VCA circuit of this embodiment is more advantageous when the change-over switches SW1, SW2,... SWn in the resistor ladder & switch circuit 13 are made of bipolar transistors than when the switches are made of MOSFETs. The reason is that the bipolar transistor has a smaller on-resistance than the MOSFET, so that the potential accuracy of the nodes N1 to Nn in the R-2R resistor ladder circuit is higher and the bipolar transistor is more accurate. This is because the operation is performed even when the level of the signal input to the resistance ladder & switch circuit 13 is low. Further, when a circuit having better characteristics can be obtained by using a bipolar transistor as an element constituting the amplifier circuit of the differential amplifier circuit 14 or the amplifiers or attenuator circuits 11 and 12, a changeover switch in the resistor ladder & switch circuit 13 is obtained. Also, the bipolar transistor is advantageous in that the process can be simplified and the manufacturing cost can be reduced.

In the VCA circuit of FIG. 1, n = 8, that is, the control code is 8 bits, Av1 = 1, Av2 = 0.5, Ri = 6 kΩ, Rf = 9 kΩ, R1 = R2 =... = Rn = 10 kΩ, R11 Considering the case of = R12 =... = R1n = 20 kΩ, it is derived from the Thevenin's theorem that the gain Av3 can be varied in 256 steps within the range of 0.5 to 1.0. Therefore,
The gain Av of the entire circuit is

Av = (0.5 × −1.5) + (0.5 to 1.0 × 2.5) = 0.5 to 1.75
Thus, it can be seen that it can be varied in 256 steps within the range of 0.5 to 1.75.

  FIG. 5 shows a first modification of the VCA circuit according to the embodiment. The VCA circuit of the first modified example is configured such that the resistors Ri and Rf provided in the differential amplifier circuit 14 in the VCA circuit of FIG. 1 are composed of variable resistors, and the first amplifier or attenuation circuit 11 and the second amplifier or The resistors Ri1 and Rf1 in the amplifier circuit and the resistors Rd1 and Rd2 in the amplifier circuit shown in FIG. 3 and FIG. 4 used for the attenuation circuit 12 are configured by variable resistors, and an OTP (fuse cut type read only memory) is formed. It is provided so that the value of each resistor can be adjusted by the set value stored in the OTP.

  The VCA circuit according to the first modification has an advantage that the circuit characteristics such as offset and variable width can be finely adjusted by individually determining the resistance values of the resistors. Note that the setting value may be stored using a non-volatile memory such as a flash memory or an EEPROM instead of the OTP. In the OTP and EEPROM, the characteristics of the VCA circuit are measured at the final stage of the manufacturing process, a value to be corrected so as to obtain a desired characteristic is determined, and the value is stored and shipped at the factory shipping stage.

  FIG. 6 shows a second modification of the VCA circuit according to the embodiment. In the embodiment of FIG. 1, the output of the second amplifier or attenuation circuit 12 is distributed and input to the resistance ladder & switch circuit 13 and the inverting input terminal of the differential amplifier circuit 14, whereas the modification of FIG. The third amplifying or attenuating circuit 15 for generating a signal to be input to the inverting input terminal of the differential amplifying circuit 14, separately from the second amplifying or attenuating circuit 12 for generating the signal to be input to the resistance ladder & switch circuit 13. Is different.

  The gain Av of the entire circuit of this modified example is given by the following equation when the gain of the third amplification or attenuation circuit 15 is Av4:

Av = {Av4 × − (Rf / Ri)} + {Av3 × (Rf + Ri) / Ri}
It is represented by From this equation, even in the VCA circuit of the second modified example, even if bipolar transistors are used as the changeover switches SW1, SW2,... SWn in the resistor ladder & switch circuit 13, the circuit gain Av is the base current or It can be seen that the influence of the leakage current can be avoided.

  Further, in the second modified example, the gain Av4 is appropriately set to set the offset, which is the circuit characteristic, to a desired value, and the gain Av3 (Av1, Av2) is appropriately set to set the variable width to a desired range. Can be. In the first modification, if Av2 is adjusted and the offset is set to a desired value, Av3 (Av1, Av2) also changes and the variable width also changes, so it is troublesome to optimize both simultaneously. In the second modified example, there is an advantage that it is easy to optimize the offset and the variable width separately because adjusting Av4 does not affect Av3 (Av1, Av2). In addition, according to the second modification, the output terminals of the differential amplifier circuit 14 and the resistor ladder & switch circuit 13 as well as the input terminals are completely cut off, and the resistor ladder & switch circuit 13 is switched from the differential amplifier circuit 14. The current flowing in can be set to “0”.

