JPH1013169A - Amplification factor monitor circuit of gilbert-type amplification factor variable amplifier and amplification factor monitor system of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly monitor the amplification factor of a Gilbert-type amplification factor variable amplifier with simple configuration by providing an amplification factor monitor circuit, formonitoring the amplification factor of the Gilbert-type amplification factor variable amplifier. SOLUTION: The amplification factor monitoring circuit 100 for monitoring the amplification factor of the Gilbert-type amplification factor variable amplifier 4 includes a differential transistor pair to which a current is supplied from a constant- current source M12 and which respective control signals for controlling the amplification factor of the Gilbert-type amplification factor variable amplifier 4 are inputted. Moreover, a monitor output terminal 110 for outputting the current which is outputted from one transistor within the differential transistor pair is provided. Even with this kind of simple circuit configuration, a monitor current I is obtained with a monitor output terminal 110, and the amplification factor is correctly obtained. When the constant-current source M12 is constituted by resistance by which a constant voltage circuit and aresistance value are not easily changed, the current I12 becomes stable with respect to the change of temp. and a power source voltage and the fluctuation of a process condition, so that the amplification factor is obtained more correctly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for monitoring the gain of a Gilbert-type variable gain amplifier, and more particularly to a circuit for accurately monitoring the gain with a simple configuration.

[0002]

2. Description of the Related Art First, a conventional Gilbert variable gain amplifier and a method of monitoring the gain will be described with reference to FIGS.

FIG. 2 shows a circuit diagram of a Gilbert-type variable gain amplifier. In this circuit, a differential signal input terminal 20, 21 for inputting a differential signal (V1) is connected to an input MOSFET pair M1, M2 connected to a gate terminal, and the input M
A constant current source M3 connected to the source terminal of the OSFET pair
(Current I ₃ ), and the differential signal input terminal 20, according to the differential gain control signal V 3 (VCH, VCL) given via the differential gain control signal input terminals 23 and 24 provided therein. 21 for amplifying the differential signal by changing the amplification factor of the differential signal V1 given via
OSFET pair (amplification control MOSFET pair a and MOSFET M8, comprising MOSFET pair M6 and M7)
M9, a pair of amplification control MOSFETs b), differential signal output terminals 27 and 28 for outputting the amplified differential signal V2, output MOSFET pairs M10 and M11 connected to the drain, and the input MOSFET A constant current source M4 (current I ₄ ) and a current source M5 (current I ₅ ) for supplying current to the pair and the two amplification factor control MOSFET pairs.

[0004] One end of each of the constant current sources M4 and M5 is connected to a power supply line of the power supply voltage VDD, and one end of the constant current source M3 and a pair of output MOSFETs M10 and M1.
One source terminal is connected to the ground voltage VSS line.

Further, currents flowing through the input MOSFET pairs M1 and M2 are I ₁ and I ₂ , respectively.
Assuming that the currents flowing through the FET pair a and the amplification rate control MOSFET pair b are I ₆₇ and I ₈₉ , respectively, according to Kirchhoff's law, “I ₄ = I ₁ + I ₆₇ ” and “I ₅ = I ₂ + I ₈₉ ”. , “I ₄ = I ₅ ” and the differential signal input V1 is “0”
At this time, the circuit is configured such that “I ₆₇ = I ₈₉ ”.

The first control signal VCL is applied to the gates of the gain control MOSFETs M6 and M9, and the second control signal VCH is applied to the gain control MOSFETs M6 and M9.
7, applied to the gate of M8 to control the amplification factor,
The second control signal VCH is applied so as to be always higher than the first control signal VCL.

[0007] When a differential signal is input to the differential signal input terminals 20 and 21, differential amplification is performed by the pair of amplification control MOSFETs a and b, and
The amplified differential signal is output MOSFET pair M10, M
11, a differential signal output terminal 27 connected to the drain of
28.

The amplification factor of the differential amplification is changed by two types of differential amplification factor control signals V3 (VCH, VCL) provided through the differential amplification factor control signal input terminals 23 and 24. The outline will be described with reference to FIG.

FIG. 3 shows a gain control MOS in a Gilbert-type variable gain amplifier for easy understanding.
FET pair a (M6, M7), MOSFET for controlling amplification factor
Only the circuit section related to the pair b (M8, M9) is shown.
Now, the manner in which the amplification factor changes depending on how the first control signal VCL and the second control signal VCH are applied will be described.

