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Pulse-Position Modulation

See Figure 20

Capacitor Voltage

Output Voltage

Modulation Input Voltage

Time − 0.1 ms/div

Modulation

Input

(see Note A)

CONT

TRIG

RESET

OUT

DISCH

C

GND

THRES

NOTE A: The modulating signal can be direct or capacitively coupled

to CONT. For direct coupling, the effects of modulation

source voltage and impedance on the bias of the timer

should be considered.

Pin numbers shown are for the D, JG, P, PS, and PW packages.

4

8

3

7

6

2

5

Output

NA555, NE555, SA555, SE555

PRECISION TIMERS

SLFS022G – SEPTEMBER 1973 – REVISED MARCH 2008

As shown in Figure 20, any of these timers can be used as a pulse-position modulator. This application

modulates the threshold voltage and, thereby, the time delay, of a free-running oscillator. Figure 21 shows a

triangular-wave modulation signal for such a circuit; however, any wave shape could be used.

Figure 20. Circuit for Pulse-Position Modulation

Figure 21. Pulse-Position-Modulation Waveforms

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Product Folder Link(s): NA555 NE555 SA555 SE555