JPH03195109A - Differential amplifier circuit - Google Patents

Abstract

PURPOSE:To select a phase compensating capacity value corresponding to gain by parallelly connecting plural phase compensating capacitors, providing switches between the respective capacitors and connecting points of the respective capacitors and switching the phase compensating capacity value as well corresponding to gain switching. CONSTITUTION:A second phase compensating capacitor C2 is connected to one terminal of a phase compensating capacitor C1 and between the other terminal of this second phase compensating capacitor C2 and the other terminal of the phase compensating capacitor C1, a switch S3 is connected by an MOS transistor. The gate of this MOS transistor is connected to the output of an inverter I1 and the gate of the switch S1. Therefore, the phase compensating capacity value can be switched as well corresponding to gain switching. Thus, phase compensation is enabled corresponding to respective gains and regardless of the gain, a satisfactory characteristic can be obtained. Then, the width of the gain can be widely obtained so as to be switched by the selection of the gain compensating capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a differential amplifier circuit whose gain can be changed according to the input signal level.

[Prior Art] FIG. 2 is a basic circuit diagram of a conventional gain-switchable differential amplifier circuit. In the figure, (1) is a differential amplifier, R1,
R2 and R3 are resistors, 81.82 is a MOS transistor switch, and II is an inverter.

A resistor R is connected between the output V out of the differential amplifier (1) and the ground.
IR2 and R3 are connected in series, and a switch S1 is connected between the negative phase input Vin (→ and the connection point of the resistors R1 and R2) of the differential amplifier (1), and the switch S1 is connected between the negative phase input Via (→ and the resistor R
A switch S2 is connected between the connection point of 2 and R3,
The gate input of the -08) transistor constituting these switches is connected to the switch 81 for the gain switching input vHLK.
is connected to via an inverter II, and directly connected to a switch S2, and a phase compensation capacitor CI is connected to an appropriate position of the differential amplifier (1).

Next, the operation will be explained. Gain switching power VHL is H
In this case, the switch s1 is turned off and the switch S2 is turned on, so the gain in this differential amplifier circuit is.

Vout = fr(Vir+(+)-Win(-)
) (K: gain of amplifier) When the gain switching input VHL is L, the following is similarly obtained. Therefore, when the gain switching input VHL is H, the gain is A, which is a high gain of 9, and when VHL is L, the gain is A.
When L is set to low gain, gain switching becomes possible.

However, the value of the phase compensation capacitor c1 was the same regardless of the gain.

[Problem to be solved by the invention] Since the conventional gain-switchable differential amplifier was configured as described above, the phase compensation capacitance value remains constant even when the gain changes, so phase compensation at low gain is not possible. If the capacitance value is set large for this reason, the frequency characteristics (especially slew rate) will be poor at high gain.On the other hand, if the capacitance value is set small for phase compensation at high gain, there will be no phase margin at low gain, resulting in oscillation. In many cases, it becomes necessary to select a capacitance value that can be used for both gains, and in this case, there are problems such as a characteristic in which Kana cutting performance is suppressed for both gains.

Furthermore, as the gain difference increases, the above-mentioned problem increases, so there is a problem that the gain selection range becomes narrower. If you want to obtain an output with a large change in rounding or gain, you will need two types of differential amplifier circuits, one high gain and one low gain, resulting in an increase in scale. The purpose of this invention is to obtain a differential amplifier circuit that can also switch the value of one-phase compensation capacitance according to the switching of the gain. Such a differential amplifier circuit is a gain-switchable differential amplifier circuit in which a plurality of phase compensation capacitors are connected in parallel, and a switch is provided between each capacitor and a connection point between the capacitors.

[Action J In the differential amplifier circuit of the present invention, the phase compensation capacitance value is also switched in accordance with the gain switching, and the phase compensation capacitance value can be selected according to the gain, so excellent characteristics can be obtained for each gain. example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of a differential amplifier circuit which is an embodiment of the present invention. First, in comparison with the conventional diagram shown in FIG. 2, a second phase compensation capacitor C2 is connected to one terminal of the first phase compensation capacitor CI.
between the other terminal of this second phase compensation capacitor C2 and the other terminal of the phase compensation capacitor CI, connect VC108) transistor r7+83, and connect this MOS)
The gate of the inverter is connected to the output of the inverter 11 and the gate of the switch 81.

Next Kl! If'F will be explained. When gain switching input V) IL is ■, switch s1 is off, switch S
2 is on, the gain AH of this differential amplifier circuit is based on equation (1). At this time, since the switch S3 is off, the phase compensation capacitor is only C1.

Next K, gain switching input Vl (if L is L, switch S
Since l is on and switch S2 is off, the gain AL of this differential amplifier circuit is from equation (2).Furthermore, at this time, since switch s3 is on, the phase compensation capacitor (i, Since cl and 02 are connected in parallel, the combined capacitance C is C=CI +C2...(3) Therefore, at high gain, the phase compensation capacitance can be kept small by using only CI.Ninth, the frequency characteristics (especially When the gain is low, the phase compensation capacitor becomes a combined capacitance of C1 and 02 and becomes large, so a large phase margin can be obtained, and good characteristics can be obtained without oscillation.

In the above embodiment, the case where the gain switching and the phase compensation capacitance switching are performed in two stages is shown, but this can be similarly configured even in the case of several stages.

[Effects of the Invention] As described above, according to the present invention, the phase compensation capacitance value can also be switched in accordance with gain switching, so phase compensation can be performed in accordance with each gain, and excellent performance can be achieved regardless of the gain. It has the effect of obtaining characteristics.

Furthermore, by selecting the phase compensation capacitor, it is possible to increase the width (size) of the gain that can be switched. Since there is no need to use a two-bridge type differential layer and only one differential amplifier is required, the circuit can be made smaller.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a gain switchable differential amplifier circuit according to an embodiment of the present invention, and FIG. 2 is a basic circuit diagram of a conventional gain switchable differential amplifier circuit. In the figure, (1) is a differential amplifier, R1 to R3 are first to third resistors, 81 to S3 are fsl to third VO8) transistor switches CI, and C2 is first to third resistors. The second phase compensation capacitor, II, represents an inverter. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A first, a second, and a third resistor are connected in series between the output terminal of the differential amplifier and the ground, and a first resistor is connected between the connection point of the first and second resistors and the negative phase input of the differential amplifier. , a second MOSFET is connected between the connection point of the second and third resistors and the negative phase input, and the second MOSFET is connected between the first and second M
The gates of the OSFETs are respectively connected to the output and input of an inverter, the input of the inverter is used as a gain switching input terminal, and a first phase compensation capacitor is connected to the differential amplifier,
One terminal of a second phase compensation capacitor is connected to one terminal of the first phase compensation capacitor, and a third MOSFET is connected between the other terminal and the other terminal of the first phase compensation capacitor. A differential amplifier circuit characterized in that the gate of the MOSFET is connected to the output of the inverter.