CN104765399A - CMOS low-temperature small-noise operation amplifying circuit - Google Patents

Abstract

The invention discloses a CMOS low-temperature and low-noise operational amplifier circuit. The bias circuit part adopts the method of multi-stage current mirror sleeve structure, and the reference current reference is generated by using two diode-connected MOS tube active resistances, so that the reference current of the amplifier It has good temperature characteristics; the amplification part adopts a folded cascode structure with differential input, and the open-loop gain of the amplifier can be greater than 80dB when the first-stage amplification is used, which overcomes the Miller compensation capacitor used in the traditional second-stage amplification at a low temperature of 77K The shortcoming that it is easy to cause oscillation; the differential input pair tube adopts a large tube with a width-to-length ratio greater than 100, which is conducive to improving the noise performance of the CMOS amplifier. The differential operational amplifier can work normally between room temperature and low temperature 77K, and can be used as a low-temperature CMOS The standard amplifier module of the circuit design is used, which can be applied not only in the photovoltaic infrared detector circuit, but also in the long-wave infrared photoconductive detector circuit.

Description

CMOS Low Temperature Low Noise Operational Amplifier Circuit

technical field

The invention relates to a CMOS operational amplifier circuit, in particular to a CMOS low-temperature and low-noise operational amplifier circuit.

Background technique

In the field of aerospace remote sensing, most infrared detectors work at low temperature. In order to improve the performance of the system and reduce the interference introduced by the outside world, it is required that the detector be connected to the circuit in close proximity, that is, the designed circuit also needs to work at low temperature. Currently, commercialized circuit products are designed for room temperature and may not work properly at low temperatures. In order to improve the performance of the system, it is necessary to design a CMOS readout circuit that can work normally at low temperature. The core module in the readout circuit is a CMOS differential operational amplifier. If there is a mature low-temperature CMOS differential operational amplifier module, it will be more beneficial to the low temperature in the future. CMOS circuit design.

The Chinese patent CN 1588794A of Cao Bisong et al., authorized on March 2, 2005, announced a low-temperature low-noise amplifier in the radio frequency band. The amplifier belongs to the field of radio frequency technology and is mainly used in the CDMA band. , without using the current conventional CMOS process, it cannot be applied to the design of the current mainstream CMOS circuits.

Contents of the invention

The purpose of the present invention is to provide a CMOS differential operational amplifier standard module that can be applied in low-temperature CMOS circuit design, so as to improve the design level of low-temperature CMOS application-specific integrated circuits. The amplified part of the low-temperature CMOS differential operational amplifier is shown in Figure 1, which includes an amplifying circuit module and a biasing circuit module, wherein:

The amplifying circuit module adopts an amplifying circuit of a folded cascode structure with differential input, wherein the differential input pair tube adopts a PMOS tube with a width-to-length ratio equal to 100;

The differential input in the amplifying circuit module is composed of two PMOS tubes with a width-to-length ratio of 1500 μm/1.5 μm, and 72 41.7 μm/1.5 μm tubes are used to form the input pair PM7 and PM8, and interdigitated transistors are used to ensure the up and down and Left and right symmetrical, and a protective ring is used outside the input pair tube;

In the described amplifying circuit module, PM7, PM8, NM4, NM5 form the cascode structure of differential input, PM4, PM5 are the active loads of differential output, NM6, NM7 provide current source for cascode, Bias1, Bias2 and Bias3 are bias voltage ports, the voltage of which is supplied by the bias circuit module, and In- and In+ are the positive and negative input terminals of the differential operational amplifier;

The bias circuit module adopts a multi-level current mirror construction method, and its reference current part is composed of active resistors connected by diodes; the bias circuit is composed of eight tubes, and NM3 and NM0 form the first stage current PM0 and PM1 form a second-stage current mirror, NM1 and NM6 and NM7 of the enlarged part form a current mirror, PM0 and PM3 of the enlarged part form a current mirror; PM2 and NM3 connected by diodes form a reference current source, and NM3 Mirrored to NM0 to generate one current, and then mirrored from PM0 to PM1 to generate another current.

In the first-stage folded cascode structure with differential input, PM7 and PM8 are input pair tubes, PM7, PM8, NM4, and NM5 form a cascode structure with differential input, PM4, PM5 are active loads for differential output, and NM6 , NM7 provides a current source for the cascode, Bias1, Bias2, Bias3 are bias voltages, In-, In+ are the positive and negative input terminals of the differential operational amplifier. The bias circuit part of the low-temperature CMOS differential operational amplifier is shown in Figure 2, where NM3 and NM0 constitute the first-stage current mirror, PM0 and PM1 constitute the second-stage current mirror, and NM1 and NM6 and NM7 of the amplification part constitute the current mirror. PM0 and PM3 of the enlarged part form a current mirror.

