JP4585461B2 - Variable gain amplifier - Google Patents

Description

  The present invention relates to an amplification factor variable amplifier that is configured by a MOS transistor or the like and that can change an amplification factor (gain) and can suppress fluctuations in the amplification factor due to temperature.

2. Description of the Related Art In recent years, for example, variable gain amplifiers used in mobile communication devices such as mobile phones have been developed using MOS transistors that are advantageous for cost reduction and high integration.
In addition, variable gain amplifiers used in mobile communication devices are provided with various temperature compensation circuits because the same quality is required even if the temperature fluctuates. For example, a variable gain amplifier as described in Patent Document 1 is known as a prior art.

The amplifier described in Patent Document 1 is configured by a MOS circuit, and realizes temperature compensation of the Gilbert variable gain amplifier by using a bias source generally called a gm constant bias. .
Specifically, as shown in FIG. 5, this conventional amplifier includes a Gilbert variable gain amplifier 1, a bias circuit 2, and a control circuit 3.

The Gilbert gain variable amplifier 1 includes input MOS transistors M1 and M2 constituting a differential pair, gain control MOS transistors M3 and M4 constituting a differential pair, and gain control constituting a differential pair. MOS transistors M5 and M6, a MOS transistor 10 functioning as a current source, and resistors R1 and R2 serving as output loads.
The bias circuit 2 is a circuit that variably controls the bias current flowing through the MOS transistor M10, and includes MOS transistors M11 to M16 and a resistor R3.

The control circuit 3 supplies a gain control voltage to each gate of the MOS transistors M3 to M6 in order to control the gain of the Gilbert gain variable amplifier 1.
The gain Gain of the variable gain amplifier having such a configuration can be expressed by the following formula (1), and can be finally expressed by formula (3) by referring to formula (2). .

Where Vout is an output signal, Vin is an input signal, I1 is a current flowing through a transistor connected to the output load of the amplification factor control transistor pair, I0 is a total current flowing through the amplification factor control transistor pair, Rload is an output load, gm0 represents the mutual conductance of the input transistor pair. Here, (I0-I1) is a current flowing through the other transistor of the amplification factor control transistor pair.
Accordingly, the Gilbert gain variable amplifier realizes variable amplification by controlling the ratio of dI1 / dI0 described above with the gate voltage of the gain control transistor pair.

By the way, in the Gilbert type variable gain amplifier, in the region where the gain is near the maximum setting, I1≈I0, I1 / I0≈1, and dI1 / dI0 = 1 = constant.
Similarly, in the region where the gate voltages of the amplification factor control transistor pair are equal, I1≈I0 / 2, I1 / I0≈I0 / (2 × I0) = 1/2, and dI1 / dI0 = 1/2 = Since it is a constant, the effect of the gain control transistor pair due to the temperature hardly affects the gain Gain.

Therefore, in the region where the temperature change of dI1 / dI0 (T) can be ignored, the temperature dependency of the amplification factor depends on the product of gm0 and Rload, and this gm × Rload as a current source as in the prior art. By using a constant Gm bias that keeps constant with respect to temperature, it is possible to realize temperature compensation of the amplification factor.
JP 2004-343212 A

  However, in the conventional circuit as described above, for example, when the control signal is set to the minimum amplification factor, the temperature characteristic of dI1 / dI0 (T) of the amplification factor control transistor becomes dominant in the amplification factor Gain. For this reason, the effect of the amplification factor control transistor pair represented by dI1 / dI0 (T) cannot be ignored, and accurate temperature compensation cannot be performed within a wide variable gain range.

Therefore, when the gain is controlled in a region where the temperature characteristic is constant, the gain control range is greatly limited. Therefore, the appearance of a new circuit capable of performing temperature compensation with high accuracy while having a large amplification factor control range is desired.
Accordingly, an object of the present invention is to provide an amplification factor variable amplifier that can realize temperature compensation of an amplification factor in a wide variable amplification factor range in view of the above points.

In order to solve the above problems and achieve the object of the present invention, the present invention has the following configuration .

