JP2001274640A - Amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an amplifier circuit with a small resistance and a small capacitance, which has a small area and can reduce an offset. SOLUTION: A differential amplifier circuit consists of transistors(TRs) M2, M1 whose gate electrodes are used for positive and negative input terminals, resistive elements RN1, RP1, and a constant current source I1. An amplifier having bipolar inputs and outputs amplifies outputs of the differential amplifier circuit to provide the amplified outputs to positive and negative output terminals. An amplifier circuit consisting of a resistor RP3, TRs M3, M4 and a constant current source I2 and a capacitor CP having an equivalent capacitance multiplied by a multiple of a gain eliminates an AC component of signals from the positive and negative output terminals and an amplifier circuit consisting of a resistor RN3, TRs M8, M7 and a constant current source I4 and a capacitor CN having an equivalent capacitance multiplied by a multiple of a gain eliminates the AC component of the signals from the positive and negative output terminals. The signals whose AC component is eliminated are negatively fed back to the inputs of the amplifier with a differential amplifier circuit consisting of TRs M5, M6 and a constant current source I3. The negative feedback can reduce the offset of the amplifier. Since each equivalent capacitor is multiplied by a gain with the mirror effect, a smaller resistance and a smaller capacitance are enough to realize the same time constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an amplifier circuit,
In particular, it relates to an amplifier circuit having a small size and a large time constant.

[0002]

2. Description of the Related Art First, in order to clarify the background of the present invention, an example of a conventional amplifier circuit is shown in FIG. This circuit is described in, for example, TH Hu and P. R. Gr
ay, "A Monolithic 480 Mb / s
Parallel AGC / Decision / Clo
ck-Recovery Circuit in 1.
2um CMOS ", IEEE J. Solid-St
ate Circuit, vol. SC-28, p
p. 1314-1320, Dec. 1993, etc.

In the circuit shown in FIG. 5, a transistor M1 has a gate electrode connected to a negative input terminal, a drain electrode commonly connected to one end of a load resistance element RN1, a positive input of an amplifier, and a drain electrode of a transistor M6, and a source electrode connected thereto. The source electrode of the transistor M2 and one end of the current source I1 are commonly connected. The transistor M2 has a gate electrode connected to the positive input terminal and a drain electrode commonly connected to one end of the load resistance element RP1, the negative input of the amplifier, and the drain electrode of the transistor M5. The other end of the constant current source I1 is connected to a reference potential. The other end of the load resistor RN1 is connected to a power supply. The other end of the load resistor RP1 is connected to a power supply. The amplifier amplifies the potential difference between the positive and negative inputs and outputs it to the positive and negative output terminals. Resistance RP
3 has one end connected to the negative output of the amplifier and the other end commonly connected to the gate electrode of the transistor M5 and one end of the capacitor CA. The source electrode of the transistor M5 is commonly connected to the source electrode of the transistor M6 and one end of the constant current source I3. The other end of the constant current source I3 is connected to a reference potential. Resistance R
N3 has one end connected to the positive output of the amplifier and the other end commonly connected to the gate electrode of the transistor M6 and one end of the capacitor CA.

[0004] Transistors M1, M2, resistors RN1, R
The circuit composed of P1 and the constant current source I1 is a so-called differential amplifier in which the voltage difference between the positive and negative inputs is amplified and the resistors RN1 and RP1
Of the potential difference. The amplification factor can be represented by a product of gm of the transistors M1 and M2 and resistance values of the resistors RN1 and RP1. The potential difference between the resistors RN1 and RP1 is amplified by the next-stage amplifier to obtain positive and negative outputs.

In general, even if the input is 0, the output of the amplifier is not exactly 0, and a DC offset voltage is output. Resistance RP3, RN3, capacitance CA, transistor M
5, M6, a constant current source I3 is called a so-called offset cancel circuit, and the resistors RN1 and RP1
, Transistors M5 and M6, and a constant current source I3 to form a differential amplifier circuit.
The AC component is removed by the RN3 and the capacitor CA, and the transistor M
5 and M6, only the DC component is negatively fed back to the input of the amplifier. Even if a DC output occurs in the positive and negative outputs, negative feedback is applied in a direction to reduce the DC component. Therefore, the DC output when the input is 0, that is, the offset can be reduced.

