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

SLFS022H – SEPTEMBER 1973 – REVISED JUNE 2010

www.ti.com

Pulse-Position Modulation

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

14

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