| 摘要 |
A programmable gain amplifier (10) has a differential input (12-13), a differential output (16-17), and a plurality of enable inputs (21, 31-34). The amplifier includes a plurality of transconductor sections (26-29), which each have input nodes coupled to the differential input, output nodes coupled to the differential output, and an enable node coupled to a respective enable signal. The transconductor sections have different gains, which are respective powers of two. Each transconductor section includes a transconductor circuit (51, 56) which is coupled in series with at least one current mirror circuit (52-53, 57-58). Each transconductor circuit has a transistor (121) with a class A quiescent current that is proportional to the corresponding gain, the transistor being sized to achieve an optimum current density for its quiescent current. Each such transistor has two terminals coupled to other circuitry within the transconductor circuit, and a third terminal coupled only to the associated current mirror circuit.
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