Slew rate determines how fast an op-amp switches
from an OFF (low) to an ON (high) state. If the device
has a high slew rate, then it can switch from high(low) to
low(high) in a shorter period of time [5]. General purpose opamps
that have slew rate between 0.5 to 1 VI fJS, hence cannot
respond to fast changing, highfrequency signals. This effect
can be demonstrated using Fig.2. The input to the window
cOluparator circuit is a triangular signal having a rise time
of 40fJs. As the op-amps used in the simulation had a slew
rate of only 1 VI fJs, it was not able to respond fast enough to
the fast changing signal. If the signalfrequency is increased
further, the circuit fails to respond at all. Hence slew rate
becomes an important parameter when designing a circuit with
high frequency signals. If measurement of time base is the
objective of window comparator, then the slew of the window
comparator should at least be 1 ° times the input signal slewing.
This means that we require very fast op-amps of the order of
5 to 10 V/fJs.