Download Active Filters - Electrical and Computer Engineering - Lab Handouts and more Lecture notes Electrical Engineering in PDF only on Docsity!
Electrical & Computer Engineering
ECE-E421: Advanced Electronics I
Lab#3: Active Filters
This lab consists of designing and testing 3 types of active filters and one cascaded filter. The filter types are:
High pass filter implemented with a single feedback operational amplifier configuration.
Band pass filter, implemented with a multiple feedback, operational amplifier configuration. (Delyiannis-Friend Circuit).
Low pass filter, implemented with a controlled-source configuration. (Sallen and Key Circuit).
Cascaded band pass filter with twp identical filter stages of the single feedback, operational amplifier configuration.
For all the filters to be designed in this lab, use the LM741C operational amplifier.
Note: In order to minimize the effect of the bias current, always match the DC-impedance to ground of the two inputs to the op amp (inverting and non-inverting inputs)
Preparations
1. Design a high pass filter implemented with a single feedback, operational amplifier configuration. The RC network to be used is given in Figure 1.
The transfer function for a high pass filter with complex conjugate poles has the following form:
Use the following design data for the high pass filter:
Pass band gain = 16.7 dB ; ζ = 0.5 ; fn = 250Hz
Write the expression for H(s) and sketch the magnitude Bode Plot of H(s). Determine and show the filter configuration, and express the transfer function, H(s), in form of the resistors and capacitors. You should produce a design using only the following component values:
Resistors: 12K and 47K Capacitors: 27 nF
2. Design a band pass filter, implemented with a multiple feedback, infinite gain op amp configuration. This circuit is described in Van Valkenburg as the Delyiannis-Friend Circuit on pp. 203-207, and the particular version to be used is shown in Figure 2.
Figure 2
Use the following design procedure:
Figure 4
The transfer function for a band-pass filter is given in the following expression:
Use the following data for the design:
Write the expression of H(s) in terms of R1, R2, RA, RB, C1 and C2 and sketch the Bode-plot. Design the filter so as to have minimum sensitivity to capacity drift or deviation starting from assigning R1=R2 and C1=C2=33nF. Refer to the supplementary materials for sensitivity calculation. You are allowed to use only 12K and 47K resistances. To match the DC impedance use the controlled source circuit by selecting RA || RB = R1 + R2. Show that this selection minimizes the input bias current of the op-amp.
BONUS PART *** ( + 20%) Design a cascade band-pass filter with two identical filter stages of the single feedback operational amplifier configuration. The circuit to be used is given in Figure 5, with R1=R3.
Figure 5
The desired Bode-plot of the circuit is given in Figure 6.
Figure 6
Note that the pole locations of a cascaded filter with real poles are not identical to the breakpoint frequencies of the magnitude Bode plot. To determine the poles, you should use:
