Dual SPM Detector

Page 8 of 16

MX641 Preliminary Information

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ã2001 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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SIGNAL INPUT

TONE

NOTONE

RESPONSE

DELAY

DERESPONSE

DELAY

SIGNAL INPUT ......

TONE FOLLOWER OUTPUT

CH1 and CH 2 OUTPUTS

PACKET MODE OUTPUT ......

TONE FOLLOWER OUTPUT ......

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.