When an analog signal requires amplification before reaching an ADC, the amplifier's inherent noise can degrade the ADC's output SNR. A compact rule quantifies the maximum allowable amplifier input-referred noise power: it must be less than (1 - 1/α²) times the ADC's quantization noise power (q²/12), where α is the voltage gain. For example, at α=2, the amplifier noise power must stay below 75% of the ADC's quantization noise power. A figure plotting this relationship across gain values helps engineers quickly select or specify an appropriate amplifier for a given gain requirement.
1 Impression