KR20060099976A - Operational trans-conductance amplifier using current sink - Google Patents

Abstract

The present invention relates to an operational transconductance amplifier, and more particularly, to an operational transconductance amplifier using a current sink capable of minimizing standby current to minimize power consumption. The operational transconductance amplifier according to the present invention includes a bias unit, a differential input unit, a first current sink, a second current sink, a first current mirror, a second current mirror, and an output terminal. According to the present invention, the frequency compensation is performed, so that the dominant pole characteristic is good and a high DC voltage gain can be obtained while having a small standby current. Its high DC voltage gain and high power efficiency allow it to be used in switch-capacitor circuits requiring low voltage and high speed.

OTA, standby current, current sink, current mirror, differential input, DC voltage gain

Description

Operational trans-conductance amplifier using current sink

1A is a circuit diagram of a conventional current mirror operational transconductance amplifier.

1B is a circuit diagram of an operational transconductance amplifier with a cascode circuit added to the output of the operational transconductance amplifier shown in FIG. 1A.

2 is a circuit diagram of an operational transconductance amplifier using a current sink according to an embodiment of the present invention.

3 is a circuit diagram of an operational transconductance amplifier using a current sink according to another embodiment of the present invention.

4 is a frequency response result diagram using a conventional operational transconductance amplifier.

5 is a frequency response result using an operational transconductance amplifier according to the present invention.

<Explanation of symbols for the main parts of the drawings>

100: bias unit 110: differential input unit

120: first current mirror 130: second current mirror

140: output terminal

200, 300: Current sink

310: first current sink

The present invention relates to an operational trans-conductance amplifier (OTA), which is referred to as an operational transconductance amplifier (hereinafter, referred to as an "operational transconductance amplifier"). An operational transconductance amplifier.

Operational transconductance amplifiers are essential blocks that play a central role in switch-capacitor circuits such as analog filters or oversampled delta-sigma data converters. The wide bandwidth, high gain, high slew rate, and small quiescent current of the operational transconductance amplifier itself are essential for a system using an operational transconductance amplifier to achieve good results.

1A is a circuit diagram of a conventional current mirror operational transconductance amplifier. Referring to FIG. 1A, the current mirror operational transconductance amplifier includes a bias unit 100, a differential input unit 110, a first current mirror 120, a second current mirror 130, and an output terminal 140.

The bias unit 100 generates a bias current, which is the basis of output current generation in the operational transconductance amplifier, using the bias voltage and supplies the bias current to the differential input unit 110. The differential input unit 110 includes a first input terminal and a second input terminal and receives two voltage signals, that is, a first voltage and a second voltage. Here, the first voltage and the second voltage may be both a positive voltage and a negative voltage, respectively. The bias current received from the bias unit 100 is divided into a first bias current and a second bias current according to each voltage magnitude. The first current mirror 120 mirrors the first bias current by the first voltage input received through the first input terminal. The second current mirror 130 mirrors the second bias current caused by the second voltage input received through the second input terminal. An output current having a magnitude equal to the difference between the first bias current and the second bias current mirrored by the first current mirror 120 and the second current mirror 130 is output through the output terminal 140.

Hereinafter, a description will be given based on the transistors shown in FIG. 1A, and it is assumed that the first bias current is a positive current and the second bias current is a negative current. In the current mirror op amp, the negative current from transistor M1 is repeated to transistors M3-M5-M7-M8, and the positive current from transistor M2 is repeated to transistors M4-M6 and then mirrored to the output terminals. The difference component of the current is output. Here, the transistors M3 and M4 are connected in the form of a diode so that their small signal equivalent resistances, i.e., the loads of the transistors M1 and M2, are very small at 1 / g _m , corresponding to the first pole value. This becomes very loud. On the other hand, the value of the second pole formed by the high output resistance of the output stage and the load capacitance C _L (not shown) is so small that the second pole is selected as the dominant pole and stabilizes the circuit. That is, in the current mirror operational transconductance amplifier shown in FIG. 1A, as the load capacity increases, the phase margin increases and the circuit is stabilized. In addition, although the current mirror arithmetic transconductance amplifier shown in FIG. 1A has been widely used due to the wide output voltage swing, there is a problem in that the DC gain is not high enough and power efficiency is low.

