Call Progress Tone Detector
FX633
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. To
be classified as a call progress signal the input signal frequencies should lie between 340Hz and
650Hz. 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.
Xtal/Clock Oscillator
If the on-chip Xtal oscillator is to be used, then external components X1, R1, C1 and C2 are required.
If an external clock source is to be used, then it should be connected to the XTAL/CLOCK input pin
and the XTALN pin should be left unconnected.
1.5.4 Decode Output Truth Table
DETECT2
DETECT1
CONDITIONS
0
0
1
1
0
1
1
0
No Signal
Call Progress Low Band:
Will detect 350+440, 400+450, 440+480,
400, 425, 440, and 450Hz tones
Call Progress High Band:
Will detect 480+620, 600 and 620Hz tones
Non Call Progress signal, e.g. Voice Activity
Note that DETECT1 responds to the whole range of call progress tones from 340Hz to 650Hz.
1.6
Application Notes
1.6.1 General
On power-up, a logic "0" at the ENABLE input may be used to disable and initialise the
device.
ã 1996 Consumer Microcircuits Limited
7
D/633/3
CMLMICRO [ CML MICROCIRCUITS ]
