JPH1065460A - Operational amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep the operating condition of a level shift circuit constant independently of power supply fluctuation or the like and to prevent an idling current from being increased by generating a bias with an output current of a constant current circuit and setting a level shift voltage for a level shift circuit with the bias voltage. SOLUTION: An output voltage N4 of a constant current circuit 5 is given to a gate of a transistor (TR) n4 being a component of a bias circuit 4. Since TRs n6, n4 of the constant current circuit 5 are configured as a current mirror, a current 12 flowing to the bias circuit 4 depends on a ratio of mutual conductance of the TRs n6, n4 and does not include power supply fluctuation or VT fluctuation. When the mutual conductance of TRs n1, n2 in the level shift circuit 2 is the same, a level shift voltage from an output voltage N1 of the differential amplifier circuit 1 to an output voltage N2 of the level shift circuit 2 is a voltage being an output voltage N3 of the bias circuit 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an operational amplifier. In particular, the present invention relates to an operational amplifier having a push-pull circuit as an output stage.

[0002]

2. Description of the Related Art FIG. 2 shows a circuit example of an operational amplifier having a push-pull circuit in an output stage. In the case of FIG. 2, the operational amplifier includes a differential amplifier circuit 1 for differentially amplifying the inputs IN1 and IN2, a level shift circuit 2 for level-shifting and outputting the output N1, an output N1 and an output after the level shift. It comprises a push-pull circuit 3 that performs a push-pull operation by inputting N2 and a bias circuit 4.

Here, the push-pull circuit 3 is formed by cascade connection of transistors P1 and n3 having opposite polarities. The output N1 is connected to the gate of the PMOS transistor P1, and the output N
2 is input to the gate of the NMOS transistor n3. The push-pull circuit 3 operates by these two inputs and outputs the corresponding outputs to two transistors P1 and n.
The signal is output to the subsequent stage from the drain terminal which is the connection midpoint of No. 3.

The NM constituting the level shift circuit 2
Transconductance g of OS transistors n1 and n2
When m is the same, the level shift voltages of the differential outputs N1 and N2 become equal to the output N3 of the bias circuit 4, as expressed by the following equation (1).

N1−N2 = N3 (1)

[0006]

However, in the operational amplifier having the above configuration, when the threshold voltage of the PMOS transistor is VTP and the threshold voltage of the NMOS transistor is VTN, the condition given by the following equation (2) is satisfied. Thus, there is a problem that the transistors P1 and n3 always operate in the ON region, and the so-called idling current flowing through the push-pull circuit 3 increases.

VDD− | VTP | −VTN <N3 (2) In addition, since equation (2) includes various factors such as power supply fluctuations, process fluctuations, and bias voltage fluctuations, control is difficult.

The present invention has been made in view of the above points, and has a stable bias state requiring less increase in power consumption due to power supply fluctuations and process fluctuations as compared with the conventional operational amplifier. It is intended to provide an operational amplifier.

[0009]

According to the present invention, there is provided a differential amplifier circuit to which two input voltages are supplied, and a level shift circuit for level-shifting and outputting the differential output voltage. An operational amplifier including a push-pull circuit for inputting a differential output voltage and a voltage level-shifted by the level shift circuit as a gate control voltage is characterized as follows.

That is, the level shift voltage in the level shift circuit is set by a bias voltage generated by the bias circuit based on a constant current generated by the constant current circuit.

In the operational amplifier according to the present invention, a bias voltage is generated by an output current of a constant current circuit that outputs a constant current without being affected by a power supply fluctuation or a VT fluctuation, and the level shift voltage of the level shift circuit is generated by the bias voltage. Is set, the operating conditions of the level shift circuit can be kept constant irrespective of power supply fluctuations. This effectively prevents the idling current from increasing.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

(A) First Embodiment Hereinafter, a first embodiment of an operational amplifier according to the present invention will be described with reference to the drawings.
An embodiment will be described.

FIG. 1 shows a circuit configuration of the operational amplifier according to the first embodiment.
It has a configuration similar to that of the operational amplifier described in the conventional example, except that it is configured by a constant current circuit 5.

The constant current circuit 5 is composed of a resistor R2 and transistors P3, P4, n6 and N7, and has a constant current value at which the current I1 is not affected by VT fluctuations and power supply fluctuations. Source has been realized.

On the other hand, the bias circuit 4 comprises a transistor n6 of the constant current circuit 5, a transistor n4 forming a current mirror, and transistors P2 and n5 having a common drain and gate.

Next, the operation of the operational amplifier having the above configuration will be described.

Also in the case of the first embodiment, the differential amplifier circuit 1
Is output to the gate of the transistor P1 of the push-pull circuit 3, and the output N2 obtained by level-shifting the output N1 by the level shift circuit 3 is input to the gate of the transistor n3 of the push-pull circuit 3. Are the same.

When one of the transistors P1 and n3 of the push-pull circuit 3 is turned on based on this input, the other is turned off, and the output is output from the common drain terminal of the two transistors P1 and n3. It has become.

Here, parts unique to the first embodiment are as follows.
The constant current circuit 5 includes a transconductance gm of the transistor P3 and a transconductance gm of the transistor P4.
Are equal, and the transconductance of the transistor n6 is gm1, and the transconductance g of the transistor n7 is gm1.
When m is gm2, the current I1 (transistor n6
(Current flowing through the circuit) is an operation caused by the circuit represented by the following equation (3).

