Experiment 10 – Filter Design Project

Fall 2009

1. Design Project – The final project is a design of a non-inverting higher order active filter. You will design and calculate (using the equations in Chapter 11 of Sedra1 and Matlab (Tutorial)) the amplitude/frequency response (Bode Plot) for a Butterworth and Chebyshev filter that exceeds the specifications given below. Then select the better (in this case fewer op-amps) of the 2 designs and simulate it using PSpice to verify that the Bode Plot matches the Matlab calculations. Then you will build it in the lab using the solderless breadboards and the LF347 op amps and measure the amplitude/frequency response of the circuit and verify that it matches the Bode Plot from Matlab. At the end of the project you should have 3 Bode Plots that all match.

Filter Specifications as described in Sedra/Smith, “Microelectronic Circuits, 4th Edition”, Figure 11.3
DC Gain / 20 dB
Amax / 3 dB
Amin / 60 dB
Group / 1 / 2 / 3
Fp (KHz) / 5 / 7 / 9
Fs (KHz) / 37 / 50 / 60

Fill out the table below to compare the Amplitude Response measurements.

Amplitude (dB)
Butterworth / Chebyshev
Frequency / Sedra Eq. 11.11 / Matlab / Sedra Eq. 11.18,11.19 / Matlab / PSpice / Hardware
Fp/10
Fp
(Fp+Fs)/2
Fs
1. Design Steps:
2. Transfer Function Design - Using the equations from Sedra, define the filter transfer functions (Butterworth and Chebyshev) for the lowest order filter that exceeds the specifications. By exceeds, it is meant that the attenuation at Fs is at least 60 dB. Use Matlab to obtain the Bode plot (magnitude versus frequency) from 1Hz to 1MHz for both filters and verify that your filters meet the specifications. Check the plot against equations 11.11, 11.18 and 11.19 in Sedra at the frequencies in the above table to verify that the Bode Plot is correct. Plot the Chebyshev and Butterworth responses on the same graph and compare them. Also using Matlab, plot the step responses. Present these results to the instructor. Make sure that all plots are well labeled!
3. Schematic Diagram – Using OrCAD (Download,Tutorial), draw the circuit to implement the “better” of the 2 designs. Simulate this circuit using PSpice (Tutorial here) (AC Sweep and Step Response) and compare to your Matlab results for your selected design. Make sure to use the “OPAMP” model from the Analog library for the simulations.
4. Circuit Construction and Test - Construct the filter circuit using the breadboards and retain them in your locker in Bryan 306. Some prototyping may be necessary to understand the best way to connect components. Once your circuit is complete and seems to be operating, do preliminary testing and compare results to those obtained using PSpice. Once you have satisfactorily debugged your circuit, test it carefully and record enough data to make a complete Bode plot and prove that it meets the requirements defined above. Obtain data comparable to that obtained in steps (a) and (b). Measure the step response for a 1volt input.
5. Filter Demonstration. Demonstrate the filter to the class.
6. Report. Submit a report documenting the design process and test results. Include a list of materials (resistors, capacitors, and operational amplifiers) and an estimated cost per circuit for a quantity of 1000 filters. Include printed circuit board cost, but not labor costs.

Due Dates:

Report and prototype model are due 12/03/08.

References:

1. Adel S. Sedra and Kenneth C. Smith, MicroelectronicUniversity Press, New York, New York, 2004, 4th edition.