| 摘要 |
A programmable gain amplifier includes an operational amplifier coupled thereto a plurality of resistors to perform a feedback control, thereby rendering a closed-loop gain <maths id="MATH-US-00001" num="00001"> <math overflow="scroll"> <mrow> <mrow> <mrow> <msub> <mi>A</mi> <mi>f</mi> </msub> <mo></mo> <mrow> <mo>(</mo> <mi>s</mi> <mo>)</mo> </mrow> </mrow> <mo>=</mo> <mfrac> <mrow> <mi>A</mi> <mo></mo> <mrow> <mo>(</mo> <mi>s</mi> <mo>)</mo> </mrow> </mrow> <mrow> <mn>1</mn> <mo>+</mo> <mrow> <mrow> <mi>A</mi> <mo></mo> <mrow> <mo>(</mo> <mi>s</mi> <mo>)</mo> </mrow> </mrow> <mo>.</mo> <mi>beta</mi> </mrow> </mrow> </mfrac> </mrow> <mo>,</mo> </mrow> </math> </maths> where beta is a feedback factor determined by the resistance of the resistors and A(s) is an open-loop gain of the operational amplifier. The operational amplifier includes a first-stage amplifying circuit, a second-stage amplifying circuit, and a compensating capacitor coupled to an output end of the first-stage amplifying circuit and having an equivalent capacitance variable to adjust a dominant-pole frequency of the open-loop gain of the operational amplifier.
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