JP3376259B2 - Differential amplifier - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential amplifier, and more particularly to a differential amplifier with good settling characteristics and low power consumption.

[0002]

2. Description of the Related Art The circuit configuration of a conventional differential amplifier is shown in FIG. This differential amplifier is described in "Analog Integrated Circuit Design Technology for VLSI, Vol.
G. Mayer, Publisher Baifukan p. 317)).

The circuit of the differential amplifier shown in FIG. 3 will be described below. N-type MO connected to bias voltage 104
The constant current source transistor 204 of S is connected to the common source of the pair of input n-type transistors 200 and 202, and operates so that the sum current flowing through the input transistors 200 and 202 becomes constant.

The voltage input to the input terminals 100 and 102 is converted into a current by the input transistors 200 and 202, and the differential voltage component is the active load p-type transistors 206 and 20.
8 is amplified and converted into a voltage, and the output voltage of the drain of the input transistor 202 is applied to the gate electrode of the output p-type transistor 210.
It is amplified by 0 and output to the output terminal 106.

In order to stabilize the operation of the differential amplifier, the phase compensation capacitor 300 is connected between the gate of the output transistor 210 and the output terminal 106.

Further, in order to drive the load resistance attached to the output terminal 106, the drain of the output constant current source n-type MOS transistor 212 is connected to the output terminal 106, and the gate of the output constant current source transistor 212 has a bias voltage 104. Connected to.

The maximum value of the settling time of this differential amplifier is the maximum value of the current flowing in the input transistor 202 and the active load transistor 206, that is, the current value i which constantly flows in the current source transistor 204, Value t divided by the capacitance C of 300 and the fluctuation voltage V of the output
= I / CV sec.

On the other hand, among the characteristics of the differential amplifier, as for the slew rate, the rise time of the output voltage when an ideal pulse with a fast rise is applied to the input is observed with an oscilloscope, and the change in the output voltage is V / μs. Expressed as Use a sine wave instead of a pulse to raise the frequency little by little,
It can also be obtained from the maximum frequency at which the output waveform does not cause distortion and the amplitude at that time. High slew rate OP amplifier is several 100V / μs, special one is several kV / μs
There is also one. This gives a measure of how large the amplitude voltage of the output of the OP amplifier can be at high frequencies.

Therefore, the settling time of the differential amplifier is shortened as the dynamic range and the high frequency characteristics of the input stage are higher at the rising edge of the input pulse, which is the same as the slew rate, but the capacitance for phase compensation of the output stage is increased. Therefore, it is used in the expression that the output waveform is rounded and the settling time characteristic as a differential amplifier is deteriorated.

[0010]

In such a differential amplifier, it is necessary to increase the bias current of the input transistor pair in order to increase the settling speed.

Conventionally, as described above, since the bias current is supplied by the constant current source, the current consumption must be constantly increased in order to secure a large current required only during settling. There was a point.

An object of the present invention is to speed up settling of a differential amplifier with low power consumption.

[0013]

SUMMARY OF THE INVENTION The present invention achieves the above-mentioned object, and provides a differential input stage that operates at a constant current and a differential input stage.
Differential amplification output stage that receives and outputs the output of the dynamic input stage,
Stable coupling circuit between the differential input stage and the differential amplification output stage
Differential consisting of a phase compensation circuit that compensates
In the amplifier, a difference occurs in the input voltage of the differential input stage.
Of the differential detection stage and the current output of the differential detection stage
A current / voltage converter for converting force into a voltage output, and
The output of the voltage converter exceeds the threshold voltage.
And a current feedback section for supplying supplemental current to the differential input stage.
The differential input stage includes a MOS transistor pair and the MO transistor pair.
Constant current source MO connected to common source of S transistor pair
S transistor and each drain of the MOS transistor pair
In-connected current mirror active load transitions
And a differential amplifier output stage
Output MO with gate connected to one of load transistor pair
S transistor and load of the output MOS transistor
And a constant current source MOS transistor
The phase compensation circuit is connected to one of the active load transistor pair and the front side.
It is connected between the output of the output MOS transistor and
The differential detection stage uses the output of the differential input stage as one input terminal.
To the feedback differential transformer that receives the other input terminal as the reference voltage.
The current / voltage converter has a pair of transistors and the feedback differential
A gate and a gate connected to the load of the transistor pair, respectively.
It consists of a pair of conversion MOS transistors directly connected to the rain,
The current feedback section includes a drain of the conversion MOS transistor pair.
Feedback MOS transistor in which each gate is connected to IN
And a drain of the feedback MOS transistor pair.
Is connected to the current supply section of the differential input stage.
And Furthermore, in the differential amplifier described above,
A constant current source MOS transistor is used as the load of the feedback differential transistor pair.
A constant current source MOS transistor is connected to the transistor pair.
A constant bias voltage is supplied to the gates of the
The bias voltage is the load of the output MOS transistor
Is supplied to the gate of the constant current source MOS transistor
It is characterized by

