Low Voltage SPM Detector
CMX631A
5.1.2 Aliasing
Due to the sampling nature of switched-capacitor filters used in the CMX631A, high frequency noise or
unwanted signals can alias into the passband, disrupting detection. External components must be chosen
carefully to avoid alias effects.
Possible Alias Frequencies:
12kHz Mode = 52kHz
16kHz Mode = 69kHz
If other filtering in the system has not attenuated these alias frequencies, capacitors should be employed
across resistors R1 and R4 to provide anti-alias filtering.
The low-pass cutoff frequency should be chosen to be approximately 20kHz to 25kHz for a 12kHz system, or
25kHz to 30kHz for a 16kHz system.
i.e.
1
C =
2 x p x f x (R1 or R4)
0
When anti-alias capacitors are used, an allowance must be made for reduced gain at the SPM frequency
(12kHz or 16kHz).
The ‘Clock-Out’ Pin
The Clock-Out pin is intended to drive the CMX631A Clock-In pin only. It is not recommended that it be used to
clock other devices within the host equipment.
ã 1998 Consumer Microcircuits Limited
10
D/631A/1
CMLMICRO [ CML MICROCIRCUITS ]
