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ASSIGNMENT 2
SEE216 ANALOGUE AND DIGITAL ELECTRONICS
QUESTION 1
Consider the JFET circuit in Figure 1. The JFET has ???????? = 8 ???? and ??????(??????) = -7 ??.
Figure 1: JFET self-bias circuit
Compute the Q-point of the circuit (?????? and ????????). [8 marks]
QUESTION 2
You are attempting to implement a NOR gate by using the BJT circuit shown in Figure 2. Note that the two BJTs are identical.
Figure 2: NOR gate implementation
There are two operational requirements that you need to achieve:
• The required output voltage thresholds are: ?????? = 2.4 and ?????? = 0.4.
• The current load at the base cannot exceed a certain value, i.e. ???? = ????(??????) = 100 ????.
Given that:
• ??????(??????) = 0.2 ??,
• ?????? = 50,
• the input voltage (for both inputs at A and B) is ?????? = 1.5 ?? for HIGH level and ?????? = 0 ?? for LOW level, choose the values for ???? and ???? from the list of standardised resistor values in Table 3 (Appendix A) to satisfy the operational requirements of the NOR gate. In your workings, clearly show that the chosen resistor values will be able to satisfy the operational requirements for each case (i.e. each row) presented in the truth table in Table 1 below. [12 marks]
Table 1: NOR truth table
A B F
LOW LOW HIGH
LOW HIGH LOW
HIGH LOW LOW
HIGH HIGH LOW
Example: When we consider the first row of Table 1, we have ???? = ???? = 0 ?? = ??????. Thus, you have to show that ???????? 2.4 ?? = ??????. Similarly, when we consider the second row of Table 1, you have to show that
???????? 0.4 ?? = ?????? given that ???? = 0 ?? and ???? = 1.5 ?? = ??????.
Hint no.1: The output voltage thresholds are the upperlower bounds for the voltage value, meaning the actual value of the output voltage can be lower (for LOW output) or higher (for HIGH output) than the corresponding threshold values.
Hint no.2: Operate the BJTs either at cut-off or saturation.
QUESTION 3
Consider the common emitter small signal amplifier in Figure 3.
Figure 3: Common emitter small signal amplifier
You are attempting to design the amplifier to satisfy some pre-specified operational requirements. The operational requirements and the given parameters are shown in Table 2. Please use the dataset corresponding to the last digit of your student ID number.
Example: If your student ID number is 463184250, then please use Dataset 0. If your student ID number is 123456789, then please use Dataset 9.
Table 2: Datasets of the operational requirements and the given parameters.
Dataset no. 0 1 2 3 4 5 6 7 8 9
Given parameters
?????? [??] 8 14 15 15 15 12 9 9 11 9
?????? 90 90 100 150 80 80 150 120 150 140
?????? 50 100 50 90 90 90 60 100 60 90
???? [??] 10 70 80 10 50 30 90 70 30 40
???? [????] 10 7 8 7 7 9 9 8 7 9
?????? [????] 30 30 5 5 25 15 15 25 20 10
?????? [????] 5 15 5 5 10 5 5 10 20 5
Operating requirements
???????? [??] 0.5 ?????? ± 0.5
Min operating freq. range [??????] 4 1 2 2 2 4 5 3 1 3
Max operating freq. range [??????] 6 3 5 6 4 7 7 4 2 6
Your task is to choose the values for ??1, ??2, ????, ????1, ????2, ??1, ??2, and ??3 such that the operating requirements are satisfied. The values of the resistors and capacitors have to be selected from the list of standardised values shown in Table 3 (Appendix A) and Table 4 (Appendix B), respectively.
Once you have selected the resistor and capacitor values, please do the following to demonstrate that you have achieved the operating requirements.
A. Using the Thevenin method, compute the Q-point (?????? and ????????). [4 marks]
B. Compute the overall AC voltage gain [6 marks]
C. Compute the three lower cut-off frequencies. [5 marks]
D. Compute the two upper cut-off frequencies. [5 marks]
Hint no.1: The operating frequency range are thresholds, meaning that you have satisfied the requirement as long as this range is fully contained within the passband of the amplifier.
Hint no.2: Choosing the values for the resistors and capacitors can be done via trial-and-error. But, try to think of a faster way to do the trial-and-error! ?
Hint no.3: You can remove ????1 if need be.
Optional challenge no.1: Besides meeting the operating requirements, try to maximise the voltage gain!
Optional challenge no.2: Try to achieve a passband that is as close as possible to the operating frequency range!
APPENDIX A RESISTOR VALUES
Table 3: Standardised resistor values.
O kO
10 100 1.0 10 100
11 110 1.1 11 110
12 120 1.2 12 120
13 130 1.3 13 130
15 150 1.5 15 150
16 160 1.6 16 160
18 180 1.8 18 180
20 200 2.0 20 200
22 220 2.2 22 220
24 240 2.4 24 240
27 270 2.7 27 270
30 300 3.0 30 300
33 330 3.3 33 330
36 360 3.6 36 360
39 390 3.9 39 390
43 430 4.3 43 430
47 470 4.7 47 470
51 510 5.1 51 510
56 560 5.6 56 560
62 620 6.2 62 620
68 680 6.8 68 680
75 750 7.5 75 750
82 820 8.2 82 820
91 910 9.1 91 910
APPENDIX B CAPACITOR VALUES
Table 4: Standardised capacitor values.
pF µF
1.0 10 100 1000 0.01 0.1 1.0 10 100 1000
1.1 11 110 1100
1.2 12 120 1200
1.3 13 130 1300
1.5 15 150 1500 0.015 0.15 1.5 15 150 1500
1.6 16 160 1600
1.8 18 180 1800
2.0 20 200 2000
2.2 22 220 2200 0.022 0.22 2.2 22 220 2200
2.4 24 240 2400
2.7 27 270 2700
3.0 30 300 3000
3.3 33 330 3300 0.033 0.33 3.3 33 330 3300
3.6 36 360 3600
3.9 39 390 3900
4.3 43 430 4300
4.7 47 470 4700 0.047 0.47 4.7 47 470 4700
5.1 51 510 5100
5.6 56 560 5600
6.2 62 620 6200
6.8 68 680 6800 0.068 0.68 6.8 68 680 6800
7.5 75 750 7500
8.2 82 820 8200
9.1 91 910 9100