A first invention is an amplification variable amplifier including a Gilbert gain variable amplifier, an amplification monitor circuit, and an amplification compensation signal generation circuit, wherein the Gilbert amplification variable amplifier is a differential amplifier. An input transistor pair for inputting a signal, two amplification factor control transistor pairs for amplifying the differential signal by changing the amplification factor according to the inputted amplification factor control signal, and an amplified differential An output load for outputting a signal, a first current source for supplying a predetermined current to the input transistor pair, and a current to the input transistor pair, respectively, and the sum of the supply currents of the first current source A second current source and a third current source equal to the current, and a fourth current source and a fifth current source capable of supplying current to the two sets of amplification factor control transistor pairs and varying the supply current, amplification Monitor circuit includes: the corresponding to the amplification factor control transistor pair, its addition to monitoring the change in the amplification factor with temperature in the gain control transistors, the amplification factor monitor transistor pair having a gate and a drain connected to one of the transistors, the amplification factor and supplies the current to the monitor transistor pair, a sixth current source that supplies current can be changed, the current supplied to the sixth current source to the drain of the one transistor of the transistor pair gain monitor A seventh current source capable of supplying a current of a predetermined fractional times and varying the supply current, and the amplification factor compensation signal generation circuit includes a differential voltage between input terminals of the amplification factor monitoring transistor pair; A differential operational amplifier that compares a predetermined reference differential voltage without temperature dependence and generates an amplification factor compensation signal according to the difference; and 4, 5, each supply current of the sixth and seventh current source is adapted to vary with the gain compensation signal generated by the amplification factor compensation signal generation circuit.

In a second aspect based on the first aspect , the amplification factor compensation signal generation circuit further comprises a first MOS transistor that allows a predetermined current to flow in accordance with the amplification factor compensation signal output from the differential operational amplifier. 4, 5, 6, and 7 of the current source, the second, third, and a fourth, and fifth MOS transistors, said first, second, third, and fourth MOS The transistor forms a predetermined current mirror circuit.

The third invention is the second invention, a sixth MOS transistor forming the first 4 MOS transistor and a predetermined current mirror circuit to flow a predetermined current to said sixth MOS transistor, before Symbol first 5 MOS transistors and a seventh MOS transistor forming a predetermined current mirror circuit, and the sixth MOS transistor has a predetermined ratio to the transistor size of the fourth MOS transistor. The seventh MOS transistor has a predetermined ratio with respect to the transistor size of the fifth MOS transistor.
In a fourth aspect based on the first , second or third aspect , the Gilbert variable gain amplifier comprises a folded Gilbert variable gain amplifier.

  According to the present invention, amplification factor temperature compensation can be realized in a wide variable amplification factor range.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a block diagram showing a configuration of a first embodiment of a variable gain amplifier according to the present invention.
As shown in FIG. 1, the first embodiment includes a Gilbert gain variable amplifier 11, an gain monitor circuit 12, and an gain compensation signal generation circuit 13, and the amplification of the Gilbert gain variable amplifier 11. Temperature compensation of the rate.

The Gilbert variable amplification factor amplifier 11 includes an input terminal 21, a control terminal 22, and an output terminal 23, amplifies the input signal IN input to the input terminal 21, and an amplification factor control signal Vc applied to the control terminal 22. Accordingly, the amplification factor of the input signal IN is varied (controlled).
In the Gilbert variable gain amplifier 11, the operating current (bias current) related to the gain is controlled by the gain compensation signal Sc generated by the gain compensation signal generation circuit 13, and the gain is temperature compensated. It has become so.

  The amplification factor monitor circuit 12 is composed of a dummy amplification factor variable amplifier (dummy circuit) that is arranged close to the Gilbert amplification factor variable amplifier 11 and has the same temperature characteristics, and its operating current (bias current) is the Gilbert amplification factor. This is the same type as the variable amplifier 11. For this reason, the gain characteristics of the gain monitor circuit 12 are the same as those of the Gilbert variable gain amplifier 11.

That is, the gain monitor circuit 12 is equivalent to a predetermined circuit included in the Gilbert variable gain amplifier 11 and is configured by a circuit having a predetermined gain. A voltage corresponding to the change in the operating current is generated, and this is output as an output voltage Vout to the amplification factor compensation signal generation circuit 13.
Furthermore, the amplification factor monitor circuit 12 is controlled in its operating current (bias current) by the amplification factor compensation signal Sc generated by the amplification factor compensation signal generation circuit 13, and the amplification factor is controlled to be constant (temperature compensation). It is like that.

