1.5.3 Block Diagram Description
Amplifier
The input signal 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
315Hz and 650Hz. The signal to noise ratio must be 16dB or greater. The signal must be
consistent over a period of about 80ms. These decode criteria are continuously monitored and
the assessment is updated every 6ms; reference Figure 4.
Control Logic
This block categorises the nature of the signal into two decoded output states and controls the
output pin. See the Decode Output Truth Table in Section 1.5.4.
Level Detector
The level detector operates by measuring the level of the amplified input signal and comparing it
with a preset threshold. The level detector output goes to the Control and Output Logic block.
The data output is gated with the level detector’s output. The data output is valid only if the level
detector output is true.
Xtal/Clock Oscillator
If the on-chip Xtal oscillator is to be used, then external component X1 is 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
“DETECT”
CONDITIONS
0
1
No Signal
Call Progress Band:
Will detect 350+440, 400+450, 440+480
400, 425,440, 450, 480+620, 600 and 620Hz tones
Note that DETECT responds to the whole range of call progress tones from 315Hz to 650Hz.
Table 1 Decode Output Truth Table
ã 2001 Consumer Microcircuits Limited
7
D/673/5
CMLMICRO [ CML MICROCIRCUITS ]