To achieve higher DC gains, the output stages of existing op amps can be modified with cascode circuitry to achieve larger output resistance. FIG. 1B is a circuit diagram of an operational transconductance amplifier in which a cascode circuit is added to an output terminal of the operational transconductance amplifier shown in FIG. 1A. As shown in FIG. 1B, the transistor M30 is connected between the output terminal of the transistor M6 and the output terminal of the conventional operational transconductance amplifier, and the transistor M20 is connected between the transistor M8 and the output terminal to form a cascode circuit. The voltage gain can be increased by two stages of amplification, but the output swing is limited by the additionally coupled transistors M20 and M30 that operate in the saturation region. Therefore, it cannot be used in a wide voltage circuit, which is a big problem. In addition, the current mirror arithmetic transconductance amplifier shown in Figs. 1A to 1B limits the maximum output current Io, max output through the output terminal, resulting in a slew rate as shown in Equation (1).

- 수학식 (1)

Equation (1)

It and C _load (not shown) refer to bias current and load capacitor, respectively. Here, the alphabet written under the NMOS transistors shown in FIGS. 1A to 3 indicates the size of the transistors (a ratio of width and length, W / L; hereinafter referred to as 'W / L'). In other words, the W / L ratios of the transistors M6 and M4 in FIG. 1 are A to B, respectively. Here, the standby current is also increased if the bias current It or the current mirroring ratio A / B is increased for higher slew rate. Recently, battery-operated portable systems have gained popularity, and the increased quiescent current is inadequate for many systems that want to maximize power efficiency. A suitable solution for obtaining a high slew rate is to raise the bias current It during slewing. However, while lowering quiescent current can maximize power efficiency, the low DC gain of conventional current mirror op amps still remains unsolved.

Accordingly, in order to solve the above problems, an object of the present invention is to provide an operational transconductance amplifier using a current sink capable of obtaining a high DC voltage gain with good dominant pole characteristics and small standby current due to frequency compensation. .

Another object of the present invention is to provide an operational transconductance amplifier using a current sink with high power efficiency.

It is still another object of the present invention to provide an operational transconductance amplifier using a current sink that can be used in a switch-capacitor circuit requiring low voltage and high speed due to high DC voltage gain and high power efficiency.

In order to achieve the above object, according to an aspect of the present invention, a bias unit for generating a bias current using a bias voltage; A first bias current including a first input terminal and a second input terminal, the bias current corresponding to a difference between a first differential voltage and a second differential voltage received through the first input terminal and the second input terminal; And a differential input unit configured to distribute the second bias current; A first current sink and a second current sink connected to the differential input to sink some of the first bias current and the second bias current; A first current mirror configured to mirror the current by receiving a current corresponding to a difference between the first bias current and the current sinked by the first current sink; A second current mirror configured to mirror the current by receiving a current corresponding to a difference between the second bias current and the current sinked by the second current sink; And an output terminal for outputting a current corresponding to a difference between the current mirrored by the first current mirror and the current mirrored by the second current mirror.

Preferably, the first current sink and the second current sink can generate a predetermined sink current by a predetermined same sink voltage, and the first current sink and the second current sink have drains respectively different from each other. The input unit may be connected to the connection portion of the first current mirror and the differential input unit to the connection portion of the second current mirror, the sink voltage may be input through a gate, and the source may include a transistor connected to ground.

Also preferably, the first current sink and the second current sink may generate sink currents having different magnitudes by different sink voltages except for the standby state. The first current sink may be characterized in that the sink voltage is the second voltage and the current sink by current mirroring a portion of the second bias current, the first current sink, the gate is the second voltage A first transistor that receives an input, a source is connected to the bias unit, and a drain thereof outputs a portion of the second bias current; And a first sink current mirror configured to receive the current output through the drain of the first transistor and mirror the current to generate the sink current.

In addition, the second current sink may be characterized in that the sink voltage is the first voltage and the current sink by current mirroring a portion of the first bias current, the second current sink, the gate is the first A second transistor configured to receive a voltage, a source connected to the bias unit, and a drain configured to output a portion of the first bias current; And a second sink current mirror configured to receive the current output through the drain of the second transistor and mirror the current to generate the sink current.

In addition, the transistor included in the operational transconductance amplifier may be formed of CMOS.

