Dual SPM/Security Detector/Generator
CMX641A
1.3
External Components
Figure 2 Recommended External Components
Fixed Bandwidth Operating State,
Controlled Sensitivity Mode
and
Enhanced Features Operating State
R1
R2
R3
R4
R5
R6
R7
R8
68kΩ
68kΩ
750kΩ
750kΩ
68kΩ
68kΩ
750kΩ
750kΩ
±1%
±1%
±1%
±1%
±1%
±1%
±1%
±1%
C1
C2
C3
C4
C5
C6
X1
1.0µF
1.0µF
270pF
270pF
270pF
270pF
3.579545MHz
±20%
±20%
±5%
±5%
±5%
±5%
Fixed Bandwidth Operating State,
Fixed Sensitivity Mode
In this mode input amplifier components are chosen to set the required sensitivity of the CMX641A. (See
section 1.6.5).
Note that when calculating/selecting gain components, R3, R4, R7 and R8 should always be greater than
or equal to 100kΩ.
Particular attention should be paid to decoupling V
DD
and keeping the power, ground and signal lines free
from unnecessary noise.
Telephone systems may have unusually high dc and ac voltages present on the line, as either differential
or common mode signals. If the CMX641A is part of a host system which does not have its own input
protection, then protection diodes must be added to both signal inputs (+ and -) so that the voltage on any
pin is limited to within V
SS
– 0.3V and Vdd + 0.3V. The breakdown voltage of capacitors and the peak
inverse voltage of diodes must be sufficient to withstand the sum of the dc and peak-peak ac voltages
applied.
©
2002 Consumer Microcircuits Limited
8
D/641A/5
CMLMICRO [ CML MICROCIRCUITS ]
