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11.3.3 
ramp response of series 
RC
 circuit 
Here too we employ the integration method to arrive at the zero-state response to unit ramp input 
from the zero-state response to unit step input since unit ramp waveform is the integral of unit step 
waveform.
Ramp response, 
C
v t
e
dt
t
e
t
e
t
t
t
t
t
( )
(
)
(
)
=
−
= +
= −
−
−
−
−
+
+
∫
1
1
0
0
t
t
t
t
t
V
V for t
≥
+
0
Ramp waveform finds application in many contexts in electronics, instrumentation and signal 
processing. It is used as the internal time-base waveform in oscilloscopes. It is used in timing and 
counting applications too. Some dedicated electronic circuitry generates this ramp waveform and 
the generated waveform is conducted to the application circuit by means of a two-wire connection. 
This two-wire connection can often be modelled approximately by a Series RC Circuit where the 
resistor is contributed by the output resistance of the generator circuit (i.e., the resistor that appears 
in the Thevenin’s equivalent of the generator circuit output) and the capacitor is contributed by the 
input capacitance of the application circuit. The ramp waveform gets modified in this process of 
transmission from the output of generator circuit to the input of the application circuit. We observe 

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Zero-StateResponseof
RC
CircuitsforVariousInputs

11.9
from the above expression for ramp response of Series RC Circuit that the ramp waveform suffers 
two modifications – in the initial portion, i.e., for t << 
t
, the output fails to follow the linear 
variation of input and is rather prominently an exponential waveform. For t >> 
t
the output follows 
the input; but with a constant difference of 
t
V. Hence, we may conclude that a Series RC Circuit 
will be able to transmit a ramp waveform more or less faithfully if the waveform duration is 
significantly larger than the time constant of the circuit. The waveforms in Fig. 11.3-6 show this
clearly.
Volts
t
t
– 
(1 – exp(–
t
/
))
Time
– 
(1 – exp(–
t
/
))
τ
τ
τ
τ
τ
V
C
(
t
)
Fig. 11.3-6 
Unitrampresponseofseries
RC
circuit