1 Introduction

In an effort to build smaller digital receivers, the aerospace and defense industry is embracing modern direct radio-frequency (RF) sampling analog-to-digital converters (ADCs). These ADCs eliminate RF mixing stages and are closer to the antenna, simplifying digital receiver designs while also saving cost and printed circuit board (PCB) area.

One critical (and often misunderstood) parameter is the ADC noise figure, which sets the amount of RF gain to detect very small signals. This article explains how to calculate the noise figure of an RF-sampling ADC, and illustrate how the ADC noise figure affects RF signal-chain designs.