FIG. 3A shows a case where "VCL = VCH". When the differential signal V1 is input, I ₈₉ increases by 2Δ and I ₆₇ decreases by 2Δ. As a result, the currents flowing through M8 and M9 are both “+ Δ”,
The currents flowing through M6 and M7 are both “−Δ”, and the point a
The current value at the point b is “0”, and the voltage output via the differential signal output terminals 27 and 28 is “0”, so that the amplification factor is the minimum value, that is, “−∞”.

Next, FIG. 3B shows a case where VCH is much larger than VCL, that is, “VCH≫VCL”. When the differential signal V1 is input, I ₈₉ becomes “2Δ”.
Increasing and decreasing I ₆₇ by “2Δ”, M7,
M8 is turned off, and as a result, the currents flowing through M8 and M9 become “0” and “+ 2Δ”, respectively, and the currents flowing through M6 and M7 become “−2Δ” and “0”, respectively.
The current values at point b are “−2Δ” and “+ 2Δ”, respectively.
The amplification factor becomes the maximum value (Amax).

FIG. 3C shows a case where VCH is larger than VCL, that is, “VCH> VCL”.
When the differential signal V1 is input, I ₈₉ increases by “2Δ”,
When I ₆₇ decreases by “2Δ”, M6 has a lower resistance than M7 and M9 has a lower resistance than M8. As a result, the current flowing through M8 and M9 is, for example, “+
(1/2) · Δ ”and“ + (3/2) · Δ ”, and M
6. The current flowing through M7 is “− (3/2) · Δ”,
The current values at the points a and b are “−Δ” and “+ Δ”, respectively, and the amplification factor is between the maximum value (Amax) and the minimum value. Value.

As described above, the amplification factor changes depending on the magnitudes of the two types of differential amplification factor control signals V3 (VCH, VCL) provided through the differential amplification factor control signal input terminals 23, 24.

It is known that the amplification factor A of the circuit shown in FIG. 2 is approximately given by the following equation (1). A = (gmin / gmload) · ((VCH−VCL) / Von) (1)

Here, "gmin" is the input MOSFE
The transconductance of T versus M1, M2, "gmloa
"d" is the mutual conductance of the output MOSFET pair M10, M11, and "Von" is the differential signal V1 of "0 (V)".
In the case of the amplification factor control MOSFET “M6, M7, M
8, M9 "and the threshold voltage of each transistor. Here, M
6, M7, M8 and M9 are MOSFETs manufactured to have the same structure. "Gmin", "gmloa"
Since “d” and “Von” are fixed values depending on the circuit configuration, conventionally, in order to obtain the amplification factor of the Gilbert-type amplification variable amplifier, the differential amplification factor control signals VCH and VCL are given. Thus, by applying the equation (1), the gain of the variable gain amplifier is directly obtained.

[0016]

However, the gain of the Gilbert-type variable gain amplifier varies greatly due to a minute difference between the differential gain control signals VCH and VCL. "Von"
And so on, the relationship between the amplification factor and the control voltage cannot be unambiguously determined, that is, the relationship between A and “VCH−VCL” is not determined by the equation (1), and the differential amplification factor control is not performed. Signal VC
There is a problem that the gain of the Gilbert-type variable gain amplifier cannot be accurately obtained from H and VCL.

For example, "gmin / gmload = 1"
0, Von = 200 (mV), "VCH-V
CL = 20 (mV) ", A = 0 (dB),
When “VCH−VCL = 22.4 (mV)”, A = 1
(DB). Thus, even if a difference of only 2.4 (mV) occurs in the value of “VCH-VCL”, the amplification factor differs by 1 (dB), and the amplification factor could not be obtained accurately. .

Further, as described above, since the value of Von or the like greatly changes according to changes in process conditions or temperature, it is necessary to uniquely determine the relationship between "VCH-VCL" and the amplification factor A. However, the amplification rate could not be determined accurately.

Further, there is no way to integrally obtain the amplification factors of the plurality of Gilbert-type variable gain amplifiers. The operator obtains the amplification factors of the respective Gilbert-type variable gain amplifiers, and based on the obtained gains, obtains the plurality of Gilbert-type variable gain amplifiers. Since the gain of the variable rate amplifier was determined, the accuracy of the determined gain was very poor.