The present invention also provides a differential operating with a steady current.
An input stage and a differential amplifier that receives and outputs the output of the differential input stage.
Width output stage, the differential input stage and the differential amplification output stage
Phase compensation circuit that compensates stable operation of coupling circuit
A differential amplifier consisting of
A differential detection stage for detecting a difference in voltage,
Current / voltage conversion that converts the current output of the detection stage to a voltage output
Section and the output of the current / voltage conversion section
When the voltage exceeds the voltage, it is used as the supplemental current of the differential input stage.
A current feedback section, and the differential input stage is a MOS transistor.
And a common source of the MOS transistor pair
Constant current source MOS transistor and the MOS transistor
Of the current mirror configuration connected to each drain of the star pair
And a differential amplification output.
The power stage connects the gate to one of the active load transistor pair.
The continuous output MOS transistor and the output MOS transistor
From the constant current source MOS transistor which becomes the load of the transistor
And the phase compensation circuit comprises the active load transistor.
Between one of the data pair and the output of the output MOS transistor
And the differential detection stage outputs the output of the differential input stage.
Received by one input terminal and set the other input terminal as reference voltage
The current / voltage conversion unit having a feedback differential transistor pair
Are connected to the loads of the feedback differential transistor pair, respectively.
The current feedback unit, the current feedback unit
Such as a pair of feedback MOS transistors connected between the source and the source
And the drain of the feedback MOS transistor pair is
It is characterized in that it is connected to the current supply section of the differential input stage.

Further , according to the present invention, each gate is connected to an input terminal.
And a pair of input transistors whose sources are commonly connected
Connected to the common source of the input transistor pair,
A current source transistor for supplying a bias current, and the input
The output current from the drain of the transistor pair is
IN and connect one drain to a common gate
Active load transistor pair and the active load transistor
An output amplification stage for inputting and amplifying the output voltage of
Output of active load transistor pair and output of said output amplification stage
A differential amplifier having a phase compensation capacitance connected between terminals
Where the input transistor pair has a drain
The common gate of the active load transistor pair and this active negative
First transistor connected to one drain of the load transistor pair
The input transistor and drain are the active load transistors
Second input transistor connected to the other drain of the
And a common gate of the active load transistor pair.
The third transistor that receives the gate voltage as one input and the other
When the input voltage of the input transistor pair is the same,
Voltage equal to the gate voltage of the active load transistor pair of
And a fourth transistor whose pressure is applied to the other input.
The transistor pair of the feedback circuit in which the source is commonly connected,
A bias voltage is applied to the common source of the transistor pair of the feedback circuit.
A current source transistor of a feedback circuit that supplies a current,
Output from the drain of each of the third and fourth transistors
The first and second current-electric currents that input force current and convert it into voltage
A pair of current-voltage conversion circuits having a pressure conversion circuit;
The output voltage of a pair of current-voltage conversion circuits is applied to each gate.
Connected to the common source of the pair of input transistors
Output transistor pair of the feedback circuit with drain connected
Having an output voltage of the output voltage of the current-voltage conversion circuit
When the input voltage of the input transistor pair is equal,
Is the threshold of the output transistor pair of the feedback circuit.
Bias voltage below the bias voltage of the input transistor pair
The input voltage of the first input transistor without increasing
Is larger than the second input transistor, the third
The drain current of the transistor
One current-voltage conversion circuit of the path is turned on, and the first input voltage is turned on.
The input voltage of the input transistor is the second input transistor
The drain voltage of the fourth transistor when
The other current of the feedback circuit to increase the flow - voltage conversion times
Turn on the path and turn on the bias current of the input transistor pair.
It is characterized by increasing.