Other objects, specific advantages and novel features of the present invention will become more apparent from the following detailed description and the preferred embodiments associated with the accompanying drawings. Hereinafter, a preferred embodiment of the operational transconductance amplifier using the current sink according to the present invention will be described in detail with reference to the accompanying drawings. Hereinafter, the detailed description will be made based on a CMOS transistor, and the present invention may be applied to an NMOS, a PMOS transistor, or a JFET in addition to the CMOS. In addition, it is a matter of course that the configuration of the circuit consisting of the N-type transistor and the P-type transistor can be made by converting the P-type transistor and the N-type transistor symmetrical by those skilled in the art. The simulation of the drawings used in the following description is characterized in that it is performed by HSPICE simulation using CMOS 0.35㎛ process parameters, which of course does not limit the scope of rights.

2 is a circuit diagram of an operational transconductance amplifier using a current sink according to an embodiment of the present invention. The operational transconductance amplifier using the current sink includes a bias unit 100, a differential input unit 110, a first current mirror 120, a second current mirror 130, an output terminal 140, and a current sink 200. do.

The bias unit 100 generates a bias current using the bias voltage and supplies a bias current to the differential input unit 110.

The differential input unit 110 includes a first input terminal and a second input terminal. Among them, the first voltage is input through the first input terminal, and the second voltage is input through the second input terminal. The bias current supplied from the bias unit 100 is divided into a first bias current and a second bias current so as to correspond to a difference between the first voltage and the second voltage.

The first current sink of the current sink 200 is simultaneously connected to the connection portion of the differential input unit 110 and the first current mirror 120. In addition, the second current sink of the current sink 200 is simultaneously connected to the connection portion of the differential input unit 110 and the second current mirror 130. The first current sink and the second current sink serve to sink current corresponding to a predetermined sink voltage. The amount of sink current can be arbitrarily determined according to the sink voltage Vbias, which greatly reduces the standby current of the operational transconductance amplifier.

The first current mirror 120 and the second current mirror 130 are mirrored by receiving a current corresponding to the size of the first bias current and the second bias current minus the current sinked by the current sink 200 Output The principle of the current mirror is obvious to those skilled in the art, and thus detailed description thereof will be omitted.

The output terminal 140 outputs an output current having a magnitude equal to the difference between the current mirrored by the first current mirror and the current mirrored by the second current mirror. That is, since the voltage is input through the differential input unit 110 and then the current is output through the output terminal 140, the transconductance amplifier becomes.

In the operational transconductance amplifier, the first current mirror 120 receives and mirrors a current of I ₄ , which is as small as the current I ₁₀ , which always exits through a current sink 200 among the first bias currents I ₂ . . In addition, the second current mirror 130 receives and mirrors a current of I ₃ having a small size as much as current I ₉ , which always exits by a certain magnitude, through the current sink 200 of the second bias current I ₁ .

The current control technique is used here to be used to increase the voltage gain by obtaining a high output resistance without the need for a cascode output stage. This will be described with reference to the transistor shown in FIG. 2. Here, it is assumed that the first bias current is a positive current and the second bias current is a negative current. Portions of the drain currents I ₁ (positive current) and I ₂ (negative current) of the transistors M1 and M2 flow to the current sink 200 having a predetermined size consisting of the transistors M9 and M10. That is, part of the positive current and negative current are copied (mirror) to the output stage, so that the output resistance component of the operational transconductance amplifier is increased. However, the trans-conductance Gm is the same as the conventional operational transconductance amplifier shown in FIG. 1A. Thus, the overall voltage gain of the operational transconductance amplifier circuit can be increased by the ratio (B + C) / B without loss of output voltage swing.

Here, the alphabet displayed in the lower part of the circuit shown in FIG. 2 represents the size (W / L) of each transistor. Therefore, I ₄ is smaller than I ₂ at a ratio of B / (B + C), and the output resistance is inversely proportional to the drain current I _D of each transistor, and thus increases at a ratio of (B + C) / B, The overall voltage gain is increased by (B + C) / B. For example, if 90% of the drain current of transistor M2 flows into transistor M10 in the standby state, B and C need to be 1: 9 respectively. In this case, the DC gain is increased 10 times.

However, the operational transconductance amplifier in Figure 2 reduces the maximum output current at the same rate. In other words, a higher voltage gain is obtained by reducing the output current. This can be understood if we remember that r _o , the small signal output resistance component of the transistor, is represented by 1 / λ I _D. Where λ and I _D are the channel-length modulation coefficient and the drain current, respectively. If the drain current is reduced, the voltage gain can be increased as described above. However, the operational transconductance amplifier shown in Fig. 2 is consumed without any help in drain current flowing through the current sink 200 consisting of transistors M9 and M10 to raise the maximum output current. Therefore, a circuit for allowing the drain currents of the consumed M9 and M10 to be turned to the output stage to sufficiently increase the maximum output current of the operational transconductance amplifier will be described in detail below.