Therefore, an object of the present invention is to provide a simple configuration,
An object of the present invention is to provide a circuit for accurately monitoring the gain of a Gilbert-type variable gain amplifier. Another object of the present invention is to provide a system for accurately and integrally obtaining the gains of a plurality of Gilbert-type variable gain amplifiers.

[0021]

According to the first aspect of the present invention, there is provided an input transistor pair having a differential signal input terminal for inputting a differential signal, and a differential transistor provided in the input transistor pair. Amplifying the differential signal by changing the amplification factor of the differential signal input through the differential signal input terminal in accordance with the differential control signal supplied through the dynamic amplification control signal input terminal; And a transistor pair for controlling the amplification factor of
An output transistor pair having a differential signal output terminal for outputting an amplified differential signal; and a constant current source for supplying current to the input transistor pair and the two sets of amplification factor control transistor pairs. A Gilbert-type variable gain variable amplifier, and a gain monitor circuit for monitoring the gain, further comprising: a differential transistor pair for inputting the differential control signal; and the differential transistor A gain of a Gilbert-type variable gain amplifier having a configuration including a constant current source for supplying a current to the pair, and a monitor output terminal for outputting a current output from one of the transistors constituting the differential transistor pair. A monitor circuit is provided.

According to a second aspect of the present invention, in the first aspect of the present invention, the supply current of the constant current source included in the amplification rate monitor circuit is controlled by the first current included in the Gilbert type variable amplification rate amplifier. A gain monitor circuit for a Gilbert-type variable gain amplifier, characterized in that the supply current is set to a predetermined number times the supply current supplied to the set of gain control transistor pairs.

According to a third aspect of the present invention, there is provided a Gilbert-type variable gain amplifier and a plurality of gain monitoring circuits according to any one of the first and second aspects. Circuit pair group, an adder for adding the output currents from the monitor output terminals of each set, a current-to-voltage conversion circuit for converting the addition result to a current-to-voltage value, and an amplification factor for the current-to-voltage-converted addition power result. , And an output unit that outputs the operation result, and an amplification factor monitoring system of a Gilbert-type variable amplification factor amplifier is provided.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a gain monitor circuit of a Gilbert-type variable gain amplifier according to an embodiment of the present invention.

This circuit has a Gilbert-type variable gain amplifier 4 and an amplification-rate monitor circuit for monitoring the gain of the Gilbert-type variable gain amplifier 4. The Gilbert-type variable gain amplifier 4 is the same as that shown in FIG.

That is, the Gilbert-type variable gain amplifier 4
Is an input MOSFE in which differential signal input terminals 20 and 21 for inputting a differential signal (V1) are connected to gate terminals.
T pair M1 and M2, a constant current source M3 (current I ₃ ) connected to the source terminal of the input MOSFET pair, and one set given via its own differential amplification factor control signal input terminals 23 and 24 Differential gain control signal V3 (VCH, VC
L), two amplification factor control MOSFET pairs (MOS) for changing the amplification factor of the differential signal V1 provided through the differential signal input terminals 20 and 21 and amplifying the differential signal.
Amplification control MOSFET consisting of FET pair M6 and M7
An output MOSFET pair M10 having a drain connected to a pair a and a pair of amplification control MOSFETs b) including MOSFET pairs M8 and M9, and differential signal output terminals 27 and 28 for outputting an amplified differential signal V3. , M11 and the input MOSFET pair and the two sets of amplification factor control Ms.
OSFET pair constant current source for supplying a current to M4 (current I _4), having an M5 (current I _5), a. One ends of the constant current sources M4 and M5 are connected to the power supply line of the power supply voltage VDD, and one end of the constant current source M3 and the source terminals of the output MOSFET pair M10 and M11 are connected to the ground voltage VSS line. It is connected.

The currents flowing through the input MOSFET pairs M1 and M2 are denoted by I ₁ and I ₂ , respectively.
Assuming that the currents flowing through the FET pair a and the amplification rate control MOSFET pair b are I ₆₇ and I ₈₉ , respectively, according to Kirchhoff's law, “I ₄ = I ₁ + I ₆₇ ” and “I ₅ = I ₂ + I ₈₉ ”. , “I ₄ = I ₅ ” and the differential signal input V1 is “0”
At this time, the circuit is configured such that “I ₆₇ = I ₈₉ ”.