The input tube of this CMOS low-temperature low-noise differential operational amplifier adopts a large tube of 1500μm/1.5μm, which greatly reduces the equivalent input noise of the amplifier; the circuit topology adopts a one-stage folded cascode structure, without using Miller compensation capacitors, It overcomes the shortcoming of ordinary two-stage amplifiers that easily cause circuit oscillation due to the change of Miller compensation capacitance at low temperature; the bias circuit of the low-temperature amplifier adopts a three-stage mirror image method, and does not use polysilicon resistors to generate reference currents, which overcomes polysilicon resistors. Disadvantages of temperature changes causing the static operating point of the circuit to drift. This CMOS differential operational amplifier can work well between room temperature and low temperature 77K. This design method is suitable for most micron or submicron microelectronic processes. The operational amplifier can be used as a standard amplifier module designed for CMOS circuits, which can be applied to photovoltaic infrared detector circuits and long-wave photoconductive infrared detector circuits.

The advantages of the present invention are as follows:

1. The CMOS low-temperature and low-noise operational amplifier module uses a cascode structure, and the amplification factor of more than 80dB can be achieved in one stage of amplification. The power supply voltage rejection ratio is also relatively high, which reduces the noise introduced by power supply ripple.

2. When the CMOS low-temperature and low-noise operational amplifier module is used in an infrared photovoltaic detector circuit, its equivalent input current noise is less than 0.03pA/Hz ^1/2 1KHz.

3. The CMOS low-temperature low-noise operational amplifier module can work normally from room temperature 300K to low temperature 77K. It can not only be applied to the signal amplification of photovoltaic and photoconductive infrared detectors, but also can be used as a standard operational amplifier module for other low-temperature CMOS circuits.

4. The CMOS low-temperature and low-noise operational amplifier module is manufactured by standard micron or submicron CMOS technology, which ensures the repeatability of chip manufacturing.

5. The CMOS low-temperature and low-noise operational amplifier module does not need to use compensation capacitors, which overcomes the disadvantage that the compensation capacitors of ordinary two-stage amplifiers change at low temperatures and easily cause circuit oscillation.

Description of drawings

Figure 1 is a partial structural diagram of the amplifier circuit of the CMOS low-temperature and low-noise operational amplifier module.

Figure 2 is a partial structure diagram of the bias circuit of the CMOS low-temperature and low-noise operational amplifier module.

Figure 3 is a symmetrical layout of the input pair tube of the CMOS low-temperature and low-noise operational amplifier module.

Figure 4 is a simulation result graph of the open-loop gain of a CMOS low-temperature and low-noise op amp.

Figure 5 is a general diagram of the amplifying circuit of the CMOS low-temperature and low-noise operational amplifier module.

Detailed ways

The specific embodiment of the present invention is described in further detail below in conjunction with accompanying drawing:

Example 1

The total noise of this circuit is mainly determined by the input tubes PM7 and PM8, and the equivalent input noise voltage calculation formula is:

$S_{v_e}\left(f\right)=\frac{8}{3}\frac{\mathrm{kT}}{g_m}+\frac{K_f}{C_{\mathrm{ox}}^2\mathrm{WL}}\frac{1}{f}$ (in $g_m=\sqrt{{2K}_p\frac{W}{L}{I}_{\mathrm{ds}}}$ )

The first term is channel thermal noise and the second term is 1/f noise.

g _m is the transconductance of the input tube. In order to reduce the total noise, the size of the input tube W/L and the design of the bias current are very important. It can be seen from the above formula that increasing g _m can reduce channel thermal noise. Under the condition of area permitting, increase the W/L of the input tube, use 1500μm/1.5μm to increase g _m , and use 72 when drawing the layout The 41.7μm/1.5μm tubes form the input pair tubes PM7 and PM8, and a protective ring is used outside the input pair tubes, which is beneficial to reduce the input pair tube imbalance and external crosstalk noise. The 1/f noise of PMOS is smaller than that of NMOS, so the input tubes PM7 and PM8 choose PMOS to reduce the 1/f noise. In addition, increasing W×L can also reduce 1/f noise. Under the conditions of power consumption and area permitting, other tubes should also be designed with low noise standards in mind as much as possible. When the temperature decreases, the increase of the current and the increase of the threshold voltage V _T may make the device unable to work, so it must be fully considered when designing the W/L of each tube.

The amplified part of the low-temperature low-noise CMOS differential operational amplifier is shown in Figure 1, which adopts a one-stage folded cascode structure with differential input. Among them, PM7 and PM8 are input pair tubes, PM7, PM8, NM4, and NM5 form a cascode structure of differential input, PM4, PM5 are active loads of differential output, NM6, NM7 provide current source for cascode, Bias1 , Bias2, Bias3 are bias voltages, In-, In+ are the positive and negative input terminals of the differential operational amplifier. The tube reference size of the enlarged part is shown in the table below (in microns).

tube PM7, PM8 NM4, NM5 NM6, NM7 PM4, PM5 PM3 W/L 1500/1.5 120/10 120/10 10/10 200/10

Example 2

The bias circuit part of this low-temperature low-noise CMOS differential operational amplifier is shown in Figure 2, where NM3 and NM0 constitute the first-stage current mirror, PM0 and PM1 constitute the second-stage current mirror, and NM1 and NM6 and NM7 of the amplifying part constitute the current mirror. Mirror, PM0 and PM3 of the enlarged part constitute a current mirror.

