Agilent Technologies

Practical RF Ampli er Design Using the

Available Gain Procedure and the

Advanced Design System EM/Circuit

Co-Simulation Capability

White Paper by Ken Payne

Figure 1

Abstract

This article features a method of designing a low noise RF amplifier for an 802.11b receiver application and contains an Avago ATF54143 PHEMT transistor. ADS design tools are used such that the techniques presented remove much of the guesswork from the design pro-cess. Design speed and cost along with RF performance are of utmost importance for most RF designs, thus, one of the main objectives is to yield a design that works with the first PCB pass. If successful, multiple PCB layouts are avoided, which saves design cost and time. This design procedure is considered successful even if some of the lumped component values have to be adjusted slightly to get the desired RF performance – as long as the layout does not have to be modified to have a working circuit. It is also considered success-ful even if the model prediction doesn’t exactly agree with measured results, but the resulting circuit still meets the design criteria and specifications. The featured amplifier covers a frequency range of 2.4 GHz to 2.48 GHz. The design is illustrated from start to finish, with construction of a printed circuit board and measurement results.

Introduction

An ampli er circuit consists mainly of a gain device or devices, and input and output matching or coupling networks. The ampli er should make weak signals larger without adding too much noise or distortion. Ideally, the ampli er would add no noise and would not distort the signal in any way. Electronic devices are not ideal however, and thus degrade the signal to some degree. The ampli er design objective is to minimize the noise added and the distortion created while increasing the amplitude of the signal. Design trade-offs allow one to obtain the best possible performance from a particular active device.