The first differential control signal VCL is applied to the gates of the gain control MOSFETs M6 and M9, and the second differential control signal VCH is applied to the gain control MOSFET.
The second differential control signal VCH is applied to the gates of the FETs M7 and M8 to control the amplification factor, and is applied so as to be always larger than the first differential control signal VCL. When a differential signal is input to the differential signal input terminals 20 and 21, the pair of amplification control MOSFETs a and the pair of amplification control M
The differential signal is differentially amplified by the OSFET pair b, and the amplified differential signal is output via differential signal output terminals 27 and 28 connected to the drains of the output MOSFET pair M10 and M11.

The amplification factor monitor circuit 100 controls the control signal V
A differential MOSFET pair M1 for inputting each of CL and VCH
3, M14 and the power supply line of the power supply voltage VDD.
Supply current to the differential MOSFET pair M13 and M14.
Constant current source 12 (current I ₁₂) And the differential MOSF
One MOSFET constituting the ET pair, specifically, M
The current (I) output from the OSFET (M14)_MOut)
Monitor output terminal 110 and MOSFET
The load 50 is connected to the drain terminal of (M13).
And the other terminal of the load is connected to the ground power VSS line
It is connected to the. Further, the first control signal VCL and the second
Control signals VCH of the MOSFET, M13, M1
4 can be applied to the gate terminal.

Further, as described above, in the Gilbert-type variable gain amplifier 4, the differential signal V1 is "0 (V)".
At the time of MOSFET (M6) and MOSFET
(M7) and the sum of the currents flowing through the MOSFET (M8) and the MOSFET (M9) are equalized. Further, the current flowing through the constant current source M12 is set to "0 (V) Is equal to the sum of the currents flowing through the MOSFET (M6) and the MOSFET (M7),
In addition, MOSFET (M8) and MOSFET (M
9), the following relational expression is obtained between the current flowing through the MOSFET (M14) and the gain Gain (dB) by an equivalent circuit analysis.
In this specification, detailed mathematical expressions using equivalent circuit analysis will not be listed because they hinder understanding, and only the analysis results will be described. Gain (dB) = Gfull (dB) + 20log ((√ (1-β) -√β) / (√ (1-β) + √β)) (2) where Gfull (dB) is Gilbert-type amplification Variable rate amplifier 4
Of the input MOSFET M1, M2
2 and the output MOSFET pair M1
0, the ratio of the transconductance of M11, and
"Β" is the current flowing through the current I ₁₂ flowing through the current source M12 in the case of a "1", the MOSFET (M14) (I _M)
Is the value of The value of Gfull (dB) is stable against changes in temperature, power supply voltage, and process.

Β is the value of the monitor current (I _M ) when the current I ₁₂ flowing through the constant current source M12 is “1” (ie, “I ₁₂ : I _M = 1: β”), current I ₁₂ flowing through the constant current source M12, the change in temperature and power supply voltage, because with respect to variations in process conditions are stable, the monitor current (I _M)
Can be obtained from.

Therefore, even with such a simple circuit configuration, the monitor current ( _IM ) is obtained via the monitor output terminal 110, and by using the equation (2), the gain of the Gilbert-type variable gain amplifier 4 is obtained. Will be determined exactly. Further, the constant current source M12, if configured with hardly changes resistance constant voltage circuit and the resistance value, temperature and supply voltage changes, to variations in process conditions, current I ₁₂ becomes stable, more accurately amplification factor Is found.

Equation (2) is always established between β and the amplification factor (Gain (dB)).
The amplification factor of the Gilbert-type variable gain amplifier, which could not be obtained stably with respect to changes in temperature and power supply voltage, and process fluctuations, can be stably changed with temperature and power supply voltage changes and process fluctuations. You can ask.

If "Gfull (dB) = 0", a graph showing the relationship between β and Gain (dB) determined by equation (2) is as follows.
As shown in FIG. As can be seen from this graph, unless β is near “0”, between β and logarithmic amplification factor (Gain (dB)) in the range of β up to 0.4 except for β. Approximately, a linear relationship is established.

