JPH0795662B2 - Operational amplifier and driving method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operational amplifier used in a system requiring high precision and high bandwidth.

[0002]

2. Description of the Related Art As a differential amplification stage in an operational amplifier which has a single amplification stage and realizes high gain and high bandwidth,
A folded cascode circuit, which has a wide output voltage span, has been conventionally used. For example,
The paper "10-bit 50Msps pipeline type CMOSA" by Yoyanagi et al., Which was described in P9 to P15 of the technical digest of the 1992 IEICE Spring Conference.
A folded cascode circuit is used in the amplification stage of the general-purpose operational amplifier described in "/ D converter." A conventional operational amplifier in which a differential amplification stage is configured by this folded cascode circuit is shown in the circuit diagram of FIG. In this figure, the folded cascode circuit is the shaded area, which is characterized in that it reduces the Miller capacitance generated in the amplifier stage and allows a wide output span.

On the other hand, a constant current circuit that enables high output impedance is disclosed in Edward Sackinger (Eduard Sa) described in Journal of Solid State Circuits P289-P298 in February 1990.
CKinger) et al. “A High-Swing,
High-Impedance MOS Cas-co
de Circuit ”. This constant current circuit is composed of a regulated cascode circuit (RGC). The regulated cascode circuit requires more elements than the folded cascode circuit, but is characterized by having a larger output impedance. As described above, the regulated cascode circuit has been publicly known, but has conventionally been used as a constant current circuit.

[0004]

In the conventional operational amplifier using the folded cascode circuit in the differential amplification stage,
Even if the Wilson current mirror circuit is used as the active load, if the band is selected to be several hundred MHz, it will be about 60d.
I could get only B gain. Further, in the conventional operational amplifier, sufficient gain cannot be obtained when driven at a low voltage of 5 V or less. Therefore, an object of the present invention is to provide an operational amplifier having a high gain and to provide an operational amplifier that can be driven at a low voltage of 5 V or less.

[0005]

In order to solve the above problems, the present invention provides the following means. The operational amplifier of the present invention comprises one differential amplification stage,
In an operational amplifier having one differential amplification stage, the differential amplification stage includes a differential input circuit, a first and a second regulated cascode circuit, and a current mirror circuit such as a Wilson current mirror circuit. The differential input circuit has first and second inputs and first and second outputs. The first regulated cascode circuit has a source connected to a power supply line and a gate voltage-driven transistor MP1. And the transistor MP1
MP5 with source connected to drain
And a transistor MP having a gate and a source connected to the drain and the source of the transistor MP1, respectively.
The second regulated cascode circuit includes a transistor MP2 whose source is connected to a power supply line and whose gate is voltage-driven, and said transistor MP2.
Transistor MP6 with source connected to drain of 2
And a transistor MP whose gate and source are connected to the drain and source of the transistor MP2, respectively.
4, the drain of the transistor MP3 and the gate of the transistor MP5 are short-circuited and supplied with a constant current, and the drain of the transistor MP4 and the gate of the transistor MP6 are short-circuited and supplied with a constant current. The inputs of the first and second regulated cascode circuits are the first of the differential input circuits.
And a second output to the gate of the transistor MP3 and the gate of the transistor MP4, respectively, as a current change, the current mirror circuit has first and second inputs and one output, and the first and second outputs are provided. The output of the regulated cascode circuit of No. 2 is given as a current change from the drain of the transistor MP5 and the drain of the transistor MP6 to the first and second inputs of the current mirror circuit, respectively. In a method of driving an operational amplifier having one differential amplification stage, the differential amplification stage is composed of a differential input circuit, and first and second regulated cascode circuits and a current mirror circuit such as a Wilson current mirror circuit. And the differential input circuit includes first and second inputs and a first input.
And a second output, the first regulated cascode circuit includes a transistor MP1 having a source connected to a power supply line and a gate having a voltage driven, and a transistor MP5 having a source connected to a drain of the transistor MP1. And a transistor MP3 having a gate and a source connected to the drain and the source of the transistor MP1, respectively. In the second regulated cascode circuit, the source is connected to a power supply line and the gate is driven by a voltage MP2. , A transistor MP6 having a source connected to the drain of the transistor MP2 and a transistor MP4 having a gate and a source connected to the drain and source of the transistor MP2, respectively. The gate of the static MP5, are short-circuited, are supplied with constant current, said transistor MP4
And the gate of the transistor MP6 are short-circuited and supplied with a constant current, and the inputs of the first and second regulated cascode circuits are the first and second outputs of the differential input circuit. From the transistor MP
The current mirror circuit has first and second inputs and one output, and the outputs of the first and second regulated cascode circuits are provided to the gate of the transistor MP4 and the gate of the transistor MP4, respectively. Is a driving method of the operational amplifier which is given as a current change from the drain of the transistor MP5 and the drain of the transistor MP6 to the first and second inputs of the current mirror circuit, respectively. A method for driving an operational amplifier characterized by driving.