3 is a circuit diagram of an operational transconductance amplifier using a current sink according to another embodiment of the present invention. Referring to FIG. 3, the operational transconductance amplifier includes a bias unit 100, a differential input unit 110, a first current mirror 120, a second current mirror 130, an output terminal 140, and a current sink 300. It includes.

The bias unit 100 generates a bias current using the bias voltage.

The differential input unit 110 includes a first input terminal and a second input terminal. The first voltage is input through the first input terminal and the second voltage is input through the second input terminal, and the bias current corresponding to the difference between the first voltage and the second voltage is converted into the first bias current and the second bias current. To distribute. Here, some of the first bias current and the second bias current are supplied to the current sink 300 to be described below to generate a sink current.

The current sink 300 includes a first current sink 310 and a second current sink, and since the operation principle is the same, the first current sink 310 will be described below.

The first current sink 310 has a sink voltage of a second voltage, and current sinks a part of the second bias currents by current mirroring. Specifically, the first transistor M11 and the first sink current mirror (including M10 and M13) are formed.

The first transistor M11 receives a first voltage through its gate, a source is connected to a bias part to receive a part of the second bias current, and a drain is a P-type transistor that outputs a part of the received second bias current. The first sink current mirror receives a current output through the drain of the first transistor to mirror the current to generate a sink current. It is connected to a portion where the differential input unit 110 and the first current mirror 120 to be described below are connected, so that a portion of the current input to the first current mirror 120 sinks current.

The first current mirror 120 and the second current mirror 130 respectively output current by mirroring the input current.

The output terminal 140 outputs a current corresponding to the difference between the current mirrored by the first current mirror 120 and the current mirrored by the second current mirror 130.

The operation principle of the operational transconductance amplifier using the current sink shown in FIG. 3 will be described below with reference to the transistor shown in FIG. 3. Here, the alphabet at the bottom of the circuit shown in Fig. 3 represents the size (W / L) of the transistors constituting the circuit.

First, in the standby state, the first voltage and the second voltage coming into the differential input unit 110 are the same. That is, since there is no difference between the first voltage and the second voltage, the first bias current and the second bias current have the same magnitude. Among the transistors M11 constituting the first current sink 310 and the transistors M1 receiving the second voltage among the transistors constituting the differential input unit 110, D: (B + C) is formed according to the ratio of the size (W / L). The second bias current is divided and received in a ratio. Part of the second bias current input to transistor M11 is current mirrored through transistors M13 and M10, and is repeated with the drain current of M10 to become a sink current. Only a part of the first bias current is the drain current of the transistor M2 constituting the differential input unit 110, and the drain current of M10 is sinked out of the first bias current. That is, only current as much as (I ₂ -I ₁₀ ) is input to the first current mirror 120, current mirrored, and repeated at the output terminal.

The same process as described above is repeated through the second current mirror 130, and the output current is zero because the drain currents of M8 and M6 are the same in magnitude through the output terminal 140. However, the standby current at this time is because the bias current is reduced by a certain amount through the current sink 300 is mirrored, power consumption in the standby state is reduced.

In the future, a case where a high output current is required will be described on the assumption that the first voltage is lowered and the second voltage is increased. Since the first voltage is smaller than the second voltage and the transistor constituting the differential input unit 110 is a P-type transistor, the first bias current is larger than the second bias current. That is, the first bias current output through the transistor M2 of the differential input unit 110 has a larger value than in the standby state. A portion of the second bias current input to M11 of the first current sink 310 has a smaller value than in the standby state, which is similarly smaller than in the standby state in the sink current generated through M13 and M10 repeatedly. Will have current. Thus, a higher output current can be obtained compared to the operational transconductance amplifier of FIG. 2 which had a constant sink current.

That is, the operational transconductance amplifier circuit shown in FIG. 3 normally passes a large amount of current through a separate path to prevent excessive current consumption at the output stage, and when a high output current is required, all currents flowing in a separate path at ordinary times are output stages. It is a circuit to supply sufficiently high output current by transferring to the circuit.

