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Inverting and Noninverting OpAmp Voltage Amplifier Circuits
41 questions By Tony R. Kuphaldt
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Question 13 of 41
Calculate the necessary resistor value (R1) in this circuit to give it a voltage gain of 10.5:
Reveal answerR1 = 76.95 kΩ
Notes:Ask your students how they solved this problem, especially since it is fairly safe to say that they didn’t find the equation directly solving for R1 in any book. Algebraic manipulation is necessary to take the standard voltage gain equation and put it into a form suitable for use answering this question.
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Question 14 of 41
Predict how the operation of this operational amplifier circuit will be affected as a result of the following faults. Consider each fault independently (i.e. one at a time, no multiple faults):
- Resistor R1 fails open:
- Solder bridge (short) across resistor R1:
- Resistor R2 fails open:
- Solder bridge (short) across resistor R2:
- Broken wire between R1/R2 junction and inverting opamp input:
For each of these conditions, explain why the resulting effects will occur.
Reveal answer- Resistor R1 fails open: Output saturates positive.
- Solder bridge (short) across resistor R1: Vout = Vin.
- Resistor R2 fails open: Vout = Vin.
- Solder bridge (short) across resistor R2: Output saturates positive.
- Broken wire between R1/R2 junction and inverting opamp input: Output voltage unpredictable.
Notes:The purpose of this question is to approach the domain of circuit troubleshooting from a perspective of knowing what the fault is, rather than only knowing what the symptoms are. Although this is not necessarily a realistic perspective, it helps students build the foundational knowledge necessary to diagnose a faulted circuit from empirical data. Questions such as this should be followed (eventually) by other questions asking students to identify likely faults based on measurements.
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Question 15 of 41
Calculate the voltage gain for each stage of this amplifier circuit (both as a ratio and in units of decibels), then calculate the overall voltage gain:
Reveal answer- Stage 1:
- AV = 4.3 = 12.669 dB
- Stage 2:
- AV = 6.745 = 16.579 dB
- Overall:
- AV = 29.002 = 29.249 dB
Notes:Not only does this question review calculation of voltage gain for inverting amplifier circuits, but it also reviews decibel calculations (for both single and multi-stage amplifiers). Discuss how the decibel figures for each stage add to equal the total decibel gain, whereas the ratios multiply.
