| 摘要 |
A programmable gain amplifier having three separately programmable amplifiers. A programmable transconductance amplifier is followed by a programmable transimpedance amplifier, then a programmable switched capacitor amplifier. In one embodiment, this programmable gain amplifier is implemented in an analog front-end (AFE) circuit. One AFE embodiment provides a coarse pre-gain offset a black reference level sampler, and a fine post-gain offset in the programmable switched capacitor amplifier. In one embodiment, an ADC reference is sampled, and is subtracted directly from the video signal in the switched capacitor amplifier so that the zero level of the video signal is made to correspond to the zero level of the ADC. In another embodiment, a piece-wise linear approximation of an exponential gain function is implemented by programming the transconductance and transimpedance amplifiers to provide exponential jumps in gain, while the switched capacitor amplifier is programmed to interpolate as needed between the exponential gain levels.
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