EE3B1 Exam Revision Past papers New course, but almost identical syllabus to EEM3A, paper 1, section 2 ( ) Before 2001, more and more material may have changed New format There are now Four questions, of which Three must be answered

Revision Lectures / Tutorials Two sessions Power Amplifiers Low Noise High Frequency Amplifiers Active Filters

Revision What should you be expected to do in a typical exam question ? Understanding of basic principles. Ability to perform simple circuit analysis and/or design. Applying skills to unfamiliar problems.

Mock Paper 1. Figure 1 shows a power amplifier circuit. Throughout this question you should assume that for all the transistors,  = 200 and V BE = 0.7 V. Also, assume that the quiescent level of VIN is set such that V OUT = 0 V in the quiescent state.

(a)What class of power amplifier is this circuit? Class AB (b)What is the name of the configuration formed by Q4, Q5 and the 7 k  resistor Current Mirror (c)Calculate the collector current of Q4.

(d)What is the name of the configuration formed by Q 3 and the 4 k  and 3.5 k  resistors? V BE Multiplier (e)Calculate the potential difference between the bases of Q 1 and Q 2.

(f)Calculate the quiescent potential difference between the emitter of Q 1 and V OUT. Using your answer, also calculate the quiescent emitter current of Q 1.

(g)What is the purpose of transistor Q 6 ? Short circuit protection (h)In operation, assuming a sinusoidal input of amplitude A, calculate: i.An expression for the load power dissipated by the 64  load resistor.

ii.An expression for the total power drawn from the supplies.

iii.An expression for the efficiency of the amplifier as a function of A.

iv.The input level, A, when the power that must be dissipated by the transistors is at its peak. v.The peak power dissipation.

2.The general form of a normalised 2nd order low-pass filter is: (a)What is the value, , known as? Damping ratio (b)What does a value of  <1/  2 imply? Under-damped filter, resonant peak

The transfer function of a 6th order normalised Butterworth filter is: where the factors H1, H2 and H3 represent the three 2nd order sections required to build the filter using synthesis by sections. (c)Calculate the value of  for each of the factors H1, H2 and H3.

(d)Identify whether each of the three sections is under-damped, over-damped or critically damped. Critically damped Under-damped Over-damped

(e)At the cut-off frequency,  = 1 rad/s, what is the gain of each of the 2nd order sections? (f)To achieve the largest undistorted input voltage range, which of the three sections should be arranged to come first? Least resonant (most damped) section first: H 3

(g)Using the Sallen and Key circuit shown in figure 2, design a 6th order low-pass Butterworth filter for a cut-off frequency of 2000 rad/s using only 5 k  resistors. For all sections:

In order: Remember to draw the finished circuit with all component values