A high-speed settling differential amplifier according to the present invention supplies a bias current by connecting a pair of input transistors having respective gates as input terminals and commonly connecting sources and a common source of the input transistor pairs. An output current from the drain of the current source transistor and the input transistor pair is input to each drain, and the output voltage of the active load transistor pair in which one drain is connected to a common gate and the output voltage of the active load transistor pair are input. A phase compensation capacitance connected between the output amplification stage for amplification, the output of the active load transistor pair, and the output terminal of the output amplification stage, and the gate voltage of the active load transistor pair as one input, and the other Is equal to the gate voltage of the active load transistor pair when the input voltage of the input transistor pair is equal. From a drain of the input transistor pair of the feedback circuit, a current source transistor of the feedback circuit that supplies a bias current to the common source of the input transistor pair of the feedback circuit, A pair of current-voltage conversion circuits for inputting the output current of the input voltage and converting the output current to a voltage, and the output voltages of the pair of current-voltage conversion circuits are connected to their respective gates, and a common source of the input transistor pair of the input amplification stage is connected. When the output voltage of the output voltage of the current-voltage conversion circuit is equal to the input voltage of the input transistor pair,
A differential amplifier characterized in that the threshold voltage of the output transistor of the feedback circuit is equal to or lower than the threshold voltage, and when a difference occurs between two input voltages applied to the gate of the input amplification stage, that is, the gate of the active load transistor. When the voltage deviates in a certain direction from the reference voltage applied to the input transistor of the feedback circuit, the output current of one input transistor of the feedback circuit increases, and when it deviates in the opposite direction, the voltage of the other input transistor of the feedback circuit increases. The pair of current-voltage conversion circuits of the feedback circuit, which operates so that the output current increases and inputs the output current of each input transistor of the restoration circuit, increases with the increase of the current of the input transistor of the feedback circuit.
When the output transistor of the feedback circuit operates to increase the output voltage, and the threshold voltage of one of the gate voltages of the pair of output transistors of the feedback circuit exceeds the threshold voltage, the bias current of the input amplification stage It is characterized in that it operates so as to increase.

[Operation] A feedback circuit is provided which works so as to increase the bias current of the input stage of the differential amplifier when a large differential voltage is applied to the inputs of the differential amplifier.

As a result, when a high speed settling is conventionally realized, the bias current of the input stage of the differential amplifier is constantly increased. It is possible to suppress an increase in current consumption.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 1, the preferred embodiment of the present invention comprises an input amplification stage 600, an output amplification stage 800, a phase compensation capacitor 300, a feedback circuit 500, and a feedback circuit 50.
0 is only when a differential voltage is generated in the input amplification stage 600,
It is necessary to operate to increase the current in the input amplification stage 600.

[First Embodiment] Next, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of the first embodiment of the present invention.

The high-speed settling differential amplifier of the present embodiment has an input amplification stage 60 having differential input terminals 100 and 102.
0, an output amplification stage 800 having an output terminal 106, a phase compensation capacitor 300, a feedback circuit 500, and a bias voltage source terminal 104.

The input amplification stage 600 includes a differential input transistor pair composed of n-type MOS transistors 200 and 202, and an n-type bias current source MOS transistor 204.
And an active load transistor pair composed of p-type MOS transistors 206 and 208.