[0006]

The offset is a DC component, and the signal component to be amplified is an AC. In the offset cancel circuit, it is required to cancel DC as much as possible so as not to affect the signal component as much as possible. In order to extract only the DC component from the positive and negative outputs, it is necessary to increase the element values of the resistors RP3, RN3 and the capacitor CA, and to increase the time constant determined by the product of the resistance value and the capacitance value. Increasing the resistance value or the capacitance value has a problem that an occupied chip area increases, especially in an integrated circuit.

[0007]

Means for Solving the Problems In order to solve the problems of the prior art, the present invention employs the means shown in FIG. The gate electrode of the transistor M4 is input and the transistor M4
4 as a drive stage, a transistor M3 as a load stage, and a capacitor CP connected to an input / output of an amplifier circuit that outputs a drain electrode of the transistor M4. The sum of the drain currents of the transistors M3 and M4 flows through the constant current source I2. When the gate electrode of the transistor M4 changes, the transistor M4
Transistors M3 and M4 in which the drain current of transistor 4 changes
Is the current of the constant current source I2 and does not change. Therefore, if the drain current of the transistor M4 decreases, the drain current of the transistor M3 increases by the decrease in the current. When the drain current of the transistor M3 changes, the voltage between the gate and the source of the transistor M3 changes. That is, the transistors M4 and M3 and the constant current source I
2 constitutes an amplifier circuit in which the gate electrode of the transistor M4 is input and the drain electrode of the transistor M4 is output. Since the capacitance CP is connected between the gate electrode and the drain electrode of the transistor M4, the capacitance CP is connected between the input and the output of the amplifier circuit. The capacitance connected between the input and the output of the amplifier circuit has an effect called a so-called Miller capacitance. The Miller capacitance is obtained by multiplying the equivalent capacitance value seen from the input by the gain of the original capacitance value. Therefore, the resistance RP
The time constant viewed from one end of No. 3 is the capacitance value of the capacitance CP × the resistance R
The resistance value of P3 × (the gain of the amplifier circuit of the transistors M4 and M3) is obtained, and a time constant twice as large as the gain without the amplifier circuit can be obtained. Therefore, in order to obtain the same time constant, a small capacitance value or a small resistance value can be used.

FIG. 1 shows a differential amplifier circuit,
3. The functions of the transistors M7 and M8 and the constant current source I4 are as follows.
The symmetrical resistors RP3, transistor M4,
M3, the same function as the constant current source I2.

[0009]

FIG. 1 shows a circuit configuration of the present invention.

A differential amplifier circuit is composed of transistors M2 and M1, whose gate electrodes are positive and negative input terminals, resistance elements RN1 and RP1, and a constant current source I1. The output of the differential amplifier circuit is amplified by an amplifier circuit having positive and negative inputs and outputs and output to positive and negative output terminals. An AC component is removed from the positive and negative output terminals by a resistor RP3 and a capacitor CP having an equivalent capacitance value multiplied by a gain in an amplifier circuit of the transistors M3, M4 and the constant current source I2, thereby removing a resistor RN3, transistors M8, M7, A capacitor C having an equivalent capacitance value multiplied by a gain in the amplifier circuit of the constant current source I4
Remove the alternating current with N. The DC component with the AC component removed is
A differential circuit of transistors M5, M6 and constant current source I3,
Negative feedback is provided to the input of the amplifier to reduce offset.

[0011]

FIG. 1 shows a circuit configuration of the present invention. The transistor M1 has a gate electrode connected to the negative input terminal, a drain electrode commonly connected to one end of the load resistance element RN1, the positive input of the amplifier and the drain electrode of the transistor M6, and a source electrode connected to the source electrode of the transistor M2 and the current source. Commonly connected to one end of I1. The transistor M2 has a gate electrode connected to the positive input terminal and a drain electrode connected to the load resistance element RP.
1 and the negative input of the amplifier and the drain electrode of the transistor M5. The other end of the constant current source I1 is connected to the reference potential. The other end of the load resistance element RN1 is connected to a power supply. The other end of the load resistance element RP1 is connected to a power supply.

The amplifier amplifies the potential difference between the positive and negative inputs and outputs it to the positive and negative output terminals. The resistor RP3 has one end connected to the negative output of the amplifier and the other end commonly connected to the gate electrode of the transistor M5, the gate electrode of the transistor M4, and one end of the capacitor CP. The transistor M4 has a drain electrode commonly connected to the other end of the capacitor CP, the drain electrode and gate electrode of the transistor M3, and the other end of the constant current source I2, and a source electrode connected to a power supply. The transistor M3 has a source electrode connected to a power supply. The other end of the constant current source I2 is connected to the reference potential. The transistor M5 has a source electrode commonly connected to the source electrode of the transistor M6 and one end of the constant current source I3. The other end of the constant current source I3 is in contact with the reference potential.

