Baseband Processor For Mixed Mode Land Mobile Radio
CMX880
AC Parameters (cont.)
Notes
Min.
Typ.
Max.
Units
Receiver Signal Type Identification
Probability of correctly identifying signal type
(SNR = 12dB)
>>99.9
%
CTCSS Detector
Sensitivity
(Pure Tone)
(Composite Signal)
(Composite Signal)
51
52
52
-26
140
145
dB
ms
ms
Hz
Response Time
De-response Time
Frequency Range
250
260
60
SELCALL Detector
Sensitivity
(Pure Tone)
(Good Signal)
(Good Signal)
(Selcall)
53
51
-26
14
22
dB
ms
ms
Hz
Response Time
De-response Time
Frequency Range
300
58
3000
1000
DCS Decoder
Sensitivity
mVp-p
edges
Bit-Rate Sync Time
2
FFSK/MSK Decoder
Signal Input Dynamic Range
Bit Error Rate
(SNR = 50dB)
54
54
100
230
mVrms
(SNR = 12dB at 1200 baud)
(SNR = 12dB at 2400 baud)
(SNR = 20dB at 1200/2400 baud)
2.5
1.5
<1
10-4
10-3
10-8
Receiver Synchronisation
(SNR = 12dB)
Probability of bit 16 being correct
>99.9
%
C4FM Decoder
Input Signal Level
55
55
1000
+50
mVrms
mV
S/s
DC Offset wrt VDD /2
Symbol Rate
Maximum Symbol Rate Drift
Bit Error Rate
-50
4800
40
4
56
57
57
ppm
(SNR = 12dB)
(SNR = 16dB)
10-4
2
10-6
Notes:
51.
52.
Sub-Audio Detection Level threshold set to 16mV.
Composite signal = 308mV rms at 1kHz + 75mV rms Noise + 31mV rms Sub-Audio
signal. Noise bandwidth = 5kHz Band Limited Gaussian.
53.
54.
Selcall Tone Detection Level threshold set to 16mV.
For a “101010101 ... 01” pattern. See Figure 25 and Figure 26 for variation of BER
with SNR and with input signal level.
55.
56.
57.
For optimum performance, measured at FM_DISC input pin, for a “+3 +3 - 3 - 3 ...”
symbol sequence, with VDD = 5V and the Unit Level set to 2048. The optimum
levels and DC offset values are proportional to VDD
.
The CMX880 will track and decode received symbol sequences with up to this
symbol rate error wrt to the local clock. BER increases by ~10-4 per 10ppm drift, at
SNR = 12dB.
See graph shown in Figure 27. Noise Bandwidth = bit rate bandwidth (bit rate
bandwidth = 2 ´ C4FM symbol rate = 0 to 9600Hz).
AC Parameters (cont.)
Notes
Min.
Typ.
Max.
Units
ã 2001 Consumer Microcircuits Limited
73
D/880/1
CMLMICRO [ CML MICROCIRCUITS ]
