Figure 17.21 shows the amplitude spectrum for output voltage
while that of the input voltage is in Fig. 17.4(a). Notice that the
two spectra are close. Why? We observe that the circuit in Fig. 17.20
is a highpass filter with the corner frequency
which is less than the fundamental frequency The dc
component is not passed and the first harmonic is slightly attenuated,
but higher harmonics are passed. In fact, from Eqs. (17.6.1) and
(17.6.2), is identical to for large n, which is characteristic of a
highpass filter.