Two-stage fully-differential low-noise low-offset chopping operational amplifier

Abstract

The invention relates to the technical field of design of complementary metal oxide semiconductor transistor (CMOS) operational amplifiers and in particular discloses a two-stage fully-differential low-noise low-offset chopping operational amplifier, which comprises choppers S1, S2 and S3 and a two-stage folded cascade operational amplifier, wherein the chopper S1 modulates an input signal to a chopping frequency; the two-stage folded cascade operational amplifier amplifies the signal which is modulated by the chopper S1; the chopper S2 demodulates the signal to a base band; and the chopper S3 is used for dynamically switching a differential pair tube of a current source in the amplifier, so that the current mismatching of the current source and an offset voltage of the amplifier are further reduced. An output offset voltage and an equivalent input noise of the operational amplifier are effectively reduced, output amplitude is improved, a capacitor of an output end and operational amplification output impedance form a low-pass filter, an additional low-pass filter is not required to be designed, and the two-stage fully-differential low-noise low-offset chopping operational amplifier is quite applicable to a sensor detection circuit.

Description

technical field [0001] The invention relates to the technical field of CMOS operational amplifier design, in particular to a two-stage fully differential low-noise and low-offset chopper operational amplifier suitable for sensor detection circuits. Background technique [0002] Modern CMOS integrated circuit technology is developing rapidly towards deep submicron, which makes analog signal processing circuits need to face the reduction of power supply voltage and the impact of 1 / f noise and offset voltage. At the same time, sensor technology is developing towards miniaturization and integration, and will eventually realize the single-chip integration of sensors and sensor detection circuits. However, the sensor signal is basically in the low-frequency band, and the signal amplitude is small. The offset of the back-end CMOS detection circuit and low-frequency 1 / f noise become the most important factors restricting the single-chip integration of the sensor and the detection ci...

AI Technical Summary

Problems solved by technology

[0004] A conventional single-stage chopper op amp structure such as figure 1 As shown, the chopper is located at the input and output high-impedance nodes of the operational amplifier. On the one hand, the switching noise of the modulation switch is directly coupled to the output terminal, which introduces a large amount of switching noise residue, resulting in a low chopping frequency, generally within tens of kHz. Limits the bandwidth of useful signals

On the other hand, in low-voltage applications, when modulating large-amplitude signals, it is necessary to add a charge pump to make the chopper turn off stably, and a low-pass filter needs to be added in the subsequent stage to filter out the modulation to high-frequency offset and 1 / f noise, and then through a single-ended to differential circuit, it can be connected to the analog-to-digital converter, and the circuit structure is complex

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