4-39
The amount of integration is dependent upon the values of R and C. The amount of integration may
also be dependent upon the time constant of the circuit. The time constant of the circuit should be at least
10 TIMES GREATER than the time duration of the input pulse for integration to occur. The value of 10
is only an approximation. When the time constant of the circuit is 10 or more times the value of the
duration of the input pulse, the circuit is said to possess a long time constant. When the time constant is
long, the capacitor does not have the ability to charge instantly to the value of the applied voltage.
Therefore, the result is the long, sloping, integrated waveform.
Q18. What are the requirements for an integration circuit?
Q19. Can a pure sine wave be integrated? Why?
RL INTEGRATORS
The RL circuit may also be used as an integrating circuit. An integrated waveform may be obtained
from the series RL circuit by taking the output across the resistor. The characteristics of the inductor are
such that at the first instant of time in which voltage is applied, current flow through the inductor is
minimum and the voltage developed across it is maximum. Therefore, the value of the voltage drop across
the series resistor at that first instant must be 0 volts because there is no current flow through it. As time
passes, current begins to flow through the circuit and voltage develops across the resistor. Since the
circuit has a long time constant, the voltage across the resistor does NOT respond to the rapid changes in
voltage of the input square wave. Therefore, the conditions for integration in an RL circuit are a long time
constant with the output taken across the resistor. These conditions are shown in figure 4-33.
Figure 4-33.—RL integrator waveform.
Q20. What characteristic of an RL circuit allows it to act as an integrator?
INTEGRATOR WAVEFORM ANALYSIS
If either an RC or RL circuit has a time constant 10 times greater than the duration of the input pulse,
the circuits are capable of integration. Let's compute and graph the actual waveform that would result
