Method for compensating frequency of wideband common mode feedback loop of two-stage operational amplifier

An operational amplifier and common-mode feedback technology, applied in the direction of differential amplifiers, DC-coupled DC amplifiers, etc., can solve the problems of increasing circuit manufacturing costs and power consumption, and achieve the effects of simple circuit design, low power consumption, and fewer components

Inactive Publication Date: 2009-01-28
RESEARCH INSTITUTE OF TSINGHUA UNIVERSITY IN SHENZHEN
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  • Abstract
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Problems solved by technology

like image 3 The two-stage operational amplifier requires two common-mode feedback loops, which increases the manufacturing cost and power consumption of the circuit

Method used

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  • Method for compensating frequency of wideband common mode feedback loop of two-stage operational amplifier
  • Method for compensating frequency of wideband common mode feedback loop of two-stage operational amplifier
  • Method for compensating frequency of wideband common mode feedback loop of two-stage operational amplifier

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Embodiment Construction

[0014] The present invention will be described below in conjunction with the accompanying drawings.

[0015] Figure 4 , let the open-loop transfer function of the operational amplifier be H 1 (s)=v out (s) / v in (s), the unity gain bandwidth is UGB 1 , the phase margin is PM 1 ; The transfer function of the operational amplifier in the common-mode feedback loop is H 2 (s)=v out (s) / v cmfb (s), the unity gain bandwidth is UGB 2 , the phase margin is PM 2 ; The transfer function of the broadband feedback amplifier is F(s)=v cmfb (s) / v out (s); then the overall transfer function of the common mode feedback loop is CML(s)=H 2 (s)F(s), the unity gain bandwidth is UGB 3 , the phase margin is PM 3 .

[0016] With proper design, H 1 UGB(s) 1 and H 2 UGB(s) 2 Meet UGB 1 ≈UGB 2 , PM 1 ≈PM 2 . Since the dominant pole frequency of the broadband feedback amplifier is much higher than the UGB 1 and UGB 2 , so the dominant pole of the broadband feedback amplifier has...

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Abstract

The invention discloses a method for compensating the frequency of a broadband common mode feedback ring circuit for a two-stage operational amplifier, belonging to the field of analog integrated circuit design. A broadband feedback amplifier in the two-stage operational amplifier with the Miller compensation is used as the common mode feedback ring circuit so as to reduce the area and the power consumption of the common mode feedback circuit; the two-stage operational amplifier has only one main pole in the range of the unit gain bandwidth, a fully differential input and output structure is adopted, the sampling of the common mode output level is performed by the differential output end; and a control signal fed back by the common mode simultaneously controls the output level of a first-stage common mode and the output level of a second-stage common mode of the operational amplifier through a controllable bias circuit. The frequency of the main pole of the broadband feedback amplifier is far higher than the unit gain bandwidth of the operational amplifier, therefore the margin of phase position of the common mode ring circuit is basically equal to that of the operational amplifier, thereby forming the stable feedback ring circuit. The method has the advantages of few elements for a common mode feedback circuit, lower power consumption of the common mode feedback circuit and simpler and more convenient circuit design.

Description

technical field [0001] The invention belongs to the field of analog integrated circuit design, in particular to a frequency compensation method for a broadband common-mode feedback loop of a two-stage operational amplifier. Background technique [0002] Integrated amplifiers generally adopt 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] An integrated operational amplifier is a commonly used circuit unit. In order to achieve high gain and large output signal range, a two-stage structure is generally used. In order to ensure that the feedback circuit formed by the...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H03F3/45
Inventor 王自强张春王志华
Owner RESEARCH INSTITUTE OF TSINGHUA UNIVERSITY IN SHENZHEN
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