Therefore, in order to guarantee a linear relationship until β is close to “0”, the current I ₁₂ flowing through the constant current source M ₁₂ is controlled by the amplification factor control when the differential signal V 1 is 0 (V). MOSFET pair a (or amplification factor control MOSF)
MOSFET, M6 and M7 constituting ET pair b)
(Or MOSFETs, M8 and M9), a predetermined multiple of the sum of the currents flowing through the MOSFETs, for example, a value in the range of about 1 to 1.5 times, when the β is in the range of 0 to 0.4, MO
A monitor current (I _M ) flowing through the SFET (M14);
A linear relationship is approximately established between the amplification factor (Gain (dB)) in logarithmic display, and the value of the monitor current (I _M ) is obtained with a simple circuit configuration to obtain the amplification factor in logarithmic display. (Ga
in (dB)) can be easily obtained. Note that the expression “about 1 to 1.5 times” is based on a simulation result by a simulation tool performed by the inventors.

FIG. 4 shows a circuit configuration for displaying and outputting the obtained amplification factor. This circuit comprises a Gilbert-type variable gain variable amplifier 4, a gain monitor circuit 100 for outputting a monitor current corresponding to the gain, an IV converter 115 for current / voltage conversion of the monitor current, and an analog / digital conversion of the converted voltage. AD converter 1 for conversion (AD conversion)
20; a microcomputer 130 which receives a digital signal and calculates an amplification factor according to the equation (2); and a display 140 which displays a result of the calculation.

The microcomputer 130 has a ROM in which a calculation program is built in advance, a RAM that functions as a work area, and a CPU that performs various processes such as calculation processing in accordance with the program built in the ROM. The display 140 can be realized by a display element such as a 7-segment LED or a display device such as a CRT. Note that the IV converter 115 and the AD converter 120 may employ known circuits. In such a circuit configuration, the microcomputer 130 performs the current-voltage conversion by the IV converter 115,
An amplification factor calculation is performed on the converted digital signal according to equation (2). Then, the display 140 displays the calculation result of the amplification factor, so that the operator can immediately grasp the amplification factor. Of course, by employing the Gilbert-type variable gain amplifier 4 according to the present invention and the gain monitor circuit 100, the gain can be stably obtained even when there is a change in temperature, power supply voltage, or process variation. be able to.

FIG. 5 shows a circuit configuration of another embodiment. This circuit is composed of a plurality of circuit pairs (41, 101, and 4) including a Gilbert-type variable gain amplifier and a gain monitor circuit that outputs a monitor current corresponding to the gain.
2 and 192, 43 and 103,..., 4i and 10i), an adder 150 for adding the monitor currents output from each circuit pair, an IV converter 115 for current / voltage conversion of the added monitor currents, An AD converter 120 that performs analog-to-digital conversion (AD conversion) of the converted voltage, a microcomputer 130 that receives a digital signal and calculates an amplification factor in accordance with Equation (2), and a display that displays the calculation result And a vessel 140.

As shown in the figure, the monitor currents output from each circuit pair are denoted by I _M1 , I _M2 , I _M3 ,..., I _Mi. The microcomputer 130 is realized by a ROM having a built-in arithmetic program in advance, a RAM functioning as a work area, and a CPU performing various processes such as arithmetic processing in accordance with the program built in the ROM. it can.

The display unit 140 as an output unit has a
It can be realized by a display element such as a segment LED or a display device such as a CRT or a liquid crystal display. Furthermore, another output device (output unit) such as a printing device may be provided instead of the display device 140.

The adder 150, the IV converter 115, and the AD converter 120 may employ known circuits. In such a circuit configuration, the microcomputer 130 converts the result obtained by adding the monitor currents output from each circuit pair by the IV converter 115 into a current-to-voltage conversion.
The gain of the digital signal subjected to AD conversion by the AD converter 120 is calculated according to the equation (2). Then, the display 140 displays the calculation result of the amplification factor, so that the operator can immediately grasp the amplification factor of the entire circuit pair at a time, and amplify the integrated circuit pair. It is possible to immediately determine the rate and immediately grasp the existence of an abnormal circuit pair. The number of circuit pairs may be any number as long as it is two or more. In this case, the configuration of the adder 150 may be changed according to the number of circuit pairs. Specifically, the adder 150 may be configured to have the number of addition input terminals equal to the number of circuit pairs.

It is also preferable to provide a measurement terminal 158 capable of directly measuring the addition result of the adder 150 as a measurement current, since the amplification factor can be immediately measured and operated, for the convenience of the operator's measurement operation.

Further, in this embodiment, MOSFET pairs are employed as various transistor pairs.
It goes without saying that other transistor pairs such as a BT pair and various FET pairs other than the MOS type may be employed.

