v
rms
=
v
pp
2

2
(1.3)
Similarly, noise in analog signals is often defined in terms of volts or
amperes, while in microwave it will be in terms of dBm. Noise is usually
represented as noise density per hertz of bandwidth. In analog circuits, noise
is specified as squared volts per hertz, or volts per square root of hertz. In
microwave circuits, the usual measure of noise is dBm/Hz or noise figure, which
is defined as the reduction in signal-to-noise ratio caused by the addition of
the noise.
In both analog and microwave circuits, an effect of nonlinearity is the
appearance of harmonic distortion or intermodulation distortion, often at new
frequencies. In low-frequency analog circuits, this is often described by the ratio
of the distortion components compared to the fundamental components. In
microwave circuits, the tendency is to describe distortion by gain compression
(power level where the gain is reduced due to nonlinearity) or third-order
intercept point (IP3).
Noise and linearity are discussed in detail in Chapter 2. A summary of
low-frequency analog and microwave design is shown in Table 1.2.
1.3 Radio Frequency Integrated Circuits Used in a
Communications Transceiver
A typical block diagram of most of the major circuit blocks that make up a
typical superheterodyne communications transceiver is shown in Figure 1.1.
Many aspects of this transceiver are common to all transceivers.
Table 1.2
Comparison of Analog and Microwave Design
Parameter
Analog Design
Microwave Design
(most often used on chip)
(most often used at chip
boundaries and pins)
Impedance
Z
in

Z
in

50
Z
out

0
Z
out

50
Signals
Voltage, current, often peak
Power, often dBm
or peak-to-peak
Noise
nV/

Hz
Noise factor F, noise figure NF
Nonlinearity
Harmonic distortion,
Third-order intercept point IP3
intermodulation, clipping