MX631DW CMLMICRO [CML Microcircuits], MX631DW Datasheet - Page 5

• Manufacturer Part Number: MX631DW
• Description: LOW VOLTAGE SPM DETECTOR
• Manufacturer: CMLMICRO [CML Microcircuits]

© 1997 MX•COM, INC.
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
Low Voltage SPM Detector
Implementation Notes
Aliasing
MX631, be careful to avoid the effects of alias distortion
with the external components you choose.
If these alias frequencies are liable to cause problems
and/or interference, it is recommended that anti-alias
capacitors are used across input resistors R
provide a highpass cutoff frequency, in conjunction with
R
or 25kHz to 30kHz (16kHz system).
When anti-alias capacitors are used, make allowance for
reduced gain at the SPM frequency (12kHz or 16kHz).
Application Information ......
Input Gain Calculation
provided on-chip to set the sensitivity of the MX631 to
conform to the user's national level specification with
regard to ‘Must’ and ‘Must-Not’ decode signal levels.
assist in the determination of the required gain/
attenuation.
Step 1
Step 2
Step 3
1
(R
Due to the switched-capacitor filters employed in the
Possible Alias Frequencies:
Values of anti-alias capacitors should be chosen to
The input amplifier, with its external circuitry, is
With reference to Figure 4, the following steps will
Levels (dB)).
required ‘Must’ decode level. The lower line
represents your required ‘Must-Not’ decode level.
and the upper sloping line; drop a vertical line from
this point to the X-axis (Amplifier Gain (dB)).
indicates the MINIMUM Input Amp gain required for
reliable decoding of valid signals.
and the lower sloping line; drop a vertical line from
this point to the X-axis.
indicates the MAXIMUM allowable Input Amp gain.
level will not be detected as long as the amplifier gain
is no higher than this level.
4
) of approximately 20kHz to 25kHz (12kHz system)
12kHz Mode=
16kHz Mode=
Draw two horizontal lines from the Y-axis (Signal
Mark the intersection of the upper horizontal line
The point where the vertical line meets the X-axis
Mark the intersection of the lower horizontal line
The point where the vertical line meets the X-axis
Input signals at or below the ‘Must-Not’ decode
i.e. C =
2
The upper line represents your
x
52kHz
69kHz
1
x
www.mxcom.com Tele: 800 638 5577 910 744 5050 Fax: [phone]
f
0
x
R
1
1
and R
4
.
5
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Input Gain Components
components shown in Figures 2 and 3.
components (R
gain within the limits obtained in Steps 2 and 3.
figure outside these limits.
center of the calculated range. The graph in Figure 4 is
for calculations for the input gain components for an
MX631 using a V
Signal Input Protection
voltages present on the line. If the MX631 is part of 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 V
0.3V and V
there are signals present outside the device's specified
limits, the MX631 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.
The following paragraphs refer to the gain
The user should calculate and select external
Component tolerances should not move the gain-
It is recommended that the designed gain is near the
Telephone systems may have high d.c. and a.c.
If the host system does not have input protection, or
Use this area to keep a permanent record
of your calculated gains and components
SS
-0.3V.
1
, R
DD
2
/C
of 3.3 (±0.1) volts.
3
, R
3
/C
4
, R
4
) to provide an amplifier
Doc.# 20480087.003
MX631
DD
+