Radio Frequency Integrated Circuit Design

Figure 1.1 Typical transceiver block diagram.
This transceiver has a transmit side (Tx) and a receive side (Rx), which
are connected to the antenna through a duplexer that can be realized as a switch
or a filter, depending on the communications standard being followed. The
input preselection filter takes the broad spectrum of signals coming from the
antenna and removes the signals not in the band of interest. This may be
required to prevent overloading of the low-noise amplifier (LNA) by out-of-
band signals. The LNA amplifies the input signal without adding much noise.
The input signal can be very weak, so the first thing to do is strengthen the
signal without corrupting it. As a result, noise added in later stages will be of
less importance. The image filter that follows the LNA removes out-of-band
signals and noise (which will be discussed in detail in Chapter 2) before the
signal enters the mixer. The mixer translates the input RF signal down to the
intermediate frequency, since filtering, as well as circuit design, becomes much
easier at lower frequencies for a multitude of reasons. The other input to the
mixer is the local oscillator (LO) signal provided by a voltage-controlled oscillator
inside a frequency synthesizer. The desired output of the mixer will be the
difference between the LO frequency and the RF frequency.
At the input of the radio there may be many different channels or frequency