The amplification factor compensation signal generation circuit 13 compares the output voltage Vout from the amplification factor monitor circuit 12 with a predetermined reference voltage Vref from a reference voltage source (not shown) having no temperature dependency, and according to the difference. An amplification factor compensation signal Sc is generated and supplied to the Gilbert type variable amplification factor amplifier 11 and the amplification factor monitor circuit 12, respectively.
Next, an operation example of the first embodiment having such a configuration will be described.

The amplification factor monitor circuit 12 generates a voltage corresponding to a change in the amplification factor due to a change in temperature (a change in its own operating current due to the temperature), and uses this generated voltage as an output voltage Vout to the amplification factor compensation signal generation circuit 13. Supply.
The amplification factor compensation signal generation circuit 13 compares the output voltage Vout with a reference voltage Vref having no temperature dependency, and generates an amplification factor compensation signal Sc according to the difference, which is combined with the Gilbert gain variable amplifier 11 and the amplification. Each is supplied to the rate monitor circuit 12.

As a result, the gain compensation signal Sc controls the operating current of the Gilbert gain variable amplifier 11 and simultaneously controls the operating current of the gain monitor circuit 12.
Here, for example, the same voltage as the output voltage Vout from the gain monitor circuit 12 is input to the control terminal 22 of the Gilbert gain variable amplifier 11 as the gain control signal Vc. If the operating current of the Gilbert variable gain amplifier 11 and the operating current of the gain monitor circuit 12 are the same type and equivalent, the Gilbert variable gain amplifier 11 has a predetermined gain of the gain monitor circuit 12. The input signal is amplified and output at the same amplification factor as the amplification factor.

As described above, in the first embodiment, the output voltage Vout of the amplification factor monitor circuit 12 is compared with the reference voltage Vref of the reference voltage source independent of temperature, and the Gilbert type amplification is performed so that these two voltages are the same. The same type of operating current of the variable rate amplifier 11 and the gain monitor circuit 12 is controlled.
For this reason, as long as the reference voltage Vref generated by the reference voltage source is the same as the control voltage Vc of the Gilbert variable gain amplifier 11, the gain of the Gilbert variable variable amplifier 11 is the gain monitor under any temperature condition. It becomes the same as the predetermined amplification factor of the circuit 12, and the temperature characteristic of the amplification factor is compensated.
In the first embodiment, the reference voltage Vref of the reference voltage source can be arbitrarily determined. By selecting the reference voltage Vref in a region where d1 / d0 (T) is maximized, Then, temperature compensation can be performed in a region where temperature compensation could not be performed.

(Second Embodiment)
FIG. 2 is a circuit diagram showing a configuration of the second embodiment of the variable gain amplifier according to the present invention.
In the second embodiment, the configuration of each part of the first embodiment shown in FIG. 1 is embodied. As shown in FIG. 2, a Gilbert variable gain amplifier 11, a gain monitor circuit 12, An amplification factor compensation signal generation circuit 13 is provided, and temperature compensation of the amplification factor of the Gilbert variable amplification factor amplifier 11 is performed.
As shown in FIG. 2, the Gilbert gain variable amplifier 11 includes a pair of MOS transistors M1 and M2 for input, a pair of MOS transistors M3 and M4 for gain control, and a pair of MOS for gain control. Transistors M5 and M6, current source S1, current sources S2 and S3, variable current sources S4 and S5, and output loads R1 and R2 are provided.

  The MOS transistors M1 and M2 constitute a differential pair, and a differential input signal is supplied to the gates thereof. The MOS transistors M3 and M4 and the MOS transistors M5 and M6 constitute two sets of differential pairs, amplify the above input signals, and according to the differential gain control signals input to the gates thereof. The amplification factor of the differential input signal can be controlled.

The output loads R1 and R2 function to output an amplified differential input signal.
The current source S1 supplies a predetermined operating current to the MOS transistors M1 and M2. The current sources S2 and S3 are configured to supply predetermined currents to the corresponding MOS transistors M1 and M2, respectively, and the sum of the supply currents is equal to the supply current of the current source S1. Here, as shown in FIG. 2, the current sources S1, S2, and S3 are constant current sources, but may be configured with variable current sources.