[0044]

As described above, according to the first aspect of the present invention, a Gilbert-type amplification factor monitoring circuit for monitoring the amplification factor of a Gilbert-type variable gain amplifier is supplied with current from a constant current source. It has a configuration including a differential transistor pair for inputting each of the control signals for controlling the amplification factor of the amplification factor variable amplifier, and further has a monitor output terminal for outputting a current output from one transistor of the differential transistor pair. With this configuration, it is possible to realize a circuit capable of accurately monitoring the gain of the Gilbert-type variable gain amplifier with a simple circuit configuration.

According to the second aspect of the present invention, in addition to the effect of the first aspect, a linear relationship exists between a change in monitor current output from the monitor output terminal and a logarithmic amplification factor. As a result, a circuit capable of monitoring the amplification factor more accurately can be realized.

Further, according to the third aspect of the present invention, in addition to the effects of the first or second aspect of the present invention, the first aspect of the present invention provides the following advantages.
And a circuit pair group comprising a plurality of sets of the Gilbert-type variable gain amplifier and the gain monitor circuit according to any one of 2 and 2, the adder adds the output current from the monitor output terminal of each set, The arithmetic circuit obtains the amplification factor with respect to the added voltage result obtained by converting the addition result into a current voltage, and the output unit outputs the calculation result. Therefore, the amplification factors of the plurality of Gilbert-type amplification variable variable amplifiers are accurately and integrally obtained. The system can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram according to an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a Gilbert-type variable gain amplifier.

FIG. 3 is an explanatory diagram of the operation of a Gilbert-type variable gain amplifier.

FIG. 4 is a configuration diagram of another embodiment.

FIG. 5 is a configuration diagram of another embodiment.

FIG. 6 is an explanatory diagram showing a relationship between β, which is a parameter indicating a magnitude of a monitor current flowing through a MOSFET (M12), and an amplification factor.

[Explanation of symbols]

 Reference Signs List 4 Gilbert-type variable gain amplifier 20 Differential signal input terminal 21 Differential signal input terminal 23 Differential gain control signal input terminal 24 Differential gain control signal input terminal 27 Differential signal output terminal 28 Differential signal output terminal 41 Gilbert-type variable gain factor amplifier 42 Gilbert-type variable gain factor amplifier 43 Gilbert-type variable gain factor amplifier 4i Gilbert-type variable gain factor 50 Load 100 Gain monitor circuit 101 Gain monitor circuit 102 Gain monitor circuit 103 Gain monitor circuit 10i Amplification rate monitor circuit 110 Monitor output terminal 115 IV converter 120 A / D converter 130 Microcomputer 140 Display 150 Adder 158 Measurement terminal

Claims (3)

[Claims] An input transistor pair having a differential signal input terminal for inputting a differential signal; and a differential control signal supplied via a differential amplification factor control signal input terminal provided therein. Two pairs of amplification factor control transistors for amplifying the differential signal by changing the amplification factor of the differential signal input via the differential signal input terminal, and the difference for outputting the amplified differential signal A Gilbert-type variable gain amplifier including: an output transistor pair having a dynamic signal output terminal; a constant current source that supplies current to the input transistor pair and the two pairs of gain control transistor pairs; And a gain monitor circuit for monitoring, the gain monitor circuit comprising: a differential transistor pair for inputting the differential control signal; a constant current source for supplying current to the differential transistor pair; And a monitor output terminal for outputting a current output from one of the transistors forming the differential transistor pair, the gain monitor circuit for a Gilbert-type variable gain amplifier. 2. The power supply according to claim 1, wherein the supply current of a constant current source included in the amplification factor monitor circuit is supplied to a pair of amplification factor control transistor pairs included in the Gilbert type variable amplification factor amplifier. A gain monitor circuit for a Gilbert-type variable gain amplifier, characterized in that the current is set to a predetermined number of times. 3. A circuit pair group comprising a plurality of Gilbert-type variable gain amplifiers and a plurality of gain monitor circuits according to claim 1 and an output current from a monitor output terminal of each set is added. A Gilbert type including an adder, a current-to-voltage conversion circuit for current-to-voltage conversion of the addition result, an operation circuit for obtaining an amplification factor for the current-to-voltage conversion addition result, and an output unit for outputting the operation result Gain control system for variable gain amplifier.