CMX641A データシートの表示（PDF） - MX-COM Inc

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CMX641A

Dual SPM/Security Detector/Generator

MX-COM Inc  

Dual SPM/Security Detector/Generator

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CMX641A Advance Information

4. General Description

4.1 Description of Blocks

4.1.1 Crystal Oscillator and Clock Dividers

These circuits derive the internal logic clocks, decode frequencies and transmit frequencies by frequency

division of a reference frequency that may be generated by the on-chip crystal oscillator or applied from an

external source.

If the on-chip oscillator is used, a 3.579545MHz crystal should be connected across the XTAL and XTALN

pins and CLOCK IN pin should be connected to CLOCK OUT. All other oscillator components are on-chip. If

an external clock source is used then it should be applied to the CLOCK IN pin and the XTAL pin connected to

VDD.

4.1.2 Input Operational Amplifiers

The input signals are input to the CMX641A via these amplifiers. In Controlled Sensitivity mode of the Fixed

Bandwidth Operating state, or when in Enhanced Features Operating state, the external components shown in

Figure 2 should be used. When used in the Fixed Sensitivity mode of the Fixed Bandwidth Operating state,

external gain setting components should be calculated using Figure 6.

In Enhanced Features Operating state, with the channels set to 12kHz/16kHz detect, the channel 2 amplifier

can optionally be isolated and may be used as an independent amplifier. In this case, both channels are

internally connected to amplifier 1. The amplifiers can be connected as differential mode or single ended,

depending upon the application (see Figure 3).

4.1.3 SPM Tone Bandpass Filter

These are tone bandpass/audio reject filters automatically centered on the system frequency (12kHz or

16kHz) being detected. When in Controlled Sensitivity mode of the Fixed Bandwidth Operating state or when

in Enhanced Features Operating state, the level sensitivity of the device is set by adjusting the passband gain

of these filters. When in Fixed Sensitivity mode of the Fixed Bandwidth Operating state, their gain is constant

so that the internal device sensitivity is also constant.

4.1.4 Level Detection and Pulse Generator Circuits

The outputs from the bandpass filters are input to these circuits, which perform the signal level discrimination

function for the CMX641A. Signals that fulfill the system level requirements cause a stream of digital pulses,

one per 32 cycles of input signal, to be generated. These pulses are sent to the period measurement circuitry.

4.1.5 Period Measurement Logic

This digital circuit block inputs the stream of pulses from the level detection circuits and measures their

repetition rate against a predetermined maximum and minimum. Because each pulse from the level detect

circuit occur once per 32 cycles of input signal, this has the effect of averaging the input signal period over this

number of cycles. A valid SPM tone is recognized when 3 successive correctly spaced pulses are received. If

the Tone Follower output format is selected, this causes a signal to appear immediately at the relevant

channel output signifying receipt of a valid SPM signal. Depending upon the frequency, within the legal

bandwidth, received, the CMX641A should respond within 10-15ms (see section 6 and Figure 5).

4.1.6 Tone Length Logic

This digital circuit block is used when Packet output format is selected. Its output responds when 40ms of

valid tone is received within any 48ms window, signifying receipt of a valid packet of SPM tone (see section 6).

Once the CMX641A has responded, within any 48ms window, 40ms of no-tone, or of tone outside the chosen

bandwidth or below the level threshold will cause the output to derespond. (See Figure 5).

4.1.7 Tx Tone Generator and Shaping Filter

These are active in Enhanced Features Operating state only. They generate a low distortion sinewave for

transmission by the CMX641A as an SPM security tone. The output at the TONE OP pin is modulated on-off

by the TONE ASK pin. A high (logic ‘1’) selects no tone and low (logic ‘0’) selects tone. The transmission

frequency is selected by the TX TONE SELECT pin. A high (logic ‘1’) selects 12kHz and a low (logic ‘0’)

selects 16kHz. (See Table 8).

ã2001 MX-COM, Inc.

www.mxcom.com Tel: 800 638 5577 336 744 5050 Fax: 336 744 5054

Doc. # 20480227.002

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

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