Call Progress Tone Detector
FX643
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
internally set at �½V
DD.
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.
©
1996 Consumer Microcircuits Limited
7
D/643/4
CMLMICRO [ CML MICROCIRCUITS ]
