Method for compensating common mode feedback circuit frequency of two-stage amplifier

Abstract

The invention discloses a common-mode feedback circuit frequency compensation method of a dual-stage amplifier, which belongs to the analog integrated circuit design field. One common-mode feedback circuit is adopted in the dual-stage amplifier to reduce the area and the power consumption of the feedback circuit; the dual-stage amplifier adopts a fully-differential input / output structure; a differential output terminal is used for sampling the common-mode output level; a first-stage amplifying circuit thereof comprises a controllable biasing circuit; a common-mode feedback control signal controls the first-stage common-mode output level and the second-stage common-mode output level of the amplifier at the same time through the controllable biasing circuit; a feedback amplifier is realizedby adopting a dual-stage operational amplifier with miller compensation. The left half plane zero point generated by the feedback amplifier in a loop circuit counteracts a certain left half plane pole in a prime amplifier, thereby forming a stable compensation loop circuit. The common-mode feedback circuit frequency compensation method has the advantages of less feedback circuit elements, lower feedback circuit power consumption, high low-frequency loop gain and better compensation phase margin.

Description

technical field [0001] The invention belongs to the field of analog integrated circuit design, in particular to a frequency compensation method for a common-mode feedback circuit of a two-stage amplifier. Background technique [0002] Current integrated amplifier designs generally use a fully differential structure, which can suppress common-mode interference and noise. However, the common-mode output level of the differential amplifier will deviate from the design value due to factors such as manufacturing process, operating voltage, and temperature. Therefore, a common-mode feedback circuit is required to determine the output DC level. The stability of the loop needs to be considered when designing a common-mode feedback circuit. [0003] For a two-stage amplifier, the output nodes of the first and second stages correspond to a dominant pole respectively. These two output nodes are called "high-impedance" nodes, and their DC levels are easily affected and deviate from the...

AI Technical Summary

Problems solved by technology

If the low-frequency gain of the common-mode feedback circuit is increased, the feedback amplifier is required to have a high gain. Under a certain power consumption, the bandwidth of the feedback amplifier is small, and the phase margin of the common-mode feedback circuit is further reduced; if the phase margin of the common-mode feedback circuit is increased If the degree is high, the feedback amplifier is required to have a large bandwidth. Under a certain power consumption, its gain decreases, and the low-frequency gain of the common-mode feedback circuit also decreases, and the ability of the loop to stabilize the common-mode output level becomes worse.

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