  Although not shown in the drawing, in the VCA circuit of the second modification of FIG. 6, the resistors Ri and Rf provided in the differential amplifier circuit 14 and the first amplification are provided as in the first modification. It is also conceivable that the resistors in the or attenuation circuit 11, the second amplification or attenuation circuit 12, and the third amplification or attenuation circuit 15 are configured by variable resistors so that the characteristics can be adjusted.

  FIG. 7 shows an application example of the VCA circuit of the modification of FIG. This application example is a system that digitally processes audio signals and video signals to obtain a signal having a desired amplitude by amplifying a broadcast signal received by a tuner, and to output a broadcast signal and a signal from a video tape recorder or DVD. The present invention is applied to a signal switching semiconductor integrated circuit (hereinafter referred to as a signal switching IC) used for switching to supply to an AD conversion circuit and converting it to a digital signal.

  The signal switching IC 20 of this application example selects the received signal from the antenna terminal T1 connected to the antenna, amplifies the signal output from the tuner 30 for detection, and outputs the signal as a signal having a desired amplitude. VCA circuit 10 and a signal at video terminal T2 to which a signal amplified by VCA circuit 10 or a signal from a video tape recorder is input, or a signal at DVD terminal T3 to which a signal from DVD is input are selected. Then, a signal changeover switch 25 that supplies the AD conversion circuit 40 in the subsequent stage (outside the chip) is provided.

  The signal switching IC 20 also switches a signal supplied from a terminal 26 that outputs a signal selected by the signal switching switch 25 and control means (hereinafter referred to as a CPU) 50 such as an external microprocessor or microcomputer. A terminal 27 for receiving a control signal of the switch 25, an OTP circuit 28 for setting an adjustment value of resistance in the VCA circuit 10, and the like are provided.

  Reference numerals 21 to 23 denote external terminals of the chip for receiving signals from the terminals T1 to T3 of the device, respectively. When a writable nonvolatile semiconductor memory 29 such as an EEPROM or a flash memory is used instead of the OTP 28 as means for storing a set value for adjusting the resistance value, it is provided as an external element connected to the CPU 50. May be.

  The tuners used in the above application systems have characteristic variations that occur in the manufacturing stage, and it is difficult to supply a stable signal to the AD conversion circuit. Therefore, the characteristic variation of the tuner to be used is measured, and the adjustment value of the resistance in the VCA circuit 10 is determined in accordance therewith, and is set in the OTP circuit 28 or the non-volatile semiconductor memory 29 in the chip. Therefore, it is possible to supply a stable signal that is not affected by the above to the AD conversion circuit.

  Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments. For example, in the above-described embodiment, it has been described that it is particularly effective to use bipolar transistors as the changeover switches SW1, SW2,... SWn in the resistor ladder & switch circuit 13, but it is also possible to use a MOSFET as the changeover switch. In that case, there is no problem of increase in linearity error due to the influence of base current and leakage current inherent to bipolar transistors, and the number of amplification control stages should be increased without significantly increasing the circuit scale. The effect of being able to be obtained.

  In the above-described embodiment, an example in which a fuse-cut type read-only memory is used as a nonvolatile storage means (OTP circuit) for storing a resistance adjustment value in the VCA circuit 10 has been described. In addition to using fuses or the like, a ROM of a type that stores data by selectively melting or melting the interlayer insulating film corresponding to the eyes of the ROM with a laser beam to electrically connect or disconnect the upper and lower conductive layers. Any storage means can be used as long as it can store data after manufacturing.

  In the above description, the case where the invention made mainly by the present inventor is applied to a VCA circuit that amplifies a video signal, which is a field of use as a background, has been described. However, a VCA circuit that amplifies a signal received in a wireless communication system. It can also be used.

