Call Progress Tone Detector

FX643

© 1996 Consumer Microcircuits Limited

7

D/643/4

No Signal: A signal falling outside the nominal range 120Hz to 900Hz or Special Information Tone or

the absence of an input signal. Either will be detected as a No Signal condition.

Nominal: Subject to dynamic tolerances within the signal analysis process. Absolute values are not

material or adverse to performance.

1.5.3

Block Diagram Description

(reference Figure 1)

Slicer

The input signal to the slicer is amplified by a self-biased inverting amplifier. The dc bias of this input is

Signal Analyser

The frequency range, quality and consistency of the input signal is analysed by this functional block.

The signal to noise ratio must be 16dB or greater. The signal must be consistent over a period of

about 140 ms. These decode criteria are continuously monitored and the assessment is updated

every 7 ms, reference Figure 3.

The analyser samples the call progress signal at 9.3kHz; so care should be taken to avoid high

frequency signals (e.g. 18kHz) aliasing into the call progress band.

Control Logic

This block categorises the nature of the signal into various decoded output states and controls the two

output pins. See the Decode Output Truth Table in section 1.5.4.

Clock

An external clock source is to be connected to the XTAL/CLOCK input pin. Alternatively, the internal

oscillator may be used with an external crystal if the 16-pin SOIC (D4) version of the FX643 is used.