4-8
During T1 to T2 the anode is negative with respect to the cathode and the diode does not conduct.
This portion of the output is limited because no current flows through the resistor.
As you can see, the only difference between series-positive and series-negative limiters is that the
diode is reversed in the negative limiters.
SERIES-NEGATIVE LIMITER WITH BIAS.—View (A) of figure 4-7 shows a series-negative
limiter with negative bias. The diode is forward biased and conducts with no input signal. In view (B) it
will continue to conduct as the input signal swings first positive and then negative (but only to
-
5 volts)
from T0 through T1. At T1 the input becomes negative with respect to the
-
5 volt battery bias. The diode
becomes reverse biased and is cutoff until T2 when the anode again becomes positive with respect to the
battery voltage (
-
5 volts) on the cathode. No voltage is developed in the output by R1 (no current flow)
and the output is held at
-
5 volts from T1 to T2. With negative bias applied to a series-negative limiter,
only a portion of the negative signal is limited.
Figure 4-7A.—Series-negative limiter with negative bias.
Figure 4-7B.—Series-negative limiter with negative bias.
Now let's look at a series-negative limiter with positive bias, as shown in figure 4-8, view (A). Here
we will remove all of the negative alternation and part of the positive alternation of the input signal. We
have given a full explanation of the series-positive limiter, series-positive limiter with bias, series-
negative limiter, and series-negative limiter with negative bias; therefore, you should have little difficulty
understanding what is happening in the circuit in the figure.