만큼 증가한다면 트랜지스터 M10을 통해 흐르는 전류는

만큼 감소하게 된다. 여기서, Vin은 (Vp -Vn) 즉, 제1 전압과 제2 전압의 차이이다. 트랜지스터 M10에서 감소된 전류의 양은 트랜지스터 M4에서 증가된 전류의 여분의 양과 같다. 그러므로 트랜지스터 M4에서의 전체 전류 변화량은 트랜지스터 M2와 M10에서의 변화량의 합이 된다. 여기서, 같은 오버드라이브(overdrive) 전압을 갖기 위해서, 트랜지스터 M1 및 M2는 B+C의 사이즈를 갖고, M11 및 M12는 D의 사이즈를 갖는다고 도 3에 도시된 바와 같이 가정한다. 그렇다면 도 3에 도시된 연산 트랜스컨덕턴스 증폭기의 트랜스컨덕턴스는 수학식 (2)과 같다. Transistors M11 to M14 adjust the drain currents of transistors M9 and M10. For example, the first positive current, which is the current flowing through transistor M2,

Increases by the current flowing through transistor M10

Decrease by. Here, Vin is (Vp-Vn), that is, the difference between the first voltage and the second voltage. The amount of reduced current in transistor M10 is equal to the extra amount of increased current in transistor M4. Therefore, the total amount of change in current in transistor M4 is the sum of the amounts of change in transistors M2 and M10. Here, assume that transistors M1 and M2 have a size of B + C, and that M11 and M12 have a size of D, in order to have the same overdrive voltage, as shown in FIG. Then, the transconductance of the operational transconductance amplifier shown in FIG. 3 is expressed by Equation (2).

- 수학식 (2)

Equation (2)

이기 때문에 다시 쓰게 되면 수학식 (3)과 같이 변하게 된다. here,

Because of this, if you write again, it will change as shown in Equation (3).

- 수학식 (3)

Equation (3)

Since the small signal resistance component at the drain of the transistor M13 or M14 is small, the pole at that point is at a high frequency. Therefore, the poles due to the small signal resistance components of transistors M13 and M14 cannot be dominant poles and thus do not seriously affect the frequency response, so the above equation is ignored. Other important operational transconductance amplifier parameters are summarized in Table 1 as conventional operational transconductance amplifiers and operational transconductance amplifiers according to the present invention.

TABLE 1

Original OTA OTA according to the present invention Transconductance Gm

Output Resistance Ro

Standby Output Current Quiescent output current Io, Q

Max output current Io, max

The operational transconductance amplifier according to the present invention shows better performance at Gm, output resistance component and standby output current. However, the maximum output current may appear to be slightly worse than the operational transconductance amplifier of the operational transconductance amplifier according to the present invention.

For a fair performance comparison, the following two points are discussed. First, the transconductances gm1,2 of the two operational transconductance amplifiers in Table 1 are different values. The reason is that in the operational transconductance amplifier shown in FIG. 3, the first bias current is dividedly input according to the ratio (W / L) of the transistors M2 and M12. Since M2 is (B + C) and M12 is D, gm1,2 of the operational transconductance amplifier according to the present invention is (B + C) / (B + C) than gm1,2 of the conventional operational transconductance amplifier. As small as + D).

Second, the maximum output current of the operational transconductance amplifier according to the present invention is not worse than the maximum output current of the conventional operational transconductance amplifier. If the operational transconductance amplifier according to the present invention and the conventional operational transconductance amplifier are designed to have the same quiescent current, the operational transconductance amplifier according to the present invention will have a higher slew rate, which shows excellent performance.

As another embodiment according to the present invention, it is assumed that both the conventional operational transconductance amplifier and the operational transconductance amplifier according to the present invention have a bias current of 200 μA. In contrast, quiescent currents are 400μA and 40μA, respectively. In the conventional operational transconductance amplifier, the value of A: B is 4: 1, but the value of A: B: C: D of the operational transconductance amplifier according to the present invention is 4: 1: 1: 8: 1. It can be seen that in the operational transconductance amplifier according to the present invention, the standby output current is significantly reduced, and only the maximum output current is slightly smaller than the conventional operational transconductance amplifier. As described above, if a higher slew rate is desired, the A value or the bias current of the operational transconductance amplifier according to the present invention can be increased. In other words, when the two operational transconductance amplifiers have the same magnitude of quiescent current, the slew rate of the operational transconductance amplifier according to the present invention is much higher than that of the conventional operational transconductance amplifier.