[0006]

According to the structure of the present invention in which the regulated cascode circuit is used in the differential amplification stage, the output impedance of the differential amplification stage can be increased. Further, by driving the operational amplifier at a low voltage, the output impedance can be more effectively increased as compared with the conventional circuit configuration.

[0007]

FIG. 1 is a circuit diagram of an embodiment of the present invention. This
In one embodiment, there is one differential amplification stage and two
It is composed of a circuitized cascode circuit. In Figure 1
The area surrounded by diagonal lines is regulated cascode
The circuit 1 has a differential structure. Two rules
Differential amplifier stage with a rated cascode circuit is
It constitutes the amplification part of the ruend. These two regulations
Corresponding elements in a rated cascode circuit
Have equal electrical properties. 2 is Wilson Carre
It is a non-mirror circuit and regulated cascode times
It is used as an active road. In this example
The input stage is an n-channel transistor MN1 and
It is composed of MN2. Also, for parts other than the constant current source
The transistor of the regulated cascode circuit is p
It is a channel. The regulated cascode is shown in Fig. 3 (a).
FIG. 2B shows an equivalent circuit. In the figure
R and g shown in_mIs the output impedance of the transistor
And transconductance, respectively. Figure
Transistor T shown inside₁, T₂, T₃, T_FourWith
The output impedance of the transistor with the same subscript
Dance r to r₀₁, R₀₂, R₀₃, R₀₄Respectively,
Output impedance R of the operational amplifier of FIG. _rCalculate
And R_r≒ r₀₂r₀₃r₀₄g_m2g_m4 It can be expressed as (1). In addition, as shown in FIG.
The equivalent circuit of the folded cascode circuit shown in FIG.
Output impedance R_fIs calculated as R_f≒ r₀₂r₀₄g_m4 It can be expressed as (2). Output impedance of each transistor
Dance r and mutual conductance g_mAre equal
From the equations (1) and (2), the regulated cascode times
Output impedance by using a path_mDouble
It can be large. The gain of the amplifier is the input stage
Transistor transconductance and amplifier output output
Since it is given by the product of the pedestal, as shown in Fig. 1.
By using a regulated cascode circuit
The overall gain can be increased.

Although the input stage transistor is an n-channel in the embodiment shown in FIG. 1, it may be an npn transistor. Although the transistor of the regulated cascode circuit is a p-channel transistor, it may be a pnp transistor. Further, the input stage transistor may be a p-channel or pnp, and the transistor of the regulated cascode circuit may be an n-channel or npn. However, there is no particular limitation on the transistor of the constant current source in the regulated cascode circuit.

Next, a case where the operational amplifier of FIG. 1 is driven at a low voltage will be described. Generally, when the operational amplifier is driven at a low voltage, the reference voltage of the power supply unit (not shown) is lowered and the current I flowing through each branch is reduced.

On the other hand, as shown by the equations (1) and (2), the output impedance of the regulated cascode circuit becomes rg _m times larger than the output impedance of the folded cascode circuit. Here, since the output impedance r and the transconductance g _m of the transistor are respectively 1 / I and √I with respect to the drain current I, when the power supply voltage is lowered and the current I is reduced, the regulated cascode circuit and the fall cascode circuit are generated. The output impedance ratio of the dead cascode circuit opens at a ratio of 1 / √I,
The output impedance increases. As mentioned above, the gain of the amplifier is given by the product of the transconductance of the input stage transistor and the output impedance of the amplification stage.
With this driving method, the gain can be dramatically increased as compared with the case where the conventional folded cascode circuit is used. By driving the operational amplifier of FIG. 1 at 3 to 5 V, the output impedance could be increased more than when driven at a voltage of 5 V or higher.

