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NE567

Tone decoder/phase-locked loop

Philips Electronics 

Philips Semiconductors Linear Products

Tone decoder/phase-locked loop

Product specification

NE/SE567

CHATTER PREVENTION (Figure 4)

Chatter occurs in the output stage when C3 is relatively small, so

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

making C3 large, the feedback circuit will enable faster operation of

the 567 by allowing C3 to be kept small. Note that if the feedback

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)

ADJUSTMENT (Figure 5)

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

or the other of the center frequency. Since RB also alters the duty

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

REDUCTION (Figure 6)

Although a large value of C2 will reduce the bandwidth, it also

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

impedance level at terminal 2 will require that a larger value of C2 be

used for a given filter cutoff

frequency. If more than three 567s are to be used, the network of RB

and RC can be eliminated and the RA resistors connected together.

A capacitor between this junction and ground may be required to

shunt high frequency components.

OUTPUT LATCHING (Figure 7)

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

For precision very low-frequency applications, where the value of C1

becomes large, an overall cost savings may be achieved by

inserting a voltage-follower between the R1 C1 junction and Pin 6,

so as to allow a higher value of R1 and a lower value of C1 for a

given frequency.

PROGRAMMING

To change the center frequency, the value of R1 can be changed

with a mechanical or solid state switch, or additional C1 capacitors

may be added by grounding them through saturating NPN

transistors.

April 15, 1992

412

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