Page 310 - Mechatronics with Experiments

JWST499-Cetinkunt
JWST499-c05
296 MECHATRONICS Printer: Yet to Come October 28, 2014 11:15 254mm×178mm
V out
5 V

V in V out V
2 3 4 V in

(a) (b)
V in

V ht

V LT

Time
IC
input

Time
Schmitt IC
trigger input
output

Time
(c)
FIGURE 5.32: Schmitt trigger circuit in digital circuits: (a) symbol, (b) input–output
relationship, (c) a noisy input signal, ON/OFF signal at the input port of an IC without Schmitt
trigger, and ON/OFF signal after it passes through the Schmitt trigger, which is also referred to
as switch-debouncing.

For case 2, the width of the hysteresis voltage, V is
T
R 2 100 000
V = ⋅ V sat = ⋅ 13 (5.228)
T
R + R 2 100 000 + 100 000
1
= 6.5 V (5.229)
In this case, the output voltage switches between the V sat =+13 V and −V sat =−13 V when
the input signal goes through the hysteresis band of +6.5 V and −6.5 V. The hysteresis
magnitude is large and visually observed on the figure. The input signal and output signal
for both of the cases above are shown in Figure 5.33.