Selecting High-Linearity Mixers for Wireless Base Stations - Application Note - Maxim

Today's communication systems, such as wireless base stations, make strong demands on receiver sensitivity and large-signal performance. This article focuses on mixers, and describes key mixer performance issues and the basic parameters specified in data sheets. The article explains how to select the best mixer to optimize the receive channel. This article was also featured in Maxim's Engineering Journal, vol. 68 (PDF, 2.72MB). A similar article appeared in German in Elektronik Informationen in July 2008, and in English in High Frequency Electronics magazine in October 2009. Introduction The communication standards for wireless base stations—e.g., GSM, UMTS, and (now) LTE—define minimum specifications for various parameters including receiver sensitivity and performance in the presence of large signals. These key requirements make heavy demands on every functional block of the radio in a wireless base station. In the receive signal path, mixer performance has a major impact on the receiver's sensitivity and large-signal performance. This article describes key mixer performance issues and parameters to help you select the best mixer for your receive channel. A Wireless Base-Station Receiver To start, we first analyze the block diagram of a typical receiver used in wireless base stations (Figure 1). These receivers are called superheterodyne receivers because the received signal undergoes two consecutive downconversions to lower frequencies. As shown, the signal is received by the antenna and then filtered by RF filter 1, which is normally used to filter out trash signals. This filter output is then amplified by an LNA (low-noise amplifier), which normally has a very low noise figure.