Philips Semiconductors Linear Products

Product specification

NE/SE567

Tone decoder/phase-locked loop

April 15, 1992

412

that the lock transient and the AC components at the quadrature

phase detector (lock detector) output cause the output stage to

move through its threshold more than once. Many loads, for

example lamps and relays, will not respond to the chatter. However,

logic may recognize the chatter as a series of outputs. By feeding

the output stage output back to its input (Pin 1) the chatter can be

eliminated. Three schemes for doing this are given in Figure 4. All

operate by feeding the first output step (either on or off) back to the

input, pushing the input past the threshold until the transient

conditions are over. It is only necessary to assure that the feedback

time constant is not so large as to prevent operation at the highest

anticipated speed. Although chatter can always be eliminated by

time constant is made quite large, a short burst at the input

frequency can be stretched into a long output pulse. This may be

useful to drive, for example, stepping relays.

DETECTION BAND CENTERING (OR SKEW)

When it is desired to alter the location of the detection band

(corresponding to the loop capture range) within the lock range, the

circuits shown above can be used. By moving the detection band to

one edge of the range, for example, input signal variations will

expand the detection band in only one direction. This may prove

useful when a strong but undesirable signal is expected on one side

cycle slightly, this method may be used to obtain a precise duty

cycle when the 567 is used as an oscillator.

ALTERNATE METHOD OF BANDWIDTH

reduces the loop damping so as to slow the circuit response time.

This may be undesirable. Bandwidth can be reduced by reducing

the loop gain. This scheme will improve damping and permit faster

operation under narrow-band conditions. Note that the reduced

used for a given filter cutoff

A capacitor between this junction and ground may be required to

shunt high frequency components.

To latch the output on after a signal is received, it is necessary to

provide a feedback resistor around the output stage (between Pins 8

and 1). Pin 1 is pulled up to unlatch the output stage.

REDUCTION OF C1 VALUE

becomes large, an overall cost savings may be achieved by

given frequency.

PROGRAMMING

may be added by grounding them through saturating NPN

transistors.