A signal amplifier includes a first amplifier, a second amplifier, and an output. The first amplifier amplifies a first input signal to form a first amplified output signal. The first input signal has a common mode voltage in a first voltage range, and the first amplified output signal has a common mode voltage in a second voltage range different from the first voltage range. The second amplifier amplifies a second input signal to form a second amplified output signal. The first input signal has the common mode voltage in the second voltage range and the second amplified output signal has the common mode voltage in the second voltage range. The output outputs the first amplified output signal or the second amplified output signal as an amplified output signal.
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