Further, the output amplification stage 800 is the input amplification stage 6
A p-type MOS output transistor 210 controlled by the output of 00 and an n-type MOS constant current source transistor 212 are connected in series, and a phase compensation capacitor 300 is provided between the output of the input amplification stage 600 and the output terminal 106. It is connected to and prevents illegal oscillation of the circuit due to phase rotation and compensates for stable operation.

Further, the feedback circuit 500 includes an input transistor pair composed of p-type MOS transistors 400 and 402, a p-type bias current source MOS transistor 404, and
a p-type reference voltage source MOS transistor 408 for applying a reference voltage to the gate of the p-type MOS transistor 402, and n.
-Type MOS transistors 416 and 422, and a first current-voltage conversion circuit, and n-type MOS transistors 414 and
The input amplification stage 600 is controlled by the output of the second current-voltage conversion circuit consisting of 420 and the first current-voltage conversion circuit.
N-type feedback circuit that increases the bias current of the input amplification stage 600 by being controlled by the first output MOS transistor 424 of the n-type feedback circuit that increases the bias current and the output of the second current-voltage conversion circuit. Second output MOS transistor 426, a p-type MOS transistor 406 that applies a bias voltage to the p-type bias current source MOS transistor 404, an n-type MOS transistor 410 that supplies a bias current to the MOS transistor 406, and a MO
An n-type M that gives a bias current to the S transistor 408
It is composed of an OS transistor 412.

The drain currents of the transistors 408 and 206 and the W of each transistor when there is no difference between the voltages input to the input terminals 100 and 102.
/ L (W: channel width of the gate of the MOS transistor,
L: channel length of the gate) and the input transistor 4 of the feedback circuit 500 are designed to have the same ratio.
A reference voltage to be supplied to 02 is generated. Transistor 41
4 and 416 are 1/2 of the current flowing through the transistor 404.
When the size is designed such that a constant current of more than twice and less than one time can flow, and there is no difference in the voltage input to the input terminals 100 and 102, the output currents from the drains of the transistors 400 and 402 are the same as those of the transistors 416 and 414. Since it does not flow to the transistors 422 and 420, the drain voltage of the transistors 422 and 420 becomes equal to or lower than the threshold voltage of the output transistors 424 and 426, the transistors 424 and 426 are turned off, and the input amplification stage 600 It works so that the bias current does not increase. As a result, the power consumption during normal operation is set to the minimum.

With the above configuration, the input terminals 100 and 10
When the input voltage of the input terminal 102 is larger than the input voltage of the input terminal 100, a difference occurs in the voltages input to the two terminals,
The output current from the drain of the transistor 400 is increased, the transistors 422 and 424 are turned on and current flows, the bias current of the input amplification stage 600 is increased, and high-speed settling is possible.

When the input voltage at the input terminal 102 becomes lower than the input voltage at the input terminal 100, the output current from the drain of the transistor 402 increases, the transistors 420 and 426 turn on and a current flows, and the input amplification. This has the effect that the bias current of the stage 600 is increased to enable high-speed settling.

Therefore, when the input signal of the fast changing voltage is applied to the input terminals 100 and 102, it is transmitted to the differential amplifying transistors 400 and 402 of the feedback circuit 500 in accordance with the change and corresponds to the transmitted current. When the voltage changes more than the threshold voltage of the output transistors 424 and 426, a current corresponding to the input signal is input to the input amplification stage 6
00, the input amplification stage 600 can perform high-speed settling by simply supplying a necessary current instantaneously, and prevent wasteful consumption of power.

[Second Embodiment] FIG. 2 is a circuit diagram of a second embodiment of the present invention. The difference between this embodiment and the first embodiment is that the current-voltage conversion circuit of the feedback circuit 500 is composed of resistors 430 and 432. Since the input amplification stage 600 and the output stage 800 of this embodiment are the same as those of the first embodiment, duplicate description will be omitted.

The resistances 430 and 432 are equal to or lower than the threshold voltage (threshold voltage) of the output MOS transistors 424 and 426 of the feedback circuit 500 when half the current flowing through the p-type MOS transistor 404 flows. To design.

