Pulse and Digital Circuits

3.2 LOW-PASS CIRCUITS

Low-pass circuits derive their name from the fact that the output of these circuits is larger for lower frequencies and vice-versa. Figures 3.1(a) and (b) represent a low-pass RC circuit and a low-pass RL circuit, respectively.

In the RC circuit, shown in Fig. 3.1(a), at low frequencies, the reactance of C is large and decreases with increasing frequency. Hence, the output is smaller for higher frequencies and vice-versa. Similarly, in the RL circuit shown in Fig. 3.1(b), the inductive reactance is small for low frequencies and hence, the output is large at low frequencies. As the frequency increases, the inductive reactance increases; hence, the output decreases. Therefore, these circuits are called low-pass circuits. Let ...