ESP1104 Introduction to Electronic Systems Khursheed
Tutorial 3
1) An RC filter is inserted into a circuit as shown in the figure below, where RS = 50Ω, R = 200 Ω, RL = 500 Ω and C = 10 μF.
Use Thevenin’s theorem to calculate expressions for the amplitude and phase of the transfer function of the circuit, express it in a form that can be compared with the ideal filter response (that does not take into account RS and RL). What kind of filter is it? How does its cut-off frequency differ from the ideal RC case? In what circumstances would you expect the ideal filter approximation to the circuit to be very inaccurate and why might this be important to understand in real situations?
2) It is common practice to filter out noise that may be present at the output of a
Wheatstone bridge used with strain gauges. Assume that a 350 Ω resistor is used in each leg of the Wheatstone bridge powered by a DC source, and that the signal from the strain gauge has a frequency of 30 Hz. Design a simple filter to eliminate noise that has
frequencies well above 300 Hz.
RL C
R RS
Filter Load
Source VS(ω)
VL(ω)
3) Derive the transfer function frequency response of the circuit shown below. Explain how the circuit can be used to filter out interference effects that have a particular frequency. If, R = 100 Ω, L = 100 mH, what does the value of C need to be if it is to filter out interference caused by mains power lines (240 RMS volts, 50 Hz)?
Suggest how you might modify the circuit above to use the capacitor and inductor in parallel in order to achieve the same type of filtering action. Would you need to modify the capacitor/inductor values?
VS(ω)
R
L C
V0(ω)
