Examen ET1205-D1 Elektronische Circuits deel 1, 5 April 2011, 9-12 uur Het is geen open boek tentamen. Wel mag gebruik gemaakt worden van een A4- tje met eigen aantekeningen. Indien, bij het multiple choice gedeelte, een antwoord dat U heeft uitgerekend niet voorkomt, kiest U de waarde die het dichts bij Uw antwoord komt. Bij de open vragen moet altijd een berekening of motivatie worden gegeven. Een woordenboek is eventueel ook toegestaan. Er zijn 20 multiple choice vragen (A) en 2 open vragen (B en C). Bij (A) kunt U 5 punten behalen, bij (B) 2 punten en bij (C) 3 punten. Wilt U de antwoorden van de multiple choice vragen op uw antwoordbladen invullen, en vergeet niet uw naam en studienummer te vermelden.
A Multiple Choice 1) What form of waveform is shown here? a) a binary signal b) An analogue signal c) A multi-valued digital. d) A digital signal 2) Consider the following filter circuit. At high frequencies: a) ÜÜ is small and the voltage gain is 0 b) (JÜ is large and the voltage gain is 0 c) 03 is small and the voltage gain is 1 d) O) is large and the voltage gain is 1 3) Which of the following correctly described the characteristics of a good amplifier, if used for current amplification? a) A very low input resistance and a very high output resistance. b) A very low input resistance and a very low output resistance. c) A very high input resistance and a very high output resistance. d) A very high input resistance and a very low output resistance.
4) The figure below shows a negative feedback system. The gain of A is 10 and the gain of B is 1, What is the overall gain of this amplifier? a) 0.9 b) l c) 1.1 d) 9 5) Under what conditions does the gain of a feedback system approximate to 1/6? a) The loop gain AB«1. b) The forward path gain A»1. c) The feedback path gain B»1. d) The loop gain AB»1. 6) Given the Bode diagram below, it shows the bandwidth with and without feedback. What is indicated by (a) and what by (b)? Gain 4 (db) (a) (b) / -> Frequency a) (a) = bandwidth without feedback, and (b) = open-loop gain b) (a) = bandwidth without feedback, and (b) = closed-loop gain c) (a) = bandwidth with feedback, and (b) = open-loop gain d) (a) = bandwidth with feedback, and (b) = closed-loop gain
7) What is the output resistance of this amplifier? a) R1 + R2 b) R1//R2 c) It is approximately equal to the output resistance of the operational amplifier d) It is much lower that the output resistance of the operational amplifier 8) For an operational amplifier the graph below is given. What bandwidth can be attained with this operational amplifier when it is used to make a voltage amplifier with a gain of 1000? Voltage gain 10'* 10' 10* 10^ 10^ 10 1 -L _L _L _L 10 100 Ik 10k 100k IM lom Frequency (Hz) a) approximately 10 Hz b) approximately 100 Hz c) approximately 1 khz d) approximately 10 khz
9) The figure below shows the characteristics of a MOSFET. When we want to use this transistor as a voltage controlled resistor, in which region should it be used? a) Region (a) b) Region (b) c) Exactly between region (a) and (b); close to the dotted line d) It cannot be used for that purpose 10) Estimate the peak ripple voltage in the following arrangement. a) 10 mv b) 25 mv c) 50 mv d) 100 mv 11) What is a typical conduction voltage for a silicon diode? a) 0.25 V b) 0.5 V c) 0.7 V d) 1.1 V
12) What form of FET is shown here? Drain t;hannel P Gare C " H-type ""^ gate region Source a) A;7-channel MOSFET. b) A jo-channel JFET c) An 77-channel MOSFET d) An ;7-channel JFET 13) Determine the cut-off frequency of the following circuit. 0 fyjo{10v) IkQ <> ^:s-.s(o V) a) b) c) d) 0.63 Hz 1.6 Hz 3.6 Hz 10 Hz
14) What are the characteristics of the following circuit? o 0 ' v.s-((iv) (I)) An cnlninccmciu MOSI'I'/I" a) A voltage gain of 1, a low input resistance and a high output resistance. b) A voltage gain of 1, a high input resistance and a low output resistance. c) A high voltage gain, a high input resistance and a low output resistance. d) A high voltage gain, a low input resistance and a high output resistance. 15) Which of the following expressions represents the transconductance of a bipolar transistor? a) IC/VBE b) /C//B c) d/c/dfbe d) d/c/d/b
16) Determine ttie quiescent collector current of the following circuit, given that the /IFE of the transistor is 200. a) 1.3 ma b) 1.4 ma c) 4.2 ma d) 4.4 ma 17) Determine the quiescent output voltage of the following circuit. Vrn= 12V C V; a) -1.2 V b) 5.2 V c) 7.3 V d) 7.5 V
18) What is the small-signal voltage gain of the circuit? a) 2.83 b) 2.56 c) -2.2 d) -1.83 19) Wat zijn de elementen van de G-matrix van de volgende tweepoort? + R I + a) y\\ = R; yu = R; y2i=r; yi2 = R b) yn = ^; yn=-r\ y2\=-r; yi2 = R c) yn = R''\ yn = R'^; y2i = R'^; y22 = R' d) yii = i?''; yi2=-i?"'; y2i = -R'^; y22 = R'
20) Wat zijn de elementen van de ketting matrix van de volgende transactor? (in volgorde kn, ki2, k2i, k22) a) yt'\ O, O, O b) 0,yt-',0,0 c) O, O, y,-^ O d) 0, O, 0,Yt"' B Open vraag 1: Consider the following amplifier circuit. The amplifier has a voltage gain of 10, an input resistance of 1 kq and an output resistance of 10 Q. The amphfier is connected to a transducer that produces a voltage of 2 V and has an output resistance of 100 Q, and to a load of 50 Q. Source Amplifier Load o O 1 > k > i 4 O %n ^4 O RL! 50 Q I a) Calculate the output voltage of the amplifier (that is, the voltage across the load resistance)? b) Calculate the voltage gain ofthe amplifier.
C Open vraag 2: Design an amplifier circuit based on a 741 op-amp to amplify the signal of the following sensor. The signal coming from this sensor is a vohage varying in time. The sensor has a resistance of 1 kfl. The amplifier design must be such that the resistance of the sensor does not have a significant contribution (<10'^) to the overall gain. The figure below shows the model that can be used for the sensor. The amphfier consists of a 741 operational amplifier (op-amp) and the unloaded voltage gain ofthe amphfier must be 25, in absolute values. Given is that the openloop gain ofthe 741 is typically 2x10^; the output resistance of a 741 is typically about 75 Q.; and the input resistance of a 741 is typically about 2 MÜ.. a) Design the amplifier circuit. b) Show by calculation that the resistance of the sensor does not significantly contribute to the overall gain ofthe amplifier (assume the op-amp to be ideal). c) Calculate the input- and output resistance of the amplifier circuit.
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