The variable current source S4 supplies an operating current to the MOS transistors M3 and M4, and the supply current is varied by an amplification factor compensation signal output from the amplification factor compensation signal generation circuit 13.
Similarly, the variable current source S5 supplies an operating current to the MOS transistors M5 and M6, and the supply current is varied by the amplification factor compensation signal output from the amplification factor compensation signal generation circuit 13. .

  More specifically, the MOS transistors M1 and M2 have their gates connected to the input terminals 31 and 32, their sources connected in common, and the common connection portion grounded via the current source S1. The drain of the MOS transistor M1 is connected to the power supply terminal 37 via the current source S2. The drain of the MOS transistor M2 is connected to the power supply terminal 37 via the current source S3.

  In the MOS transistors M3 and M4, the gates are connected to the control terminals 33 and 34, the sources are connected in common, the common connection is connected to the drain of the MOS transistor M1, and the variable current source S4 is used. Is grounded. The drain of the MOS transistor M3 is connected to the output terminal 36 and to the power supply terminal 37 via the load resistor R1. The drain of the MOS transistor M4 is connected to the power supply terminal 37.

  In the MOS transistors M5 and M6, the gates are connected to the control terminals 34 and 33, the sources are connected in common, the common connection is connected to the drain of the MOS transistor M2, and the variable current source S5 is used. Is grounded. The drain of the MOS transistor M5 is connected to the power supply terminal 37. The drain of the MOS transistor M6 is connected to the output terminal 35 and is connected to the power supply terminal 37 via the load resistor R2.

As shown in FIG. 2, the gain monitor circuit 12 includes a pair of MOS transistors M7 and M8 for monitoring the gain, a variable current source S6, and a variable current source S7.
The MOS transistors M7 and M8 correspond to the MOS transistors M3 and M4 (or the MOS transistors M5 and M6) of the Gilbert type variable gain amplifier 11 and have the same type and the same temperature characteristics as the MOS transistors M3, M4, This is for monitoring the change in amplification factor due to the temperature of M4.

The variable current source S6 supplies current to the MOS transistors M7 and M8, and the supply current is varied by the amplification factor compensation signal output from the amplification factor compensation signal generation circuit 13.
The variable current source S7 supplies current to the MOS transistor M7, and the supply current is varied by the amplification factor compensation signal output from the amplification factor compensation signal generation circuit 13. The variable current source S7 supplies a current that is a predetermined fraction times the supply current of the variable current source S6.

More specifically, the gate of the MOS transistor M7 is connected to its own drain and to the input terminal of the differential operational amplifier 131 of the amplification factor compensation signal generation circuit 13. The drain of the MOS transistor M7 is connected to the power supply terminal 37 via the variable current source S7.
The gate of the MOS transistor M8 is connected to the input terminal of the differential operational amplifier 131 and a predetermined voltage is applied thereto. The drain of the MOS transistor M8 is connected to the power supply terminal 37. The sources of the MOS transistors M7 and M8 are connected in common, and the common connection is grounded via the variable current source S6.

As illustrated in FIG. 2, the amplification factor compensation signal generation circuit 13 includes a differential operational amplifier 131.
The differential operational amplifier 131 compares the differential voltage output from the amplification factor monitor circuit 12 with a differential reference voltage from a constant voltage source (not shown), and generates an amplification factor compensation signal according to the difference. The generated gain compensation signal is supplied to the variable current sources S4, S5, S6, and S7, respectively. Thereby, each current of the variable current sources S4, S5, S6, and S7 is controlled.

Next, the operation of the second embodiment having such a configuration will be described.
The amplification factor of the Gilbert variable gain amplifier 11 of the second embodiment having such a configuration can be expressed by the following equation (4) with reference to the above equation (3).

  In the equation (4), I1 is a current flowing through the MOS transistor M3, I0 is a sum of currents flowing through the MOS transistors M3 and M4, Rload is a value of the output load R1, and gm0 is a mutual conductance of the MOS transistors M1 and M2. Here, (I0-I1) is a current flowing through the MOS transistor M4.

