Act.Filts.V4

# Act.Filts.V4 - L 302-5.V4 Drexel University Electrical and...

This preview shows pages 1–4. Sign up to view the full content.

L302-5.V4 5-1 Drexel University Electrical and Computer Engr. Dept. Electrical Engineering Laboratory II, ECEL 302 E. L. Gerber ACTIVE FILTER DESIGN (X2) Object The object of this experiment is to learn what active filters are and to learn a basic active filter design procedure. Also, you will experience the process of constructing and evaluating an active filter design. Introduction Active filters consist of op-amps and various RC circuit configurations designed to produce a specific voltage gain frequency response. Inductors are ruled out. In this experiment we will introduce a basic design procedure based on the y-parameters of RC networks. Only one inverting op-amp will be utilized and two RC networks. One network is the input network the other is the feedback. A wide variety of transfer functions can be obtained using this procedure. Theory I - Four-terminal Network Parameters: Any linear four-terminal network can be represented by four quantities called parameters. The diagram in Fig. 1 shows the four terminal variables V 1 , V 2 , I 1 , and I 2 defined in the parameter equations. Only two equations are needed to completely define the network. One set of equations is the y-parameter equations given below. They relate the terminal currents in terms of the terminal voltages. These four parameters are constants of a particular network, and are called the admittance parameters. Each parameter can be determined from one of the two equations when V 1 or V 2 is zero. See Appendix C in Irwin.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
L302-5.V4 5-2 I 1 = y 11 V 1 + y 12 V 2 I 2 = y 21 V 1 + y 22 V 2 Figure 1: Four Terminal Variables For example, the y 11 term can be found from the first equation as I 1 /V 1 when V 2 = 0. The four y-parameters are found by shorting either the input or the output terminals and evaluating the appropriate I/V ratio. Several y-parameters are calculated for a simple circuit in Fig. 4. II- Op-amp Inverting Amplifier: A typical configuration for an active filter is shown in Fig. 2. The networks A and B represent passive networks and consist of RC elements only. Circuit A is the input circuit and B is the feedback. By considering networks A and B each as a four-terminal network we can write the following four equations for the two circuits. Note all voltages in the circuit are referenced to ground. Figure 2: An op-amp active filter configuration .
L302-5.V4 5-3 a) Network A I 1 = y 11a V 1 + y 12a V 2 (1) I 2 = y 21a V 1 + y 22a V 2 (2) b) Network B I 3 = y 11b V 3 + y 12b V 0 (3) I 4 = y 21b V 3 + y 22b V 0 (4) The parameter y 11a is the input admittance of network A with the output terminals shorted (V 2 = 0). Parameter y 12a is called the transfer admittance (I 1 /V 2 ) with the input terminals shorted (V 1 = 0). Since circuits A and B are passive circuits, y 21 is always equal to y 12 . Finally, y 22 is the admittance at the output terminals (I 2 /V 2 ) with the input terminals shorted (V 1 = 0). In Fig. 2, if the input impedance of the op-amp is very high (a good assumption), I

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

## This document was uploaded on 09/25/2011.

### Page1 / 13

Act.Filts.V4 - L 302-5.V4 Drexel University Electrical and...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online