When the input voltage of the input terminal 102 is higher than the input voltage of the input terminal 100, the output current from the drain of the MOS transistor 400 increases, the voltage of the resistor 432 increases, and the threshold of the MOS transistor 424 increases. When the voltage becomes larger than the voltage, the MOS
A current flows through the transistor 424, and a supplemental current is supplied to the steady current according to the input voltage.

When the input voltage of the input terminal 100 is larger than the input voltage of the input terminal 102, the output current from the drain of the MOS transistor 402 increases, the voltage of the resistor 430 increases, and the threshold voltage of the MOS transistor 426 increases. When it becomes larger, a current flows through the MOS transistor 426, and a supplementary current added to the steady current corresponding to the input voltage is supplied.

Naturally, when the input voltage of the input terminal 100 and the input voltage of the input terminal 102 match, the current flowing through the input amplification stage is set to be minimum.

In this way, when a differential voltage above a certain level is input to the input voltage, the bias current of the input amplification stage 600 increases, enabling high-speed settling, and a differential voltage below a certain level is input. In this case, the settling can be achieved by a steady current, and as a result, the settling speed can be increased and low power consumption can be achieved.

As a result, in the first embodiment, the increase in the output current of the input transistor of the feedback circuit 500 and the increase in the output current of the output transistor of the feedback circuit 500 are in a proportional relationship, whereas in the present embodiment. in the form, the output current increases in accordance with V _GS -I _D characteristic of the MOS transistor, that is an increase in the output current of the input MOS transistors 400 and 402 of the feedback circuit 500, increasing the square characteristics of the output current of the feedback circuit 500 And the effect that a steeper settling can be realized.

[0037]

As described above, the differential amplifier of the present invention has an effect that a high-speed settling can be realized without increasing the steady current as compared with the conventional example.

[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 second embodiment of the present invention.

FIG. 3 is a circuit diagram of a conventional example related to the present invention.

[Explanation of symbols]

100,102 Input terminal 104 Bias voltage terminal 106 Output terminal 200,202 Input amplification stage input transistor 204 Bias current source transistor 206,208 Active load transistor 210,212 Output transistor 300 Phase compensation capacitance 400,402 Feedback circuit input transistor 408 Reference voltage Generation transistors 416, 420 Output transistors 414, 416, 420, 422 of feedback circuit Current-voltage conversion circuit transistors 430, 432 Current-voltage conversion resistance

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H03F 1/00-3/72

Claims (4)