In the second embodiment, current sources S1, S2, and S3 and variable current sources S4 and S5 are provided, and the operating currents of the MOS transistors M1 and M2 are supplied by the current sources S1, S2, and S3, and the variable current sources S4, S5 are supplied. Thus, the MOS transistors M3 and M4 and the MOS transistors M5 and M6 are caused to flow operating currents, respectively, so that both operating currents can be controlled for each temperature effect.
That is, the temperature effect of gm0 depends on the current source S2, and the temperature effect of dI1 / dI0 depends on the variable current sources S4 and S5. Therefore, gm0 and dI1 / dI0 can be controlled by separate operating currents.

Therefore, in the second embodiment, the amplification factor compensation signal generation circuit 13 compares the output voltage from the amplification factor monitor circuit 12 with the reference voltage of the reference voltage source having no temperature dependence, and performs amplification according to the difference. A rate compensation signal is generated, and the operation current supplied from the variable current sources S4 and S5 of the Gilbert gain variable amplifier 11 is controlled by the generated signal.
For this reason, the Gilbert variable gain amplifier 11 can realize an amplification factor in which the current ratio I1 / I0 does not depend on the temperature with respect to the reference voltage of the reference voltage source, and the amplification factor Gain is expressed by the following equation (5). Can be represented.

  In the second embodiment, the current I1 supplied from the variable current source S7 of the amplification factor monitor circuit 12 to the MOS transistor M7 is a predetermined fractional multiple 1 / N of the current I0 supplied from the variable current source S6 to the entire circuit. I tried to become. Therefore, the current ratio I1 / I0 of the amplification factor monitoring circuit 12 is a predetermined fractional multiple 1 / N, and dI1 / dI0 = 1 / N = constant. This current ratio I1 / I0 determines the amplification factor of the amplification factor monitor circuit 12.

  Further, since dI1 / dI0 of the amplification factor monitoring circuit 12 is a constant, the current ratio of the amplification factor monitoring MOS transistors M7 and M8 has no temperature dependency. The voltage difference between the amplification factor monitoring MOS transistors M7 and M8 indicates a voltage for making the current ratio I1 / I0 constant with respect to the current supplied from the variable current source S6. At the same time, the potential difference indicates a voltage for making the gain of the gain monitor circuit 12 constant.

  In the second embodiment, the differential operational amplifier 131 compares the voltage difference obtained from the amplification factor monitoring MOS transistors M7 and M8 with the reference voltage of the reference voltage source having no temperature dependency. Then, the output of the differential operational amplifier 131 controls the currents of the variable current sources S6 and S7 so that the amplification factor monitor circuit 12 outputs the same voltage as the given reference voltage. As a result, the current ratio of the MOS transistors M7 and M8 is kept constant.

Further, the reference voltage of the reference voltage source used here and the predetermined fractional multiple 1 / N have a temperature dependency of the current ratio I1 / I0 of the Gilbert variable gain amplifier 11 in the absence of the gain monitor circuit 12. It is desirable to select a voltage that will be the maximum region.
In the second embodiment, a resistor is used as an output load as shown in FIG. 2, but an output load composed of an inductor, a transistor, or the like may be used.

  In the second embodiment, as shown in FIG. 2, the Gilbert variable gain amplifier 11 is composed of an N-type MOS transistor, but instead of this, a P-type MOS transistor is used. Anyway. In that case, it is necessary to use the same type of P-type MOS transistors as the MOS transistors constituting the amplification factor monitor circuit 12. At the same time, the connection of each current source, output load, etc. is changed from the power supply terminal to the ground and from the ground to the power supply terminal.

(Third embodiment)
FIG. 3 is a circuit diagram showing the configuration of the third embodiment of the variable gain amplifier of the present invention.
In the third embodiment, the Gilbert gain amplifier 11 of the first embodiment shown in FIG. 1 is replaced with a Gilbert variable gain amplifier 11A having a folded structure as shown in FIG.
Since the configuration of the third embodiment is the same as that of the second embodiment shown in FIG. 2 except for the Gilbert variable gain amplifier 11A, the same components are denoted by the same reference numerals, and the description thereof is omitted. Is omitted.

The Gilbert variable gain amplifier 11A according to the third embodiment is folded at the drain point of a pair of input MOS transistors, and individually controls the operating current of each MOS transistor.
That is, as shown in FIG. 3, the Gilbert variable gain amplifier 11A includes a pair of MOS transistors M21 and M22 for input, a pair of MOS transistors M3 and M4 for gain control, and a pair for gain control. MOS transistors M5 and M6, a current source S11, current sources S12 and S13, variable current sources S14 and S15, and output loads R1 and R2.

