Give design procedure of first order HPF.
1 Answer

High pass filters are often formed simply by interchanging frequency determining resistors and capacitors in low pass filters. That is, a first order high pass filter is formed from a first order low pass type by interchanging components R and C. Figure 1 shows the first order high pass filter with a low cutoff frequency of $f_L$. This is the frequency at which the magnitude of the gain is 0.707 times its passband value, all frequencies higher than $f_L$ are passband frequency, with the highest frequency determined by the closed loop bandwidth of the op-amp.

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A first order HPF (High Pass Filter) can be designed by implementing the following steps :

  1. Choose a value of low cutoff frequency $f_L$.

  2. Select a value of C less than or equal to 1µF. Mylar or tantalum capacitors are recommended for better performance.

  3. Calculate the value of R using, $$R = \frac{1}{2πf_LC}$$

  4. Finally, select values of $R_1$ and $R_F$ dependent of the desired passband gain $A_F$ using,

$$A_F = 1 + \frac{R_F}{R_1}$$

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