© 1999 Consumer Microcircuits Limited

8

D/663/3

Minimum Input Signal: The minimum signal level for the specified tone decoding performance. The lower

level at which absence of an input signal will be registered is not specified. However, a separate level detector

makes amplitude information available.

No Signal: A signal falling outside the nominal range 180Hz to 2280Hz 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)

Amplifier

The input signal is amplified by a self-biased inverting amplifier. The dc bias of this input is internally set at

Call Progress Detector: 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 700Hz, the

signal to noise ratio must be 16dB or greater and the signal must be consistent over a period of at least

145ms. These decode criteria are continuously monitored and the assessment is updated every 7ms.

620Hz Detector

The detector is designed to aid detection of "US Busy" tone. The bandwidth of the 620Hz Detector is 60Hz

and the signal must be consistent over a period of at least 145ms for detection to occur. This assessment is

updated every 55ms.

Control and Output Logic

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

outputs. See the Truth Table in section 1.5.4.

Level Detector and OPAMP

The OPAMP is configured as an amplifier with external components R1, R2, C4 and C5. The level detector

operates by measuring the level of the amplified input signal and comparing it with a preset threshold which is

defined inside the FX663 as shown in the detect equation.

The 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. The level detector output can

An interrupt is produced if the output data changes state.

The detect equation is:

For detect level

Gain x input signal level > 250 mVp-p

where gain = -R2/R1.

This amplifier may be used to buffer, unbalance or amplify line signals if required.

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.