1 Introduction

Active analog-to-digital (ADC) front ends using a fully differential amplifier (FDA) can offer a host of advantages, such as better impedance matching, pass-band flatness and signal gain. However, if you require only a portion of the ADC’s band for your next design, it might be necessary to use an anti-aliasing filter (AAF) between the output of the FDA and the input of the ADC. An AAF will yield better signal-to-noise (SNR) performance and lower spurious or spurious-free dynamic range (SFDR) within your frequency band requirements.

With any kind of AAF filter constructions, you will have several trade-offs to consider during the implementation process: filter order and topology, or whether you will need back termination or series resistances to enhance the interface between the FDA and the ADC. In this paper, I’ll discuss these AAF nuances and how to circumvent any huddles you might encounter in your next design.