SL6679
SL6679
VCC
VREF15mV
CURRENT
SOURCE 1
−
30
−
100k
+
+
32
31
R13
C34
R17
C18
RDECAY
CTC
VREF
VREF
Fig.3 AGC schematic
RF
INPUT
VCC1
TO RF AMP
VOLTAGE
REFERENCE
AFC
DETECTION
CIRCUIT
SL6679
18
VCC2
0µA/5µA
19
5µA/0µA
24
CVREF
C15
CINT 1
R15
VCC1
R11 C21
25
C22
C30
CINT 2
320k
TO VCXO
VARACTOR
DIODE
Fig. 4 AFC schematic
Peak deviation
(kHz)
Baud rate
(bps)
Component (Fig. 4)
C22 C21 R11
3·5
512, 1200, 2400 750pF 2·0nF 15kΩ
4
512, 1200, 2400 560pF 1·5nF 15kΩ
4·5
512, 1200, 2400 510pF 1·3nF 15kΩ
5
512, 1200, 2400 470pF 1·2nF 15kΩ
5·5
512, 1200, 2400 430pF 1·1nF 15kΩ
Table 2 AFC defining components
10