Filter Design Lab Instruments XBP2 IN OUT XSC1 Tektronix 1 2 3 4 T G P Figure 1 1. Lowpass filter 1.1. Design the 1 st order passive lowpass filter with the cut off frequency of 20 kHz. V1 2.8 Vpk 20kHz 0° R1 7.8kΩ 5% C1 1nF XSC1 Tektronix 1 2 3 4 T G P V2 Figure 2 Run the simulation and explain the relationship between V1 and V2. Use the Bode plotter to sketch the curve of voltage gain in dB and frequency (from 100 Hz to 1 MHz). Page 1 of 7 Cuong Ngo V1 2.8 Vpk 20kHz 0° R1 7.8kΩ C1 1nF V2 XBP1 IN OUT Figure 3 Make sure that the following settings are selected: Magnitude, Vertical (Log, F=0 dB, I= -40 dB), Horizontal (Log, F=1 MHz, I= 100 Hz). Figure 4 Observe the attenuation at the frequency of about 200 kHz (move the cursor). Figure 5 Use the Bode plotter to sketch the phase response. Note that Bode plotter is in Phase Mode and its vertical setting is linear. Page 2 of 7 Figure 6 1.2. Design the 1 st order active lowpass filter with the cut off frequency of 4 kHz, gain of 3 V1 1.4 Vpk 4kHz 0° R1 3.9kΩ 5% C1 10nF V2 U1 741 3 2 4 7 6 51 VCC 12V VEE -12V R2 10kΩ R3 22kΩ XSC1 Tektronix 1 2 3 4 T G P Figure 7 Find the gain of this circuit in dB and comment the following result. Figure 8 Page 3 of 7 1.3. Second order lowpass filter (Sallen-Key topolofy) The task is to design a second order Butterworth lowpass filter with the cut-off frequency of 3 kHz. V1 1.4 Vpk 3kHz 0° R2 4.9kΩ 5% C1 10nF V2 U1 741 3 2 4 7 6 51 VCC 12V VEE -12V XSC1 Tektronix 1 2 3 4 T G P R1 2.7kΩ 5% C2 22nF Figure 9 Sketch the input and output signal. Use the Bode plotter to verify the amplitude response and to observe the 40 dB/decade roll-off (in the case of 2 nd order lowpass filter). 2. Highpass filter 2.1. First order highpass filter: cut-off frequency fc=400 Hz. Verify the circuit in Figure 10. Page 4 of 7 V1 1.4 Vpk 400 Hz 0° R1 3.9kΩ 5% C1 100nF V2 XSC1 Tektronix 1 2 3 4 T G P Figure 10 Sketch the amplitude and phase response with the help of Figure 11 Figure 11 2.2. First order active highpass filter: fc=400 Hz. Page 5 of 7 V1 1.4 Vpk 400 Hz 0° R1 3.9kΩ 5% C1 100nF V2 U1 741 3 2 4 7 6 51 VCC 12V VEE -12V R2 10kΩ R3 22kΩ Figure 12 Compare the difference between the amplitude response of circuit in Figure 11 and of circuit in Figure 12. 3. Bandpass filter: passband from 400 Hz to 4 kHz V1 1.4 Vpk 400 Hz 0° R1 3.9kΩ 5% C1 100nF V2 U1 741 3 2 4 7 6 51 VCC 12V VEE -12V R2 10kΩ R3 22kΩ R4 3.9kΩ 5% C2 10nF V2 U2 741 3 2 4 7 6 51 VCC 12V VEE -12V R5 10kΩ R6 22kΩ XBP1 IN OUT Figure 13 Page 6 of 7 Comment on amplitude response Figure 14 Page 7 of 7