(57) [Claims] 1. A differential input stage that operates with a steady current, a differential amplification output stage that receives and outputs the output of the differential input stage, and a coupling between the differential input stage and the differential amplification output stage. In a differential amplifier including a phase compensation circuit that compensates for stable operation of the circuit, a differential detection stage that detects a difference in input voltage of the differential input stage, and a differential detection stage of the differential detection stage. A current / voltage converter for converting a current output into a voltage output, and
The differential input stage comprises a MOS transistor pair and the MO transistor pair, and a current feedback unit for making a supplementary current of the differential input stage when the output of the voltage conversion unit becomes equal to or higher than a threshold voltage.
Constant current source MO connected to common source of S transistor pair
An S-transistor and an active load transistor pair of a current mirror configuration connected to each drain of the MOS transistor pair. The differential amplification output stage has an output MO having a gate connected to one of the active load transistor pair.
The phase compensation circuit includes an S transistor and a constant current source MOS transistor serving as a load of the output MOS transistor, and the phase compensation circuit is connected between one of the active load transistor pair and the output of the output MOS transistor. The motion detection stage has a feedback differential transistor pair that receives the output of the differential input stage at one input terminal and uses the other input terminal as a reference voltage, and the current / voltage conversion unit includes the feedback differential transistor pair. consists load conversion MOS transistor pair is directly connected to the connected gate and drain, respectively,
And wherein the current feedback unit is composed of a feedback MOS transistor pairs respectively connected to the gate and drain of said conversion MOS transistor pair, it is connected to the drain of the feedback MOS transistor pair to the current supply portion of the differential input stage Differential amplifier to do. 2. The differential amplifier according to claim 1 , wherein a constant current source MOS transistor pair is connected as a load of the feedback differential transistor pair, and a constant voltage bias is applied to the gate of the constant current source MOS transistor pair. A differential amplifier characterized in that a voltage is supplied and the bias voltage is supplied to the gate of a constant current source MOS transistor serving as a load of the output MOS transistor. 3. A differential input stage operating with a steady current, and the difference.
Differential amplification output stage that receives and outputs the output of the dynamic input stage,
Stable coupling circuit between the differential input stage and the differential amplification output stage
Differential consisting of a phase compensation circuit that compensates
Te amplifier smell, a difference in the input voltage of the differential input stage occurs
Of the differential detection stage and the current output of the differential detection stage
A current / voltage converter for converting force into a voltage output, and
The output of the voltage converter exceeds the threshold voltage.
And a current feedback section for supplying supplemental current to the differential input stage.
The differential input stage includes a MOS transistor pair and the MO transistor pair.
Constant current source MO connected to common source of S transistor pair
S transistor and each drain of the MOS transistor pair
In-connected current mirror active load transitions
And a differential amplifier output stage
Output MO with gate connected to one of load transistor pair
S transistor and load of the output MOS transistor
And a constant current source MOS transistor
The phase compensation circuit is connected to one of the active load transistor pair and the front side.
The differential detection stage has a feedback differential transistor pair connected to the output of the output MOS transistor and receiving the output of the differential input stage at one input terminal and using the other input terminal as a reference voltage. The current / voltage conversion unit includes resistors connected to the loads of the feedback differential transistor pair, and the current feedback unit includes a feedback MOS transistor pair in which the resistors are connected between a gate and a source. A differential amplifier characterized in that a drain of a feedback MOS transistor pair is connected to a current supply section of the differential input stage. 4. A pair of input transistors having respective gates as input terminals and sources commonly connected to each other, a current source transistor connected to a common source of the pair of input transistors to supply a bias current, and the pair of input transistors. Input the output current from the drain of each to the drain,
An active load transistor pair having one drain connected to a common gate, an output amplification stage for inputting and amplifying an output voltage of the active load transistor pair, an output of the active load transistor pair and an output terminal of the output amplification stage A differential amplifier having a phase compensation capacitance connected between the first and second input transistor pairs, wherein the input transistor pair has a drain connected to a common gate of the active load transistor pair and one drain of the active load transistor pair. An input transistor and a second input transistor having a drain connected to the other drain of the active load transistor pair, and a third transistor having a common gate voltage of the active load transistor pair as one input. The other input is connected to the gate of the active load transistor pair when the input voltages of the input transistor pair are equal. A transistor pair of a feedback circuit having a source commonly connected with a fourth transistor having a reference voltage equal to the voltage as the other input, and a current of the feedback circuit for supplying a bias current to the common source of the transistor pair of the feedback circuit. source and the transistor, the third, first, second current to be converted to respective voltage inputs an output current from the drain of the fourth transistor - a pair of current having a voltage conversion circuit - voltage conversion circuit , The pair of currents −
The output voltage of the voltage conversion circuit has an output transistor pair of the feedback circuit in which the output voltage of the feedback circuit is connected to each gate and the drain is connected to the common source of the pair of input transistors, and the output voltage of the output voltage of the current-voltage conversion circuit is , When the input voltages of the input transistor pair are equal, do not increase the bias current of the input transistor pair below the threshold voltage of the output transistor pair of the feedback circuit,
When the input voltage of the first input transistor is higher than the second input transistor, the drain current of the third transistor is increased to turn on one current-voltage conversion circuit of the feedback circuit, When the input voltage of the input transistor is smaller than the second input transistor, the drain current of the fourth transistor is increased to turn on the other current-voltage conversion circuit of the feedback circuit ,
A differential amplifier characterized by increasing a bias current of the input transistor pair.