Frequency Response

• Notice that A denotes the amplitude of the sinusoid at the output and $\phi$ denotes the phase.
• Notice that A and $\phi$ are functions of the frequency.
• The function A(f) is called the magnitude response of the system and $\phi(f)$ is the phase response.
• Together, they are referred to as the frequency response of the system.
• For the case RC=1, the magnitude response is shown below.
• The figure shows that low frequency (< 1 Hz) sinusoids result in sinusoids of amplitude approximately equal to 1.
• We say low frequencies are not attenuated.
• High frequency sinusoids, however, are attenuated considerably.
• This circuit constitutes a lowpass filter.

  

Figure 4.6: Magnitude Response of RC circuit (RC=1).