  The MOS transistors M21 and M22 constitute a differential pair, and a differential input signal is supplied to the gates thereof. The MOS transistors M3 and M4 and the MOS transistors M5 and M6 constitute two sets of differential pairs, amplify the above differential input signals, and respond to the differential gain control signals input to the gates thereof. Thus, the gain of the input signal can be controlled.

The output loads R1 and R2 function to output an amplified differential input signal.
The current source S11 supplies current to the MOS transistors M21 and M22. The current source S12 supplies current to the MOS transistor M21, and the current source S13 supplies current to the MOS transistor M22.

The variable current source S14 supplies current to the MOS transistors M3 and M4, supplies current to the MOS transistor S21, and the supply current is variable according to the amplification factor compensation signal output from the amplification factor compensation signal generation circuit 13. It has come to be.
The variable current source S15 supplies current to the MOS transistors M5 and M6 and also supplies current to the MOS transistor S22, and the supplied current is varied by the amplification factor compensation signal output from the amplification factor compensation signal generation circuit 13. It is like that.

  More specifically, MOS transistors M21 and M22 have their gates connected to input terminals 31 and 32, their sources connected in common, and their common connection connected to power supply terminal 37 via current source S11. Yes. The drain of the MOS transistor M21 is grounded via the current source S12. The drain of the MOS transistor M22 is grounded through the current source S13.

  In the MOS transistors M3 and M4, the gates are connected to the control terminals 33 and 34, the sources are connected in common, the common connection is connected to the drain of the MOS transistor M21, and via the variable current source S14. Is grounded. The drain of the MOS transistor M23 is connected to the output terminal 36 and to the power supply terminal 37 via the load resistor R1. The drain of the MOS transistor M24 is connected to the power supply terminal 37.

In the MOS transistors M5 and M6, the gates are connected to the control terminals 34 and 33, the sources are connected in common, the common connection is connected to the drain of the MOS transistor M22, and via the variable current source S15. Is grounded. The drain of the MOS transistor M5 is connected to the power supply terminal 37. The drain of the MOS transistor M6 is connected to the output terminal 35 and to the power supply terminal 37 via the load resistor R2.
In the third embodiment having such a configuration, the same operation as that of the second embodiment can be realized, and the same effect as that can be realized.

(Fourth embodiment)
FIG. 4 is a circuit diagram showing the configuration of the fourth embodiment of the variable gain amplifier according to the present invention.
In the fourth embodiment, each current source of the constituent elements of the third embodiment shown in FIG. 3 is constituted by a MOS transistor as shown in FIG.
Since the configuration of the fourth embodiment is the same as that of the third embodiment shown in FIG. 3 except for the current source configured by the MOS transistor, the same components are denoted by the same reference numerals and Description is omitted.
In the fourth embodiment, the current sources S11, S12, and 13 shown in FIG. 3 are configured by MOS transistors M23, M24, and M25 as shown in FIG. 4, and the gates of the MOS transistors M23, M24, and M25 are connected to the gates. A predetermined bias voltage was applied to each.

Further, the variable current sources S6, S7, S14, and S15 shown in FIG. 3 are configured using MOS transistors M31 to M38 as shown in FIG.
That is, the MOS transistor 31 causes a predetermined current to flow according to the amplification factor compensation signal output from the differential operational amplifier 131, and this current is supplied to the MOS transistor M32.

  The MOS transistor 32 forms a first current mirror circuit with the MOS transistors M33 to M36, and currents proportional to the current flowing through the MOS transistor 32 flow through the MOS transistors M33 to M36, respectively. The current of the MOS transistor 32 and the current flowing through the MOS transistors M33 to M36 can be determined by the transistor size.

  The current flowing through the MOS transistor M34 flows through the MOS transistor M37. The MOS transistor M37 forms a second current mirror circuit with the MOS transistor M38, and a current proportional to the current flowing through the MOS transistor 37 flows through the MOS transistor M38. The current of the MOS transistor 37 and the current flowing through the MOS transistor M38 can be determined by the transistor size.

