Large-bandwidth continuous time common-mode feedback circuit and design method thereof

Abstract

The invention relates to a large-bandwidth continuous-time common-mode feedback circuit and a design method thereof. The method comprises the following steps of: designing an ideal common-mode signal; detecting the common-mode value of an operational amplification output signal through a common-mode detection circuit; comparing the detected common-mode value of the operational amplification output signal with that of the ideal common-mode signal; after amplifying an error signal through the common-mode feedback circuit, outputting two common-mode feedback control signals fed back to the drain electrode of a biasing tube of an operational amplification biasing circuit so that the whole common-mode feedback circuit forms a single-stage amplifier to ensure that the common-mode feedback circuit has enough phase margin; and finally stabilizing the operational-amplified output common-mode point on the ideal common-mode value according to the negative feedback function of common-mode feedback. The invention overcomes the defects that the traditional continuous-time common-mode feedback circuit is a multi-stage amplifier and has poor stability, and ensures that the common-mode feedback circuit is a one-stage common-source cathode-input amplifier through adjusting the feedback point of the common-mode feedback; and the common-mode feedback circuit has favorable stability and is suitable for large-bandwidth ultrahigh-speed full-differential analog circuits.

Description

technical field [0001] The invention relates to a common mode feedback circuit. In particular, it relates to a design method and circuit of a large-bandwidth continuous-time common-mode feedback circuit with first to tenth bias tubes, which is applied to a fully differential operational amplifier to meet the high bandwidth and stability requirements of the operational amplifier. Background technique [0002] The fully differential circuit has become a common circuit form due to its high output swing and the suppression of common-mode noise such as power supplies. The key and difficult point of the fully differential circuit design is the design of the common-mode feedback circuit, and the common-mode feedback circuit is a fully differential operational amplifier. In high-gain amplifiers, the output common-mode level is quite sensitive to device characteristics and mismatches, and cannot be stabilized by differential feedback. Therefore, a common-mode feedback network must b...

AI Technical Summary

Problems solved by technology

Usually, the error amplifier is a one-stage common-source amplification structure, so that the common-mode feedback loop adds at least one more common-source amplification. For the application requirements of large bandwidth, it is difficult for the common-mode feedback loop to meet the application requirements of sufficient phase margin.

[0010] like image 3 As shown, in the traditional continuous-time common-mode feedback, the feedback point of the common-mode feedback is connected to the gate of the bias tube in the op amp. For a fully differential operational amplifier with a traditional common-mode feedback circuit, the circuit is as follows Figure 4 shown, in this case, from the input V cmfb And Vcm to the output terminals Voutn and Voutp of the operational amplifier, which is equivalent to adding a folded cascode amplifier and a common source amplifier on the basis of the common-mode feedback common-source amplifier. For large-bandwidth operational amplifiers, the common-mode The phase margin of the feedback circuit will be difficult to meet

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