The resistor RN3 has one end connected to the positive output of the amplifier and the other end commonly connected to the gate electrode of the transistor M6, the gate electrode of the transistor M7, and one end of the capacitor CN. The transistor M7 has a drain electrode commonly connected to the other end of the capacitor CN, the drain electrode and gate electrode of the transistor M8, and the other end of the constant current source I4, and a source electrode connected to a power supply. The transistor M8 has a source electrode connected to a power supply. The other end of the constant current source I4 is connected to the reference potential.

Transistors M1, M2, resistors RN1, R
The circuit constituted by P1 and the constant current source I1 is a so-called differential amplifier circuit, and outputs a positive / negative input potential difference as a potential difference between voltages across the resistors RN1 and RP1. The amplification factor k is equal to gm of the transistors M1 and M2 × resistance values RP1 and RN1. The same configuration is used for transistors M5, M6, and resistor RN.
1, RP1 and constant current source I3. The potential difference between the voltages of the gate electrodes of the transistors M5 and M6 is equal to the resistance RN.
1, and output as a potential difference between the voltages at both ends of RP1. The amplification factor h is gm × resistance value RP of the transistors M5 and M6.
1, RN1. Since the resistors RN1 and RP1 are shared, the potential difference between the voltages at both ends of the resistors RN1 and RP1 is
Amplified positive and negative input voltages and transistors M5 and M6
Are obtained by amplifying the amplified potential difference of the gate electrode.

The amplifier shown in FIG. 1 has resistors RN1 and RP1 respectively.
The positive and negative inputs connected to one end are amplified by an amplification factor G to produce positive and negative outputs. When the potential difference between the positive and negative outputs increases (the positive output voltage increases and the negative output decreases),
The voltage of the gate electrode of the transistor M6 rises and the resistance RN
1 increases, the voltage of the gate electrode of the transistor M5 decreases, and the current flowing through the resistor RP1 decreases. The voltage at one end of the resistor RN1 connected to the positive input of the amplifier tends to decrease, and the voltage at one end of the resistor RP1 connected to the negative input of the amplifier tends to increase. That is, when the potential difference of the output of the amplifier increases, negative feedback is applied so as to reduce the potential difference of the output.

A resistor RP3, a capacitance CP, a transistor M
The circuit composed of 3, M4 and the constant current source I2 has a function of a filter for extracting a DC component other than a signal component from the output. The capacitor CP is connected to the input / output of an amplifier circuit that receives the gate electrode of the transistor M4 as an input, uses the transistor M4 as a driving stage, uses the transistor M3 as a load stage, and uses the drain electrode of the transistor M4 as an output. The sum of the drain currents of the transistors M3 and M4 flows through the constant current source I2. When the gate electrode of the transistor M4 changes, the drain current of the transistor M4 changes. The sum of the currents flowing through the transistors M3 and M4 does not change because the current is the constant current source I2. If the drain current of the transistor M4 decreases, the drain current of the transistor M3 increases by the decrease in the current. When the drain current of the transistor M3 changes, the voltage between the gate and the source of the transistor M3 changes. That is, the transistors M4 and M3 and the constant current source I2 input the gate electrode of the transistor M4,
An amplifier circuit using the drain electrode of the transistor M4 as an output is configured. The amplification factor is gm / g of transistor M4.
Gm of the transistor M3.

Since the capacitance CP is connected between the gate electrode and the drain electrode of the transistor M4, in other words, the capacitance CP is connected between the input and the output of the amplifier circuit. The capacitance connected between the input and the output of the amplifier circuit has an effect called a so-called Miller capacitance. The Miller capacitance is obtained by multiplying the equivalent capacitance value seen from the input by the gain of the original capacitance value. Therefore, the time constant viewed from one end of the resistor RP3 is the capacitance value of the capacitor CP × the resistance value of the resistor RP3 × (transistor M
4, the gain of the amplifier circuit of M3), and a time constant twice the gain can be equivalently obtained as compared with the case where there is no amplifier circuit. Therefore, in order to obtain the same time constant, a small capacitance value or a small resistance value can be used.

Resistance RN3, capacitance CN, transistor M
8, M7 and the constant current source I4 are symmetrical to the resistor RP3, the capacitance CP, the transistors M3 and M4, and the constant current source I2, and perform the same function. Hereinafter, only one of them will be described.

