So far device models and the parameter sets have been presented. It is now important to develop the major building blocks of modern RF circuits and this chapter will cover amplifier design. The amplifier is usually required to provide low noise gain with low distortion at both small and large signal levels. It should also be stable, . not generate unwanted spurious signals, and the performance should remain constant with time. | Fundamentals of RF Circuit Design with Low Noise Oscillators. Jeremy Everard Copyright 2001 John Wiley Sons Ltd ISBNs 0-471-49793-2 Hardback 0-470-84175-3 Electronic 3 Small Signal Amplifier Design and Measurement Introduction So far device models and the parameter sets have been presented. It is now important to develop the major building blocks of modern RF circuits and this chapter will cover amplifier design. The amplifier is usually required to provide low noise gain with low distortion at both small and large signal levels. It should also be stable . not generate unwanted spurious signals and the performance should remain constant with time. A further requirement is that the amplifier should provide good reverse isolation to prevent for example LO breakthrough from re-radiating via the aerial. The input and output match are also important when for example filters are used as these require accurate terminations to offer the correct performance. If the amplifier is being connected directly to the aerial it may be minimum noise that is required and therefore the match may not be so critical. It is usually the case that minimum noise and optimum match do not occur at the same point and a circuit technique for achieving low noise and optimum match simultaneously will be described. For an amplifier we therefore require 1. Maximum specified gain through correct matching and feedback. 2. Low noise. 3. Low distortion. 4. Stable operation. 98 Fundamentals of RF Circuit Design 5. Filtering of unwanted signals. 6. Time independent operation through accurate and stable biasing which takes into account device to device variation and drift effects caused by variations in temperature and ageing. It has been mentioned that parameter manipulation is a great aid to circuit design and in this chapter we will concentrate on the use of y and S parameters for amplifier design. Both will therefore be described. Amplifier Design Using Admittance Parameters Ay parameter .