4 is a frequency response result diagram using a conventional operational transconductance amplifier, Figure 5 is a frequency response result diagram using an operational transconductance amplifier according to the present invention. Here, the HSPICE simulation results use 0.35μm CMOS processor parameters. When the load capacitor of 10pF is attached to the output terminal 140 and simulated, it is a frequency response of the conventional operational transconductance amplifier and the operational transconductance amplifier according to the present invention.

4 to 5, the DC gain of the operational transconductance amplifier according to the present invention is much higher than the conventional operational transconductance amplifier having 40dB (= 20log100) at 62dB (# 20log1000). In addition, the unity-gain frequency of the conventional operational transconductance amplifier is 43MHz, the phase margin is 81 °. On the other hand, the operational transconductance amplifier according to the present invention has a unity gain frequency of 46 MHz, and the phase margin is 64 °. The addition of transistors affects the non-dominant poles, reducing the phase margin of the operational transconductance amplifier according to the invention, but still having sufficient phase margin.

The operational transconductance amplifier presented in the present invention obtains a high DC gain by regulating the output current instead of using the cascode method at the output stage. The output stage uses a class AB circuit, resulting in low quiescent current and high output resistance. On the other hand, the output current increases as required. The new operational transconductance amplifier can be used for low voltage and high speed switch-capacitor circuits.

The present invention is not limited to the above embodiments, and many variations are possible by those skilled in the art within the spirit of the present invention. In addition, the scope of the present invention can be interpreted only by the claims described below.

As described above, the operational transconductance amplifier using the current sink according to the present invention has a frequency compensation to obtain a high DC voltage gain with good dominant pole characteristics and a small standby current.

In addition, the operational transconductance amplifier using the current sink according to the present invention has good power efficiency and can be used in switch-capacitor circuits requiring low voltage and high speed due to high DC voltage gain and high power efficiency.

In addition, portable battery-powered devices can be an essential factor in maximizing the performance of a system with a low voltage in many modern times.

Claims (9)

In operational transconductance amplifiers, A bias unit generating a bias current using the bias voltage; A first bias current including a first input terminal and a second input terminal, the bias current corresponding to a difference between a first differential voltage and a second differential voltage received through the first input terminal and the second input terminal; And a differential input unit configured to distribute the second bias current; A first current sink and a second current sink connected to the differential input to sink some of the first bias current and the second bias current; A first current mirror configured to mirror the current by receiving a current corresponding to a difference between the first bias current and the current sinked by the first current sink; A second current mirror configured to mirror the current by receiving a current corresponding to a difference between the second bias current and the current sinked by the second current sink; And An output terminal for outputting a current corresponding to a difference between the current mirrored by the first current mirror and the current mirrored by the second current mirror Operational transconductance amplifier using a current sink comprising a. The method of claim 1, And the first current sink and the second current sink generate a predetermined sink current by a predetermined same sink voltage. The method of claim 2, Each of the first current sink and the second current sink has a drain connected to a connection portion of the differential input portion and the first current mirror, and a connection portion of the differential input portion and the second current mirror, respectively, and through the gate, the sink voltage. Receiving an input, the source of the operational transconductance amplifier using a current sink, characterized in that consisting of a transistor connected to the ground. The method of claim 1, The first current sink and the second current sink is an operational transconductance amplifier using a current sink, characterized in that for generating a sink current of a different size by different sink voltages other than the standby state. The method of claim 4, wherein the first current sink is And the sink voltage is the second voltage, and a current sink is performed by current mirroring a part of the second bias currents. The method of claim 5, wherein the first current sink, A first transistor having a gate input to the second voltage, a source connected to the bias unit, and a drain of which outputs a part of the second bias current; And And a first sink current mirror configured to receive the current output through the drain of the first transistor and mirror the current to generate the sink current. The method of claim 5, wherein the second current sink is And the sink voltage is the first voltage, and a current sink is performed by current mirroring a part of the first bias current. The method of claim 7, wherein the second current sink, A second transistor having a gate input to the first voltage, a source connected to the bias unit, and a drain outputting a part of the first bias current; And And a second sink current mirror configured to receive the current output through the drain of the second transistor and mirror the current to generate the sink current. The method according to any one of claims 3, 6 and 8, The transistor included in the operational transconductance amplifier is an operational transconductance amplifier using a current sink, characterized in that the CMOS.

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