Resistance RP3, capacitance CP, transistor M
3, M4, and the time constant (1 /
ω) is (1 / ω) = RP3 * CP * (gm of transistor M4
/ Gm of transistor M3) Amplification factor k of a circuit composed of transistors M1, M2, resistors RN1, RP1, and constant current source I1, transistor M5
Assuming that the amplification factor h of the circuit constituted by M6, the resistors RN1, RP1, and the constant current source I3 and the amplification factor G of the amplifier are shown in FIG. 2, the circuit of FIG. 1 is represented by an equivalent circuit. FIG.
And off represents the offset of the amplifier.

FIG. 3 shows the characteristics of the equivalent circuit of FIG. FIG.
The left of indicates the relationship between the input in and the output out. The gain is small where the input frequency is small. FIG. 3R shows the relationship between the offset off and the output. When the frequency is high, the offset off is output as it is, but when the frequency is low, the offset off is 1 / (1 + G
h). A signal component is input to the input in. In order to amplify as low a signal component as possible, it is necessary to increase the time constant (1 / ω). To increase the time constant, the resistance and capacitance may be increased. However, in an integrated circuit, increasing the resistance and capacitance is not preferable because the occupied area increases. In the present invention, in order to increase the time constant, the gain (gm of transistor M4 / gm of transistor M3) of the circuit for creating the Miller capacitance may be increased.

FIG. 4 shows the circuit of FIG.
, M2, resistors RN1, RP1, and a constant current source I1 are connected to transistors M1, M2, M
1A, M2A, M1B, M2B, resistance elements RN1, RP
1, a constant current source I1. Resistance element RP
1, RN1 is constituted by a so-called diode-connected transistor in which a gate electrode and a drain electrode are commonly connected. M2A and M2B and M1A and M1B constitute a so-called current mirror circuit in which gate electrodes are connected in common. Since the gate electrodes are commonly connected, the transistors M2A and M2B and the transistor M1A
And the current flowing through the transistor M1B depends on the size ratio of the transistors. The characteristics of the circuit in FIG. 4 can be similarly expressed in FIGS.

In the circuit shown in FIG. 4, the polarity of the input transistor is reversed from that shown in FIG. Transistors M5, M6,
Using the differential circuit of the constant current source I3, the resistance elements RP1, R
If N1 is composed of a diode-connected transistor,
Transistors M5 and M6 and transistors RN1 and RP1
Must be reversed. In the configuration in FIG. 1, the polarity of the transistors RN1 and RP1
There is no choice but to have polarities of 1 and M2. In the circuit configuration of FIG. 4, the polarity of the transistors RP1 and RN1 and the input transistor can be made the same.

The circuit of FIG. 6 is an example of the amplifier in the circuits of FIGS. 1, 4 and 5. There are countless methods for configuring the amplifier, and the circuit of FIGS. 1 and 4 does not limit the effects of the present invention even if the circuit configuration of the amplifier that can be used is not particularly limited.

The circuit shown in FIG. 6 is a two-stage cascade-connected differential amplifier circuit, which constitutes an amplifier. The first stage differential amplifier circuit
This is a general configuration including transistors M10 and M11, resistors RP4 and RN4, and a constant current source I5. The second-stage differential amplifier circuit also includes transistors M12, M13M14, M
15 and a general current source I6. 2
The load of the differential amplifier circuit of the stage is changed by transistors M14 and M1.
5 is a characteristic of this amplifier. Figure 1
When the circuit of FIG. 6 is used as the amplifier of the circuit of FIG. 4, the transistors M4 and M7 for the mirror capacitance of the circuits of FIGS.
And the polarities of M15 and M16 in FIG. 6 can be made equal. Since the polarities are the same, a gate voltage is applied on the basis of the power source, and the gate-source voltages of the transistors M4, M7, M15 and M16 can be made equal. Therefore, even if the power supply voltage changes, the gate-source voltage of the transistors M4 and M7 does not change. When the gate-source voltage is constant, the current flowing through the transistors M4 and M7 does not change. Therefore, there is an effect that it is not necessary to change the current values of the constant current sources I2 and I4 with the power supply voltage. of course,
Instead of a two-stage cascaded differential amplifier circuit, a transistor M
Even if the amplifier is constituted by a single-stage differential amplifier circuit of 12, M13, M14, M15 and the constant current source I6, the effect that the current value of the constant current source I2 does not need to be changed by the power supply voltage is the same.

It is needless to say that the circuit operation is equivalent even if the polarities of all the transistors are exchanged in FIGS. 1 and 4 and the polarities of the power supply voltage are changed.