I1 = KT / q (ln gm1 / gm2) / R2 (3) The output voltage N4 of the constant current circuit 5 is connected to the gate of the transistor n4 constituting the bias circuit 4.
Moreover, since the transistors n6 and n4 have a current mirror configuration, the current I2 flowing through the bias circuit 4 is
It is determined by the equation (3) and the ratio of the mutual conductance gm of the transistors n6 and n4, and does not include the power supply fluctuation or the VT fluctuation.

Therefore, when the current I2 is set to about 0.1 μA, the voltage difference between the source, the gate and the drain of the transistor P2 becomes VTP, and the voltage difference between the source, the gate and the drain of the transistor n5 becomes VTN. The output voltage N3 of the circuit 4 is given by the following equation (4).

VDD− | VTP | −VTN = N3 (4) Therefore, the transistor n1 in the level shift circuit 2
And the mutual conductance gm of n2 is the same, the level shift voltage from the output voltage N1 to the output voltage N2 is equal to the voltage of the output voltage N3, and becomes the equation (4) itself.

As a result, in the push-pull circuit 3, the output voltage N1 of the differential amplifier is applied to the gate of the transistor P1, and the output voltage N1 is level-shifted by the equation (4) to the gate of the other transistor n3. Voltage will be applied. Thus, when the output terminal is unloaded, the gate voltage of both the transistors P1 and n3 becomes close to VT, so that the idle current is low and stable.

As described above, according to the first embodiment,
The constant current generated by the constant current circuit 5 is turned back to the bias circuit, and a stable bias voltage is applied to the push-pull circuit 3 irrespective of power supply fluctuation, so that the gate voltage of the PMOS transistor P1 of the push-pull circuit 3 And the gate voltage difference between the NMOS transistor n3 and
The voltage can be fixed to the voltage given by the equation (4), and the transistor P1 and the transistor n3 can operate alternately in the ON region.

As a result, it is possible to realize an operational amplifier circuit with low current consumption and a stable bias state irrespective of power supply voltage fluctuations and process fluctuations.

(B) Second Embodiment The second embodiment operates at a lower voltage than the first embodiment in which the bias state is stabilized with low current consumption against power supply voltage fluctuations and process fluctuations. A second embodiment capable of performing the following will be described.

The difference between the operational amplifier according to the second embodiment and the operational amplifier according to the first embodiment is that the transistor n of the bias circuit 2 in the circuit configuration shown in FIG.
The point is that the NMOS transistors constituting 1 and n2 are depletion type transistors.

The advantage of using a depletion-type transistor for the bias circuit 2 will be described below.

In the circuit configuration shown in FIG. 1, the power supply voltage VDD
Becomes low, the voltage of the output voltage N3 becomes close to the GND voltage according to the equation (4). For example, if the power supply voltage VDD is
1.5V, the voltage difference VTN between the source, gate and drain of the transistor n5 is 0.7V, and the voltage difference VTP between the source, gate and drain of the transistor P2 is -0.7V.
From the equation (4), the output voltage N3 = 0.1 V (= 1.5 V)
− | −0.7 | −0.7).

In this case, in the operational amplifier according to the first embodiment, the transistor n2 of the level shift circuit 2 does not operate in the ON region, and the level shift circuit 3 does not operate.

However, in the case of the second embodiment, since the transistors n1 and n2 are depletion type transistors, even if the output voltage N3 becomes close to the GND voltage by lowering the power supply voltage VDD, An ON operation can be performed, and the level shift circuit 2 can be operated as usual.

As a result, the operation of the push-pull circuit 3 can be guaranteed, and an operational amplifier that can operate at lower voltages can be realized. Note that in the case of the second embodiment, the power supply voltage VDD is VTN + | VTP |
Operable up to.

(C) Other Embodiments In the above embodiment, the explanation has been given by limiting to the operational amplifier having the push-pull output stage, but the present invention is not limited to this, and the circuit having the push-pull output stage Widely applicable. Further, the present invention can be widely applied to various electronic circuits including an operational amplifier having an output stage having such a configuration as an internal circuit. In particular, the present invention is suitably applied to an electronic component constituting a portable electronic device having a low power supply voltage and a power supply voltage supply source being a battery.

[0034]

As described above, according to the present invention, the level shift voltage of the level shift circuit that shifts the level of the differential output voltage of the differential amplifier circuit and outputs the same, and the constant current that the constant current circuit outputs is constant. By setting the bias voltage of the bias circuit generated based on the bias voltage, the level shift voltage of the level shift circuit can be stabilized regardless of power supply fluctuation. As a result, an increase in the idling current of the push-pull circuit that operates by inputting the output voltage of the differential amplifier circuit and the voltage shifted by the level shift circuit as the gate control voltage can be effectively prevented. As a result, an operational amplifier with low power consumption can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a circuit configuration of an operational amplifier according to an embodiment.

FIG. 2 is a circuit diagram showing a circuit configuration of a conventional operational amplifier.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Differential amplifier circuit, 2 ... Level shift circuit, 3 ... Push-pull circuit, 4 ... Bias circuit, 5 ... Constant current circuit.

Claims (2)

[Claims] 1. A differential amplifying circuit to which two input voltages are supplied, a level shift circuit for level-shifting and outputting the differential output voltage, and a level-shifted circuit by the differential output voltage and the level shift circuit And a push-pull circuit for inputting the voltage as a gate control voltage, the bias voltage generated by the bias circuit based on the constant current generated by the constant current circuit. An operational amplifier characterized by being set by voltage. 2. The transistor of the level shift circuit,
2. The operational amplifier according to claim 1, comprising a depletion type field effect transistor.