FIG. 1 is a block diagram showing an embodiment of a VCA circuit having a DA converter according to the present invention. FIG. 2 is a circuit diagram showing a specific example of a resistance ladder & switch circuit. FIG. 3 is a circuit diagram showing a specific example of an amplifier circuit used in the amplifier or attenuation circuit. FIG. 4 is a circuit diagram showing a specific example of an attenuation circuit used in the amplification or attenuation circuit. FIG. 5 is a block diagram showing a first modification of the VCA circuit according to the embodiment. FIG. 6 is a block diagram showing a second modification of the VCA circuit according to the embodiment. FIG. 7 is a block diagram showing an application example of the VCA circuit of the first modification of FIG. FIG. 8 is a circuit diagram showing an example of a conventional VCA circuit having a DA converter. FIG. 9 is a graph showing characteristics of the VCA circuit of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 1st amplification or attenuation circuit 12 2nd amplification or attenuation circuit 13 Resistance ladder & switch circuit 14 Differential amplification circuit 15 3rd amplification or attenuation circuit 20 Signal switching IC
21 to 23 External terminal 25 Signal changeover switch 26, 27 External terminal 28 OTP (fuse cut type read only memory)
29 Writable non-volatile memory 30 Tuner 40 AD conversion circuit 50 Control means (microcomputer, CPU)

Claims (10)

A first amplification / attenuation circuit for amplifying or attenuating an input signal;
A second amplification / attenuation circuit for amplifying or attenuating the input signal;
A first input terminal and a second input terminal, the signal amplified or attenuated by the first amplification / attenuation circuit is received by the first input terminal, and amplified or attenuated by the second amplification / attenuation circuit A resistor ladder & switch circuit that receives a signal at the second input terminal and generates a voltage corresponding to an n-bit (n is a positive integer) digital input;
A feedback resistor receives the output of the resistor ladder & switch circuit at a non-inverting input terminal, and outputs the output of the second amplification / attenuation circuit or the output of a third amplification / attenuation circuit that amplifies or attenuates the input signal. A differential amplifying circuit received via an input resistor at the connected inverting input terminal,
The resistor ladder & switch circuit
N first resistors connected in series between the output point and the constant potential point;
N number of change-over switches respectively provided between a connection point of each of the n number of first resistors and the first input terminal and the second input terminal;
N second resistors provided between the common terminal side of the changeover switch and the connection points of the n first resistors,
The change-over switch transmits a signal of the first input terminal or the second input terminal to the common terminal side according to the n-bit digital input, and is divided by a ladder resistor circuit including the first resistor and the second resistor. A variable gain amplifier circuit configured to generate a voltage and a combined voltage and output the voltage from the output point. 2. The variable gain amplifier circuit according to claim 1, wherein a resistance value of the second resistor is set to twice a resistance value of the first resistor. 3. The variable gain amplifier circuit according to claim 1, wherein each of the changeover switches is composed of a bipolar transistor. 4. The variable gain amplifier circuit according to claim 1, wherein the input resistor and the feedback resistor are configured by variable resistors. The first amplifying / attenuating circuit or / and the second amplifying / attenuating circuit are connected between a inverting input terminal and a constant potential point and between a inverting input terminal and an output terminal. 5. The variable gain amplifier circuit according to claim 4, comprising a differential amplifier circuit having a feedback resistor, wherein the resistor and the feedback resistor of the differential amplifier circuit are configured by a variable resistor. The first amplifying / attenuating circuit or / and the second amplifying / attenuating circuit include a buffer and a resistor connected in series between an input terminal and an output point, and between the output point and a ground point. 5. The variable gain amplifier circuit according to claim 4, wherein the variable gain amplifier circuit is constituted by a variable resistor. 7. The variable gain amplifier circuit according to claim 4, wherein the variable resistor is configured to be set so as to have a resistance value corresponding to a value stored in a nonvolatile storage means. . 7. The variable gain amplifier circuit according to claim 4, wherein a signal from a tuner is input, and any one of an output of the variable gain amplifier circuit or a signal supplied from a plurality of external devices. A signal switching semiconductor integrated circuit, characterized in that a changeover switch for selecting one is formed on one semiconductor chip. 9. The signal switching semiconductor integrated circuit according to claim 8, wherein a nonvolatile memory means capable of storing a value for determining a resistance value of a variable resistor in the variable gain amplifier circuit is formed on the semiconductor chip. circuit. 9. The signal switching semiconductor integrated circuit according to claim 8, wherein an external terminal for externally providing a value for determining a resistance value of a variable resistor in the variable gain amplifier circuit is provided in the semiconductor chip. circuit.

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