Question

Active Low-pass and High-pass Filters for Crossover Circuitry (PSPICE)

B. Active Low-pass and High-pass Filters for Crossover Circuitry (40 pts) Design a first order active high-pass filter with cut-off frequency of 1 kHz & gain 20dB. Design a first order active low-pass filter with cut-off frequency of 1 kHz & gain 20dB. Plot the magnitude and phase responses of the active high-pass and low-pass filters you have designed using PSpice (Use UA741 Op amp and +12V dual supply). Connect your active low-pass and high-pass filters as shown in Fig. 1-b. Assume that Tweeter speaker and Woofer speaker have resistance of 8 and 16 respectively. Plot the magnitude and phase responses of the circuit by taking the output from Tweeter speaker and Woofer speaker respectively for parallel crossover circuit using PSpice. Calculate the two transfer functions Voltweeter)/Vinput and Volwoofer)/Vinput for the circuit given in Fig. 1-b. Sketch the magnitude and phase responses of the parallel crossover circuit and check your results using PSpice.

• Design a first order active high-pass filter with cut-off frequency of 1 kHz & gain 20dB.
• Design a first order active low-pass filter with cut-off frequency of 1 kHz & gain 20dB.
• Plot the magnitude and phase responses of the active high-pass and low-pass filters you have designed using PSpice (Use UA741 Op amp and ±12V dual supply).
• Connect your active low-pass and high-pass filters as shown in Fig. 1-b. Assume that Tweeter speaker and Woofer speaker have resistance of 8 Ω and 16 Ω respectively. Plot the magnitude and phase responses of the circuit by taking the output from Tweeter speaker and Woofer speaker respectively for parallel crossover circuit using PSpice.
• Calculate the two transfer functions Vo(tweeter)/Vinput and Vo(woofer)/Vinputfor the circuit given in Fig. 1-b. Sketch the magnitude and phase responses of the parallel crossover circuit and check your results using PSpice.

Answer 1

Question (a)

The circuit diagram of a first order active low pass filter is shown below

The Pass Band Gain is given by

The Cut off Frequency

We need the pass band gain to be 20 dB

So

So

Let us take

Then

The higher cut off frequency of a first order low pass filter is given by

Now the cut off frequency required is 1 kHz

So

Let us take

Then

So the circuit is

Question (b)

The circuit diagram of a first order active high pass filter is shown below

The Pass Band Gain is given by

The Cut off Frequency

We need the pass band gain to be 20 dB

So

So

Let us take

Then

The lower cut off frequency of a first order low pass filter is given by

Now the cut off frequency required is 1 kHz

So

Let us take

Then

So the circuit is

Question (c)

Simulation of Low Pass Filter in Pspice

The Circuit diagram is wired as follows

The simulation profile

After running we get

The plot shows the variation of output voltage (green) as frequecny is increased. The input is a constant at 1V shown by the red line. We can see that the pass band gain is 10V/1V = 10 as we had designed.

The gain in dB Vs frequency plot can be plotted as follows

Now we get gain in dB plot as follows

We can see that the pass band gain is 20dB as we wanted

The cut off frequency is marked

We can see that it is 998.34370 Hz

For the HIGH PASS FILTER

Gain in dB

We can see that the pass band gain in dB is 20 dB

Fig 1 b is not given.