JPH08330868A - Variable gain circuit - Google Patents

Abstract

PURPOSE: To provide a variable gain circuit whereby a sufficient frequency band is obtained even when high gain is set. CONSTITUTION: The variable gain circuit is provided with an operational amplifier circuit 10, an internal phase compensating circuit 20, a phase compensation adjusting circuit 30 connected to the internal phase compensating circuit 20 in parallel, a gain setting circuit connected between the inverting input terminal 2 and the output terminal 3 of the operational amplifier circuit 10 and a gain setting control means 50 controlling the synchronization of the gain setting circuit 40 with the phase compensation adjusting circuit 30. The phase compensation adjusting circuit 30 is linked with high gain when the gain setting control means 50 set high gain so as to executes an operation for reducing phase compensation. When low gain is set, it is linked with low gain so as to executes the operation for enlarging phase compensation and executes the operation for obtaining the sufficient frequency and while holding the stable operation from low gain to the high one.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable gain circuit capable of widening a frequency band.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing a configuration of a conventional variable gain circuit using an operational amplifier circuit. FIG. 5 is a circuit diagram specifically showing the configuration of a conventional variable gain circuit.

A conventional variable gain circuit is an operational amplifier circuit 10.
a, a gain setting circuit 40a, and the like.

In the operational amplifier circuit 10a, MOSFETs 11a and 12a whose sources are commonly connected to the drain of the MOSFET 15a which is a constant current source form a differential input pair, and the MOSFETs 13a and 14a form an active load of the differential input pair. To do. The gate of the MOSFET 16a is MOSF
Connected to the common drain connection point of ET12a, 14a,
The source is connected to the ground terminal 101a, and the drain is the drain of the MOSFET 17a, which is a constant current source, and the output terminal 3.
connected to a.

Here, 1a is a non-inverting input terminal, 2a is an inverting input terminal, 61a is a constant current setting bias terminal, and 22 is a constant current setting bias terminal.
Reference numeral a is a phase compensation capacitance, and reference numeral 21a is a zero point adjusting MOSFET having a gate connected to the power supply terminal 100a. The operational amplifier circuit 10a forms a two-stage CMOS operational amplifier as a whole.

Further, in the gain setting circuit 40a, 45a ...
Reference numeral 49a is a gain setting resistor, 41a to 44a are resistance connection switching switch means, and 50a is a resistance switching switch control means.

In the conventional variable gain circuit having such a structure, the gain of the operational amplifier circuit 10a is controlled by switching the resistance connection switching switches 41a to 44a by the resistance switching switch control means 50a.

[0008]

However, in the above-mentioned conventional variable gain circuit, the phase compensating capacitors 22a and MO are provided.
Since the phase compensation circuit including the SFET 21a is set so that stable operation is obtained when the gain of the variable gain circuit is 1, a sufficient frequency band is obtained when the gain of the variable gain circuit is set to high gain. There was a problem that I could not.

An object of the present invention is to provide a variable gain circuit which can obtain a sufficient frequency band even when it is set to a high gain.

[0010]

To achieve the above object, a variable gain circuit according to claim 1 of the present invention comprises an operational amplifier circuit for performing operational amplification of a signal input through an input terminal, A variable variable amplifier including a gain setting circuit connected between the inverting input terminal and the output terminal of the operational amplifier circuit, for setting the gain of the operational amplifier, and a phase compensation circuit for compensating the phase of the signal subjected to the operational amplifier. In a gain circuit, a phase compensation adjustment circuit that is connected in parallel with the phase compensation circuit and adjusts the phase compensation according to the set gain, and a gain setting that synchronizes the adjustment of the phase compensation and the gain setting. And control means.

[0011]

In the variable gain circuit according to claim 1 of the present invention, the operational amplifier circuit performs operational amplification of a signal input through the input terminal, and the signal is provided between the inverting input terminal and the output terminal of the operational amplifier circuit. When the gain of the operational amplification is set by the connected gain setting circuit and the phase compensation circuit performs the phase compensation of the signal for which the operational amplification is performed, the phase compensation adjustment circuit connected in parallel with the phase compensation circuit The phase compensation is adjusted according to the set gain, and the gain setting control means synchronizes the adjustment of the phase compensation with the setting of the gain.

[0012]

1 is a block diagram showing the configuration of a variable gain circuit according to an embodiment. In the figure, 10 is an operational amplifier circuit, 2
Reference numeral 0 is an internal phase compensation circuit, 30 is a phase compensation adjustment circuit connected in parallel to the internal phase compensation circuit 20, and 40 is a gain setting circuit connected between the inverting input terminal 2 and the output terminal 3 of the operational amplifier circuit 10. , 50 are gain setting control means for synchronously controlling the gain setting circuit 40 and the phase compensation adjusting circuit 30.

In the above configuration, the phase compensation adjustment circuit 30
Operates when the gain setting control means 50 is set to a high gain so as to reduce the phase compensation in conjunction with it.
When the gain is set to a low gain, the phase compensation works in conjunction with it to operate so that a sufficient frequency band can be obtained while maintaining stable operation from low gain to high gain.

