Partner
Experiment
Second-order
Filters
Purpose.
The
purpose of this experiment is to study second-order, active, low-pass filters.
Compare the three designs and summarize your
results.
Filter #1
Design a Sallen-Key filter where the Q is determined by the gain of the amplifier and the frequency determining R’s and C’s are equal. Analyze* this circuit in your notebook. Do not build this circuit but do a Monte-Carlo simulation with 5% resistors and 20% capacitor to show that the component sensitivity is bad for a Q as low as 2. You might check higher and lower Q’s if you have time.
There is about a 50/50 chance that this circuit will oscillate if you build it because the Q is so high. Be sure you understand the component sensitivity analysis in the following link.
*"Analyze" means determine the s-domain transfer
function, Vout/Vin, or a frequency response (Bode plot) and from that determine the pass-band gain, corner frequency
and Q of the circuit.
Filter #2
Design a filter to meet the above specifications using an MF-10 switched-capacitor filter. Simulation is not required. Note the quantization steps on the output and the aliasing that will occur for any signal frequencies that are near the clock frequency. The circuit for the MF-10 is equivalent to a state-variable circuit (you are not required to build the state variable circuit in addition to the switched-capacitor implementation, you may if you choose) using three or more op amps. Data sheets and application notes for the MF-10 are on the web. Read the datasheet carefully with particular attention to pinouts.
http://pdfserv.maxim-ic.com/arpdf/MF10.pdf
Filter #3
Analyze, Design, simulate, build and test a
Sallen-Key filter with a gain of ONE and control the Q and frequency with the
input R’s and C’s. This circuit is not as sensitive to component tolerance
as filter #1. Show this with a
Monte-Carlo simulation with the same component tolerances as filter #1.
