section - Bitsavers

PHASE LOCKED LOOP APPLICATIONSd.)e.)Use the desensitizing technique, also describedin the data sheet, to balance turn-on andturn-off delay.Apply the chatter prevention technique toclean up the output.If this procedure results in a worst-case response time thatis too slow, the following suggestions may be considered:a.)b.)c.)d.)e.)Relax the bandwidth requirement.Operate the entire system at higher frequencywhen this option is available.Use two tone decoders operating at slightlydifferent frequencies and OR the outputs. Thiswill reduce the statistical occurance of theworst-case lotk-up time so that excessive lockuptime occurs. For example, if the lock-uptime is marginal 10% of the time with one unit,it will drop to 1% with two units.Control the in~band input amplitude to stabilizethe bandwidth, set up two tone decoders formaximum bandwidth and overlap the detectionbands to make the desired frequency rangeequal to the overlap. Since both tone decodersare on only when a tone appears within theoverlap range, the outputs can be ANDed toprovide the desired selectivity.If the system design permits, send the tone tobe detected continuously at a low level (say25mV rms) to keep the loop in lock at alltimes. The output stage, slightly desensitized,can then be gated on as required by increasingsignal the amplitude during the on time.Naturally, the signal phase should be maintainedas the amplitude is changed. This schemeis extremely fast, allowing repetition rates asfast as 1/3 to 1/2 the center frequency when C3is small. This is equivalent to ASK (amplitudeshift keying).47