Draw circuit diagram of a basic RC band-pass filter. Sketch its frequency response clearly showing the expressions for cut-off frequencies.

The filter which blocks lower limit frequency and the higher limit frequency and allow only the frequency below the limits is called as band pass filter.

Using R C band pass filter is designed. To avoid loading on second filter the Critical frequency of high pass filter is low critical frequency and for low pass filter it is high critical frequency. These is loading effect of constant 'r'. And 'r' is ratio of the high pass filter resistance to the low pass filter resistance.

$$r = \frac{R_H}{R_L}$$

Therefore, The magnitude of output voltage to input voltage is -

$$\frac{V_{out}}{V_{in}} = \frac{f_{H}f}{\sqrt{(f^2-f_{H}f_{L})^2 + [f_{L}+(1+r)f_{H}]^2f^2}}$$

The critical frequency are given as follows :-

$$f_{H} = \frac{1}{2\pi R_{L} C_{L}}$$ and,

$$f_{L} = \frac{1}{2\pi R_{H} C_{H}}$$