MX641DW Просмотр технического описания (PDF) - MX-COM Inc
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MX641DW Datasheet PDF : 16 Pages
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Dual SPM Detector
12
5. Applications
5.1.1 Input Configurations
Differential Input
Tip (a)
Ring (b)
INPUT AMP
-
+
MX641
VBIAS
MX641 PRELIMINARY INFORMATION
Common Mode Input
INPUT AMP
-
+
MX641
VBIAS
Figure 8: Input Configurations
5.1.2 Protection Against High Voltages
Telephone systems may have high d.c. and a.c. voltages present on the line. If the MX641 is part of a host equipment
that has its own signal input protection circuitry, there will be no need for further protection as long as the voltage on any
pin is limited to within VDD +0.3V and VSS -0.3V.
If the host system does not have input protection, or there are signals present outside the device's specified limits, the
MX641 will require protection diodes at its signal inputs (+ and -). The breakdown voltage of capacitors and the peak
inverse voltage of the diodes must be sufficient to withstand the sum of the d.c. voltages plus all expected signal peaks.
5.1.3 Aliasing
Due to the sampling nature of switched-capacitor filters used in the MX641, 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
R3, R4, R7 and R8 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. C
1
2 u S u f2 u R3
When anti-alias capacitors are used, an allowance must be made for reduced gain at the SPM frequency (12kHz or
16kHz).
© 1998 MXxCOM Inc.
www.mxcom.com Tele: 800 638-5577 910 744-5050 Fax: 910 744-5054
Doc. # 20480115.003
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
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