Jim Karki
Texas Instruments

This paper analyzes two approaches to using an FDA to attenuate and level-shift high-amplitude, SE bipolar signals to the input range of lower-voltage input ADCs. The first approach uses an input attenuator with values chosen to provide the required attenuation and to keep the noise gain of the FDA equal to 2 for stability. The second approach uses the gain setting resistors of the FDA in much the same way as using an inverting op amp, then a resistor is bootstrapped across the inputs to provide a noise gain of 2.