DIODE LIMITERS
• also called clipper
WAVE SHAPING CIRCUITS
• used to clip off portions of signal
voltages
lt
above
b
or below
b l
certain
t i
levels.
POSITIVE LIMITER
NEGATIVE LIMITER
• As the input voltage goes positive, the
diode becomes forward-biased and
conducts current. Point A is limited to +0.7 V
when the input voltage exceeds this
• As the input voltage goes negative,
the diode becomes forward-biased
and conducts current. Point A is limited
to -0.7 V when the input voltage
exceeds
d thi
this
DIODE LIMITERS
PROBLEM
• What would you expect to see displayed on
an oscilloscope connected across RL in the
limiter?
 RL 
VOUT  
 VIN
R
R

L 
 1
BIASED LIMITERS
• The level to which an ac voltage is
limited can be adjusted by adding a
bias voltage, Vbias , in series with the
diode
NEGATIVE BIASED LIMITERS
• The voltage at point A must equal -Vbias - 0.7 V
before the diode will become forward-biased and
conduct.
• Once the diode begins to conduct, the voltage at
point A is limited to -V
Vbias
- 0.7
0 7 V so that all input
bi
voltage above this level is clipped off.
DIODE CLAMPERS
• used to add or restore a dc level to an
electrical signal
• sometimes
ti
k
known as dc
d restorers.
t
POSITIVE BIASED LIMITERS
• The voltage at point A must equal Vbias + 0.7 V
before the diode will become forward-biased and
conduct.
• Once the diode begins to conduct, the voltage at
point A is limited to Vbias
+ 0.7
0 7 V so that all input
bi
voltage above this level is clipped off.
PROBLEM
• Determine the output wave form
POSITIVE CLAMPER
• a diode clamper that inserts a positive dc level in the output
waveform.
• The operation of this circuit can be seen by considering the
first negative half-cycle of the input voltage. When the input
voltage initially goes negative,
negative the diode is forward-biased,
forward biased
allowing the capacitor to charge to near the peak of the
input
NEGATIVE CLAMPER