Radio Frequency Integrated Circuit Design

2.1 Introduction
In this chapter we will have a brief look at some general issues in RF circuit
design. Nonidealities we will consider include noise and nonlinearity. We will
also consider the effect of filtering. An ideal circuit, such as an amplifier, produces
a perfect copy of the input signal at the output. In a real circuit, the amplifier
will introduce both noise and distortion to that waveform. Noise, which is
present in all resistors and active devices, limits the minimum detectable signal
in a radio. At the other amplitude extreme, nonlinearities in the circuit blocks
will cause the output signal to become distorted, limiting the maximum signal
amplitude.
At the system level, specifications for linearity and noise as well as many
other parameters must be determined before the circuit can be designed. In
this chapter, before we look at circuit details, we will look at some of these
system issues in more detail. In order to design radio frequency integrated
circuits with realistic specifications, we need to understand the impact of noise
on minimum detectable signals and the effect of nonlinearity on distortion.
Knowledge of noise floors and distortion will be used to understand the require-
ments for circuit parameters.
2.2 Noise
Signal detection is more difficult in the presence of noise. In addition to the
desired signal, the receiver is also picking up noise from the rest of the universe.