[0011]

As described above, in the differential amplifier of the present invention, a high output impedance can be obtained, so that a high gain of 80 dB or more can be easily realized even in the frequency band of several hundred MHz. The effect is that you can do it. Further, there is an effect that the above effect is increased by driving the operational amplifier of the present invention at a low voltage of 3 to 5V.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

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

FIG. 3 is a circuit diagram and an equivalent circuit diagram of a regulated cascode circuit.

FIG. 4 is a circuit diagram and an equivalent circuit diagram of a folded cascode circuit.

[Explanation of symbols]

 1 regulated cascode circuit 2 Wilson current mirror circuit 3 folded cascode circuit

Claims (6)

[Claims] 1. An operational amplifier having one differential amplification stage, wherein the differential amplification stage is a differential input circuit, and current mirror circuits such as first and second regulated cascode circuits and a Wilson current mirror circuit. The differential input circuit has first and second inputs and first and second outputs, and the first regulated cascode circuit has a source connected to a power supply line and a gate connected to a voltage. The second regulated cascode includes a driven transistor MP1, a transistor MP5 having a source connected to the drain of the transistor MP1, and a transistor MP3 having a gate and a source connected to the drain and the source of the transistor MP1, respectively. The circuit has a source connected to the power supply line and a gate driven by voltage. Transistor MP2, a transistor MP6 whose source is connected to the drain of the transistor MP2, and a transistor MP4 whose gate and source are connected to the drain and source of the transistor MP2, respectively. The drain of the transistor MP3 and the transistor MP4 The gate of MP5 is short-circuited and supplied with a constant current, the drain of the transistor MP4 and the gate of the transistor MP6 are short-circuited and supplied with a constant current, and the first and second regulators are connected. The input of the Ted cascode circuit is the gate of the transistor MP3 and the transistor M from the first and second outputs of the differential input circuit.
The current mirror circuit is supplied to the gate of P4 as a current change, and the current mirror circuit has first and second inputs and 1
Two outputs, the outputs of the first and second regulated cascode circuits change currents from the drains of the transistors MP5 and MP6 to the first and second inputs of the current mirror circuit, respectively. An operational amplifier characterized by being provided as. 2. The operational amplifier according to claim 1, wherein the differential amplification stage includes a single-ended amplification section having two regulated cascode circuits. 3. The operational amplifier according to claim 2, wherein elements corresponding to each other in the two regulated cascode circuits have the same electric characteristics. 4. The input stage is constituted by an n-channel or npn transistor, and the transistors other than the constant current source constituting the regulated cascode circuit are constituted by p-channel or pnp transistors. Operational amplifier. 5. The input stage is composed of a p-channel or pnp transistor, and the transistors other than the constant current source forming the regulated cascode circuit are n-channel or n-channel.
The operational amplifier according to claim 1, wherein the operational amplifier is formed of a pn transistor. 6. An operational amplifier having one differential amplification stage, wherein the differential amplification stage is a differential input circuit, and current mirror circuits such as first and second regulated cascode circuits and a Wilson current mirror circuit. The differential input circuit has first and second inputs and first and second outputs, and the first regulated cascode circuit has a source connected to a power supply line and a gate connected to a voltage. The second regulated cascode includes a driven transistor MP1, a transistor MP5 having a source connected to the drain of the transistor MP1, and a transistor MP3 having a gate and a source connected to the drain and the source of the transistor MP1, respectively. The circuit has a source connected to the power supply line and a gate driven by voltage. Transistor MP2, a transistor MP6 whose source is connected to the drain of the transistor MP2, and a transistor MP4 whose gate and source are connected to the drain and source of the transistor MP2, respectively. The drain of the transistor MP3 and the transistor MP4 The gate of MP5 is short-circuited and supplied with a constant current, the drain of the transistor MP4 and the gate of the transistor MP6 are short-circuited and supplied with a constant current, and the first and second regulators are connected. The input of the Ted cascode circuit is the gate of the transistor MP3 and the transistor M from the first and second outputs of the differential input circuit.
The current mirror circuit is supplied to the gate of P4 as a current change, and the current mirror circuit has first and second inputs and 1
Two outputs, the outputs of the first and second regulated cascode circuits change currents from the drains of the transistors MP5 and MP6 to the first and second inputs of the current mirror circuit, respectively. The method for driving an operational amplifier according to claim 1, characterized in that the operational amplifier is driven by a power supply voltage of 5 V or less and 3 V or more.