Dual SPM Detector
SIGNAL INPUT
TONE
Page 8 of 16
NOTONE
MX641 Preliminary Information
CH1 and CH 2 OUTPUTS
TONE FOLLOWER OUTPUT
PACKET MODE OUTPUT
RESPONSE
DELAY
SIGNAL INPUT ......
TONE FOLLOWER OUTPUT ......
DERESPONSE
DELAY
PACKET MODE OUTPUT ......
Figure 4: Tone Follower and Packet Mode Outputs
4.3
Sensitivity Setting
To enable the MX641 to operate correctly to most national 12kHz and 16kHz SPM specifications, the input
sensitivity can be accurately adjusted and set.
There are two different pin-selectable modes of sensitivity setting available to the MX641: Controlled
Sensitivity Mode and Fixed Sensitivity Mode
The Controlled Sensitivity mode allows the sensitivity setting from a µController via a 6-bit serial data input.
This same serial input also sets operation (bit 0) to either 12kHz or 16kHz systems. Both channels are set
identically.
The Fixed Sensitivity mode allows the sensitivity of each channel to be set to a fixed “gain” by external
components at the input amplifiers. Operation to either 12kHz or 16kHz is by the System Select input.
4.3.1
Controlled Sensitivity Setting
With the external gain (sensitivity) components used as shown in Figure 2, the gain of the input stages is
19.8dB (12kHz) or 20.5dB (16kHz). For controlled sensitivity setting the gain of each bandpass filter, and
therefore the device sensitivity, is adjusted by the applied serial bits D1 to D5.
In the Controlled Sensitivity mode the system frequency is selected by bit D0 (‘1’ = 12kHz; ‘0’ = 16kHz). Data
is loaded Bit 5 (D5) first. Table 4 details the serial data inputs for the required sensitivity. Minimum, Nominal
and Maximum Sensitivity figures are provided to make complete allowance for internal circuit offsets and
component tolerances.
0dB(ref.) = 775mV
RMS
at V
DD
= 5.0 volts; varies directly with V
DD
.
Note: Device sensitivity is directly proportional to V
DD
ã
2001 MX-COM, Inc.
www.mxcom.com tel: 800 638 5577 336 744 5050 fax: 336 744 5054
Doc. # 20480115.004
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
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