[0026]

As described above, the transistor M
4, M3 and the constant current source I2 constitute an amplifier circuit in which the gate electrode of the transistor M4 is input and the drain electrode of the transistor M4 is output. Since the capacitance CP is connected between the gate electrode and the drain electrode of the transistor M4, the capacitance CP is connected between the input and the output of the amplifier circuit. The capacitance connected between the input and output of the amplifier circuit is
There is an effect called a so-called mirror capacitance. The mirror capacity is
The equivalent capacitance value seen from the input is multiplied by the gain of the original capacitance value. Therefore, the time constant viewed from one end of the resistor RP3 is the capacitance value of the capacitor CP × the resistance value of the resistor RP3 × (transistor M
4, the gain of the amplifier circuit of M3), and a time constant twice the gain can be equivalently obtained as compared with the case where there is no amplifier circuit. Therefore, in order to obtain the same time constant, a small capacitance value or a small resistance value can be used.

The gain of the circuit for the Miller capacitance constituted by the transistors M4, M3 and the constant current source I2 is:
As described above, gm of transistor M4 / gm of transistor M3 can be expressed. Transistor g
Since the ratio of m can easily be several times as large as the size and current of the transistor, the capacitance value and the resistance value can be reduced to a fraction.
Can be.

[Brief description of the drawings]

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

FIG. 2 is a characteristic diagram of the embodiment of the present invention.

FIG. 3 is a characteristic diagram of the embodiment of the present invention.

FIG. 4 is a circuit diagram showing an embodiment of the present invention.

FIG. 5 is an amplifier circuit according to a conventional technique.

FIG. 6 shows a conventional amplifier.

[Explanation of symbols]

I1, I2, I3, I4, I5, I6 Constant current source M1, M2, M3, M4, M5, M6, M7, M8 Transistor M1A, M1B, M2A, M2B Transistor M10, M11, M12, M13, M14, M15 Transistor RP1, RN1, RP3, RN3, RP4, RN4 Resistance CP, CN, CA Capacity

Continued on the front page F term (reference) 5J066 AA01 AA12 CA13 CA92 FA20 HA09 HA17 HA19 HA25 HA29 KA05 KA25 MA13 MA21 ND01 ND11 ND22 ND23 PD02 TA01 TA03 5J090 AA01 AA12 CA13 CA92 DN02 FA20 HA09 HA17 HA19 HA25 HA29 HN06 KA05 TA01 TA03 5J091 AA01 AA12 CA13 CA92 FA20 HA09 HA17 HA19 HA25 HA29 KA05 KA25 MA13 MA21 TA01 TA03

Claims (1)

[Claims] 1. A gate electrode is connected to a negative input terminal, a drain electrode is commonly connected to one end of a load resistance element RN1, a positive input of an amplifier, and a drain electrode of a transistor M6, and a source electrode is connected to a source electrode of a transistor M2 and a current source. A transistor M1 commonly connected to one end of I1; a transistor M2 having a gate electrode connected to the positive input terminal and a drain electrode commonly connected to one end of the load resistance element RP1 and the negative input of the amplifier and the drain electrode of the transistor M5; , A constant current source I1 having the other end connected to the reference potential, a load resistance element RN1 having the other end connected to the power supply, and a load resistance element RP1 having the other end connected to the power supply. The amplifier for outputting to the output terminal, one end connected to the negative output of the amplifier, and the other end connected to the gate electrode of the transistor M5 and the gate of the transistor M4. A resistor RP3 commonly connected to the gate electrode and one end of the capacitor CP, and a drain electrode commonly connected to the other end of the capacitor CP, the drain electrode and the gate electrode of the transistor M3, and the other end of the constant current source I2, and the source electrode to the power supply , A transistor M3 whose source electrode is connected to a power supply, a constant current source I2 whose other end is connected to a reference potential, and a source electrode common to the source electrode of the transistor M6 and one end of the constant current source I3. Connected transistor M5
A constant current source I3 having the other end connected to the reference potential, one end connected to the positive output of the amplifier, and the other end connected to the gate electrode of the transistor M6, the gate electrode of the transistor M7, and the capacitor CN.
And a transistor M7 having a drain electrode commonly connected to the other end of the capacitor CN, the drain electrode and gate electrode of the transistor M8, and the other end of the constant current source I4, and a source electrode connected to the power supply. An amplifier circuit comprising a transistor M8 having a source electrode connected to a power supply, a constant current source I4 having the other end connected to a reference potential, and the transistor M6.