Single Time Constant(STC) circuits

SINGLE TIME CONSTANT CIRCUITS:-

Study of these networks are important in designing of various amplifiers and filters which i'll discuss later.

An STC network is one that is composed of, or can be reduced to, one reactive component (inductance or capacitance) and one resistance. An STC network formed of an inductance L and a resistance R has a time constant T = L/R. The time constant T of an STC network composed of a capacitance C and a resistance R is given by T = CR.

Most of the STC networks can be classified in two categories:-
1.low pass network
2.high pass network

figures of both types of network are given below:-

(a)low pass network

 

(b)high pass network

 

the reason for such classification of STC networks is the reactance of a capacitor varies with frequency (Z = 1/jwC) it is easy to see that the transmission of
the circuit in Fig.(a) will decrease with frequency and approach zero as w approaches infinity.Thus the circuit of Fig.(a) acts as a low-pass filter;it passes low-frequency sine-wave inputs with little or no attenuation (at w = 0, the transmission is unity) and attenuates high-frequency input sinusoids. The circuit of Fig.(b) does the opposite; its transmission is unity at w = infinity  and decreases as w is reduced, reaching 0 for w=0.Therefore, this circuit performs as a high-pass filter.

for taking out FREQUENCY RESPONSE of these networks you can simply apply VOLTAGE DIVIDER RULE to their frequency domain equivalent network to find its OUTPUT VOLTAGE Vo and the results are shown in table.