FSK Modem and DTMF Codec
CMX865
Notes:
I/P
O/P
BI
T/S
NC
=
=
=
=
=
Input
Output
Bidirectional
3-state Output
No Connection
4.
External Components
R1
X1
68kΩ
11.0592MHz
or 12.288MHz
C1, C2
C3, C4
C5
22pF
100nF
10uF
Resistors
±5%,
capacitors
±20%
unless otherwise stated.
Figure 2 Recommended External Components for a Typical Application
This device is capable of detecting and decoding small amplitude signals. To achieve this, V
DD
and V
BIAS
should be decoupled and the receive path protected from extraneous in-band signals. It is recommended
that the printed circuit board is laid out with a V
SS
ground plane in the CMX865 area to provide a low
impedance connection between the V
SS
pins and the V
DD
and V
BIAS
decoupling capacitors. The V
SS
connections to the Xtal oscillator capacitors C1 and C2 should also be low impedance and preferably be
part of the V
SS
ground plane to ensure reliable start up of the oscillator.
For best results, an Xtal oscillator design should drive the clock inverter input with signal levels of at least
40% of V
DD
peak-to-peak. Tuning-fork Xtals generally cannot meet this requirement. To obtain Xtal
oscillator design assistance, please consult your Xtal manufacturer.
©
2005 CML Microsystems Plc
5
D/865/3
CMLMICRO [ CML MICROCIRCUITS ]