FIG. 2 is a circuit diagram specifically showing the configuration of the variable gain circuit. The operational amplifier circuit 10 has a constant current source P
P-channel MOSFET having a common source connected to the power supply terminal 100 via the channel MOSFET 15.
A differential input pair consisting of 11, 12 and a P-channel MOSF
N-channel MOSF in which the drain and gate are connected to the drain of ET11 and the source is connected to the ground terminal 101
ET13 and the gate are commonly connected to the gate of the N-channel MOSFET 13, and the drain is a P-channel MOSF
An N-channel MOSFET 14 which is commonly connected to the drain of the ET 12 and whose source is connected to the ground terminal 101;
The gate is connected to the common drain connection point of the P-channel MOSFET 12 and the N-channel MOSFET 14, the drain is connected to the power supply terminal 100 via the P-channel MOSFET 17 which is a constant current source, and the source is the ground terminal 1.
And an N-channel MOSFET 16 connected to 01.

In the internal phase compensation circuit 20, the sources have P-channel MOSFET 12 and N-channel MOSFET 1.
An N-channel MOSFET 21 connected to the drain common connection point of No. 4, a gate connected to the power supply terminal 100, and a drain connected to one terminal of the phase compensation capacitance 22;
The other terminal not connected to the channel MOSFET 21 is composed of a phase compensation capacitor 22 connected to the drain of the N-channel MOSFET 16.

The phase compensation adjustment circuit 30 has one terminal of N terminal.
The phase compensation adjustment capacitors 35, 36, 37, 38 connected to the drain of the channel MOSFET 16 and the other terminal not connected to the drain of the N-channel MOSFET 16 are connected to the drain, and the sources are commonly connected to the N-channel MO.
An N-channel MOSFET 31, which is connected to the gate of the SFET 16 and whose gate is connected to the gain setting control means 50,
32, 33, 34.

The gain setting circuit 40 includes a feedback resistor 45 connected between the inverting input terminal 2 and the output terminal 3 of the operational amplifier circuit 10 and a switch means 41 whose opening and closing is controlled by the gain setting control means 50. 42, 43, 44, and gain setting resistors 41, 42, 43, which are connected to the inverting input terminal 2 by the switch means 41, 42, 43, 44 and whose other end is commonly connected to the reference power supply terminal 62. And 44.

A gain setting circuit 40 having the above-mentioned specific configuration.
The operation of will be described. The set gains are switched by the gain setting control means 50.
When all 4 are OFF, the lowest value is 1, and when all are ON, the highest gain is obtained.

N-channel MOS of the phase compensation adjustment circuit 30
The FETs 31 to 34 are switches controlled by the gain setting control means 50, and are turned OFF / ON in conjunction with ON / OFF of the switch means 41 to 44 in the gain setting circuit 40.

That is, all the switch means 41 to 44 are turned on.
N channel MOSFE when the maximum gain is set by
T31 to 34 are turned off, and the phase compensation adjustment circuit 30 is separated from the operational amplifier circuit 10. On the other hand, when the switch means 41 to 44 are all OFF and the minimum gain, the N-channel MOSFETs 31 to 34 are turned ON and the phase compensation adjustment circuit 30 is connected to the operational amplifier circuit 10.

Therefore, the internal phase compensation circuit 20 only needs to perform compensation in the case of the highest gain, and the phase compensation capacitance 22 can be made small, so that a wide frequency band can be taken. Further, if the phase compensation capacitors 35 to 38 forming the phase compensation adjustment circuit 30 are weighted corresponding to the weighting of the gain setting resistors 46 to 49, a sufficiently wide frequency band can be obtained at each set gain. . [Modification] FIG. 3 is a circuit diagram specifically showing the configuration of a variable gain circuit of a modification. The variable gain circuit of the modified example includes an N-channel MOSFET 21 that constitutes the internal phase compensation circuit 20.
And an N-channel MO that constitutes the phase compensation adjustment circuit 30.
It is configured by replacing the SFETs 31 to 34 with P-channel MOSFETs. Even if such replacement is performed, the polarity is changed and no essential difference occurs.

[0022]

According to the variable gain circuit of the first aspect of the present invention, the operational amplifier circuit performs operational amplification of the signal input through the input terminal, and the inverting input terminal and the output terminal of the operational amplifier circuit. And a phase connected in parallel with the phase compensation circuit when the gain of the operational amplification is set by the gain setting circuit connected between the phase compensation circuit and the phase compensation circuit for phase compensation of the signal for which the operational amplification is performed. The compensation adjustment circuit adjusts the phase compensation according to the set gain, and the gain setting control means synchronizes the adjustment of the phase compensation with the setting of the gain. Therefore, even when the high gain is set, a wide frequency range is set. Bandwidth can be secured.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a variable gain circuit of an embodiment.

FIG. 2 is a circuit diagram specifically showing a configuration of a variable gain circuit.

FIG. 3 is a circuit diagram specifically showing a configuration of a variable gain circuit of a modified example.

FIG. 4 is a block diagram showing a configuration of a conventional variable gain circuit using an operational amplifier circuit.

FIG. 5 is a circuit diagram specifically showing a configuration of a conventional variable gain circuit.

[Explanation of symbols]

 10 operational amplifier circuit 20 internal phase compensation circuit 30 phase compensation adjustment circuit 40 gain setting circuit 50 gain setting control means

Claims (1)

[Claims] 1. An operational amplifier circuit for performing operational amplification of a signal input through an input terminal, and an operational amplifier circuit connected between an inverting input terminal and an output terminal of the operational amplifier circuit for setting the gain of the operational amplifier. A variable gain circuit comprising a gain setting circuit and a phase compensating circuit for compensating the phase of a signal for which the operational amplification is performed, the variable gain circuit being connected in parallel with the phase compensating circuit, the phase compensating circuit according to the set gain. And a gain setting control means for synchronizing the adjustment of the phase compensation and the setting of the gain.