CMOS buffer circuit for driving high capacitive load

Abstract

The invention discloses a CMOS buffer circuit for driving a high capacitive load. The CMOS buffer circuit is mainly applied to a high precision signal processing system and comprises a first stage operational amplifier, a voltage-controlled current source and a second stage operational amplifier. The forward direction input end of the first stage operational amplifier is connected with input signals, the output end of the first stage operational amplifier is connected with the output end of the voltage-controlled current source and the input end of the second stage operational amplifier, and the output end of the second stage operational amplifier is connected with the reverse direction input end of the first stage operational amplifier. The CMOS buffer circuit for driving the high capacitive load has the advantages of being simple in circuit structure, high in performance, capable of driving the high capacitive load, low in cost and easy to popularize in a wide range.

Description

technical field [0001] The invention relates to a CMOS buffer circuit, in particular to a high-precision signal processing system, and belongs to the field of integrated circuits. technical background [0002] As a common circuit unit in integrated circuits, buffers are widely used in various analog systems and hybrid systems. The buffer is formed by short-circuiting the inverting input terminal of an operational amplifier and its output terminal, and is used in the circuit system for impedance transformation and improving the driving capability of the previous stage circuit. The two most important characteristics of the buffer, one is the loop gain of the buffer, which determines the accuracy of the buffer; the other is the stability of the buffer loop, generally speaking, there is a trade-off relationship between these two characteristics. In some applications, the buffer needs to drive a large capacitor, such as 100pF. At this time, the buffer is required to have a large...

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Problems solved by technology

And when the load capacitance at the output end of the buffer is much larger than the Miller capacitance, the pole at the output end of the buffer will be in the low frequency region, and when the distance between the main pole and the pole at the output end is too close, the loop stability of the buffer is difficult to guarantee, so Buffers using this op amp cannot drive large capacitors

In addition, if the main body of the buffer adopts a single-stage operational amplifier, such as a folded cascode amplifier, when using it to drive a large capacitor, the loop stability of the buffer can be guaranteed, but its loop gain is only about 60dB, which is high at high Not suitable for precision applications

In addition, there are other operational amplifier structures that can form a high loop gain and drive a buffer with a large load capacitance, but the general structure is complex and the application is inconvenient

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