GMSK Packet Data Modem and RF Transceiver
CMX990
Figure 25 Block Diagram of CMX990 Showing use of External Receive Mixer
Signal to Noise
The performance of the receiver is based on the signal to noise performance of the demodulator. This
has been shown to achieve the Mobitex error rate limit of 1 in 100 BER at 9dB C/N.
Dynamic Range, RSSI and AGC
The dynamic range of the receiver must be partitioned between various requirements. Key to this is the
dynamic range of the ADC within IC that converts the I/Q signals into the digital domain. These
converters have a dynamic range of at least 85dB. This must be partitioned between various factor such
as filtering headroom, signal noise, quantisation noise margin etc. leaving an operating window. The
proposed partition is shown in Figure 26. Other partitions are possible depending on adjacent channel
requirements, external filtering, external gains etc.
ã 2004 CML Microsystems Plc
67
D/990/1
CMLMICRO [ CML MICROCIRCUITS ]