According to the fourth embodiment having such a configuration, the current ratio of the current source consisting of the MOS transistor M33 and the current source consisting of the MOS transistor M38 can be realized by the transistor size (W / L size) ratio of the MOS transistor. Therefore, a current that is a predetermined fraction times as high can be obtained with high accuracy.
In the fourth embodiment, the size ratio between the MOS transistors M35 and M36 for current source of the Gilbert variable gain amplifier 11 and the pair of MOS transistors M3 and M4 (M5 and M6) and the gain monitor If the ratio of the magnitudes of the current source MOS transistor M33 and the pair of MOS transistors M7 and M8 in the circuit 12 is equal, the magnitude of the current of the current source can be arbitrarily selected.

  The variable gain amplifier of the present invention is applied to a variable gain amplifier used in various ICs, and can be mounted, for example, in a wireless communication device, and can compensate for variations in gain due to temperature.

It is a block diagram which shows the structure of 1st Embodiment of this invention. It is a circuit diagram which shows the structure of 2nd Embodiment of this invention. It is a circuit diagram which shows the structure of 3rd Embodiment of this invention. It is a circuit diagram which shows the structure of 4th Embodiment of this invention. It is a circuit diagram of a conventional variable amplification factor amplifier.

Explanation of symbols

11 Gilbert type variable gain amplifier 11A Folded structure Gilbert variable gain amplifier 12 Amplification monitor circuit 13 Amplification compensation signal generation circuit

Claims (4)

A gain variable amplifier including a Gilbert gain variable amplifier, an amplification monitor circuit, and an amplification compensation signal generation circuit,
The Gilbert variable gain amplifier is
An input transistor pair for inputting a differential signal;
Two amplification factor control transistor pairs for changing and amplifying the differential signal according to an input amplification factor control signal;
An output load for outputting an amplified differential signal;
A first current source for supplying a predetermined current to the input transistor pair;
A second current source and a third current source, each supplying current to the pair of input transistors, the sum of the supply currents being equal to the current of the first current source;
A fourth current source and a fifth current source capable of supplying current to the two amplification factor control transistor pairs, respectively, and changing the supply current;
The amplification factor monitor circuit includes:
Corresponding to the amplification factor control transistor pair, and monitoring the change of the amplification factor due to the temperature of the amplification factor control transistor, an amplification factor monitoring transistor pair to which the gate and drain of one transistor are connected,
A sixth current source capable of supplying a current to the amplification factor monitoring transistor pair and changing the supply current;
A seventh current source capable of supplying a current that is a predetermined fraction of a current supplied by the sixth current source to the drain of the one transistor of the amplification factor monitoring transistor pair, and capable of varying the supply current;
The amplification factor compensation signal generation circuit compares the differential voltage between the input terminals of the amplification factor monitoring transistor pair with a predetermined reference differential voltage having no temperature dependence, and compensates the amplification factor according to the difference. It has a differential operational amplifier that generates signals,
The supply currents of the fourth, fifth, sixth, and seventh current sources are made variable by using the amplification factor compensation signal generated by the amplification factor compensation signal generation circuit. A variable gain amplifier characterized by the above. The amplification factor compensation signal generation circuit further includes a first MOS transistor that allows a predetermined current to flow according to the amplification factor compensation signal output from the differential operational amplifier,
Each of the fourth, fifth, sixth, and seventh current sources includes second, third, fourth, and fifth MOS transistors,
2. The variable amplification factor amplifier according to claim 1, wherein the first, second, third, and fourth MOS transistors form a predetermined current mirror circuit. A sixth MOS transistor forming a predetermined current mirror circuit with the fourth MOS transistor;
A seventh MOS transistor configured to cause a predetermined current to flow through the sixth MOS transistor and to form a predetermined current mirror circuit with the fifth MOS transistor;
The sixth MOS transistor has a predetermined ratio with respect to the transistor size of the fourth MOS transistor,
3. The variable amplification factor amplifier according to claim 2, wherein the seventh MOS transistor has a predetermined ratio with respect to a transistor size of the fifth MOS transistor. 4. 4. The variable amplification factor amplifier according to claim 1, wherein the Gilbert variable amplification factor amplifier is a folded Gilbert variable amplification factor amplifier. 5.

Images