A Resonant Approach to Interfacing Amplifiers to Switched-Capacitor ADCs Application Note (AN-827)

High sampling rate analog-to-digital converters (ADCs) are commonly used to sample complex modulated signals at intermediate frequencies in modern wireless receiver designs. Often CMOS switched-capacitor based ADCs are selected for such designs due to their attractive low cost and power dissipation. These ADCs utilize an unbuffered front end directly coupled to the sampling network, which presents time varying input track-and-hold impedances to the amplifier driving the ADC. To effectively drive the ADC with minimal noise and distortion degradation of the wanted signal, it is necessary to design a passive network interface, which helps to reject wideband noise and transforms the track-and-hold impedance to present a more benign load impedance to the driving amplifier. A resonant approach for transforming the track-and-hold impedance to a more predictable load allowing precise design of antialiasing filters is presented at several common IF frequencies. SWITCHED-CAPACITOR ADCS