1. ELEC 202 Circuit Analysis II
FREQUENCY RESPONSE
ELEC 202 Circuit Analysis II

2. Introduction
The frequency response of a circuit is the variation in its behavior due to the change in signal frequency.
Measured in terms of the variation of the gain and phase as a function of frequency
Vary the frequency of the input signal source (i.e. sinusoid) while keeping its amplitude constant
Important in filter design

3. Definition
For a circuit with a sinusoidal input source, its frequency response is defined as the ratio of its phasor output to its phasor input, expressed as a function of frequency.

4. Types of Frequency Response

5. Characteristics
Typically expressed as an irreducible ratio of two polynomials in frequency (i.e., the common numerator and denominator factors have canceled, reducing the ratio to the lowest terms)
When working with , temporarily replace with s to avoid complex algebra 5

6. Characteristics (Cont’d)
Roots of the numerator polynomial
are called the zeros of
Roots of the denominator polynomial
are called the poles of 6

7. The Decibel Scale
The use of a logarithmic scale to express gain (either power, voltage or current)
The 10log is used for power, while 20log is used either for voltage or current.
The two quantities in the ratio must be of the same type. 7

8. Example For the RC circuit shown, determine and
sketch its frequency response.

9. Magnitude Response
Phase response

10. Example For the RL circuit shown, determine and
sketch its frequency response.

11. Magnitude Response
Phase response

12. Example For the circuit shown, determine the gain
and its poles and zeros.

13. Example For the circuit shown, determine its transfer
impedance and obtain its poles and zeros.