FRS/PMR446/GMRS Family Radio Processor
CMX838
4.1.8 Deviation Limiter
The purpose of the deviation limiter is to limit the signal level at baseband prior to reaching the RF modulator.
This is necessary to avoid co-channel interference as well as conform to the spectral constraints stipulated by
regulatory agencies (e.g. FCC). Figure 14 is a block diagram of the limiter circuitry. Applying a DC voltage
between VDD and VDD/2 to the reference input sets the maximum peak-to-peak signal level. This reference is
internally set so the maximum signal level is 2.196VP-P and is constant over supply voltage.
REFI N
TX AUDIO
LIMITED SPEECH TO
POST DEVIATION
LIMITER FILTER
-1
Figure 14: Deviation limiter block diagram.
2003 CML Microsystems Plc
16
D/838/8