The bias part is composed of eight tubes. PM2 and NM3 connected by diodes form a reference current source. NM3 is mirrored to NM0 to generate one current, and then PM0 is mirrored to PM1 to generate another current. This current source does not use the pair Passive resistors that are particularly sensitive to temperature, so the current source can work normally at room temperature and low temperature. The test results show that the current source has a strong temperature suppression ability, so the entire low-temperature CMOS differential operational amplifier chip has a wide operating temperature range, from room temperature to It can work normally from 300K to low temperature 77K.

The tube reference size of the bias circuit part is shown in the table below (unit is micron).

tube PM1, PM0, NM1 NM0, NM3, PM2 NM2 PM6 W/L 10/10 10/50 100/10 40/10

Example 3

When drawing the layout of the amplifier, all pairs of tubes use interdigitated transistors, and try to ensure up-down and left-right symmetry, which can reduce the input offset of the CMOS differential operational amplifier at low temperature, especially the input tube of the differential amplifier, which is particularly important. In this circuit, since the differential input pair tube uses a large tube of 1500μm/1.5μm, in order to achieve up-down and left-right symmetry, 72 41.7μm/1.5μm tubes are used to form the input pair tube when drawing the layout, as shown in Figure 3 It is shown that this greatly reduces the input offset of the entire differential operational amplifier, and the test results show that the input offset voltage of the low-temperature low-noise CMOS differential operational amplifier is very small, less than 1mV.

Example 4

The low-temperature and low-noise CMOS differential operational amplifier module adopts a folded cascode structure with differential input. The open-loop gain of the first-stage amplification exceeds 80dB, reaching the amplification factor of the conventional two-stage amplification. The gain simulation of the differential operational amplifier The result is shown in Fig. 4, and its open-loop gain reaches 88dB. Conventional amplifiers use two-stage amplification and need to use Miller compensation capacitors to increase the phase margin. However, at low temperatures, changes in the phase margin may cause amplifier oscillations due to changes in Miller compensation capacitors, so conventional amplifiers are prone to oscillation at low temperatures. . The low-temperature and low-noise CMOS operational amplifier of the present invention adopts one-stage amplification without using a Miller compensation circuit, and this structure overcomes the shortcoming that conventional two-stage amplifiers easily cause oscillation at low temperature. Figure 5 is a general diagram of the CMOS low-temperature and low-noise operational amplifier circuit. Bias1, Bias2, and Bias3 in the bias circuit part are connected to Bias1, Bias2, and Bias3 in the amplifier circuit part. In+ and In- are the positive and negative terminals of the operational amplifier circuit. input terminal.

The CMOS low-temperature and low-noise operational amplifier circuit can be used as an operational amplifier module in the photovoltaic infrared detector CMOS circuit and the photoconductive infrared detector CMOS circuit. After testing, the CMOS low-temperature and low-noise operational amplifier module is equivalent to the infrared photovoltaic detector circuit. The effective input current noise is very low, less than 0.03pA/HZ ^1/2 1KHz.

Since the low-temperature and low-noise CMOS differential operational amplifier adopts a folded cascode structure, the operating voltage range is large, and it can work normally between ±2.5 volts and ±1.2 volts, but it is necessary to consider that the difference in operating voltage causes the unit power consumption is different.

The present invention has been described above through specific examples, but the present invention is not limited to these specific examples. Those skilled in the art should understand that various modifications, equivalent replacements, changes, etc. can also be made to the present invention. As long as these changes do not deviate from the spirit of the present invention, they should all be within the protection scope of the present invention.

Claims (1)

1. A CMOS low-temperature low-noise operational amplifier circuit, comprising an amplifier circuit module and a bias circuit module, is characterized in that: The amplifying circuit module adopts an amplifying circuit of a folded cascode structure with differential input, wherein the differential input pair tube adopts a PMOS tube with a width-to-length ratio equal to 100; The differential input in the amplifying circuit module is composed of two PMOS tubes with a width-to-length ratio of 1500 μm/1.5 μm, and 72 41.7 μm/1.5 μm tubes are used to form the input pair PM7 and PM8, and interdigitated transistors are used to ensure the up and down and Left and right symmetrical, and a protective ring is used outside the input pair tube; In the described amplifying circuit module, PM7, PM8, NM4, NM5 form the cascode structure of differential input, PM4, PM5 are the active loads of differential output, NM6, NM7 provide current source for cascode, Bias1, Bias2 and Bias3 are bias voltage ports, the voltage of which is supplied by the bias circuit module, and In- and In+ are the positive and negative input terminals of the differential operational amplifier; The bias circuit module adopts a multi-level current mirror construction method, and its reference current part is composed of active resistors connected by diodes; the bias circuit is composed of eight tubes, and NM3 and NM0 form the first stage current PM0 and PM1 form a second-stage current mirror, NM1 and NM6 and NM7 of the enlarged part form a current mirror, PM0 and PM3 of the enlarged part form a current mirror; PM2 and NM3 connected by diodes form a reference current source, and NM3 Mirrored to NM0 to generate one current, and then mirrored from PM0 to PM1 to generate another current.