Unit 4 - Practice Quiz

1 What is the input impedance of an ideal operational amplifier?

2 What is the output impedance of an ideal op-amp?

3 What is the open-loop voltage gain of an ideal op-amp?

4 Which of the following describes the bandwidth of an ideal op-amp?

5 In the equivalent circuit of an op-amp, the output voltage is usually modeled as a dependent voltage source. What does this source depend on?

6 Where is the input impedance () placed in the equivalent circuit of an op-amp?

7 In the ideal voltage transfer curve of an op-amp, what happens when the differential input voltage is positive and slightly greater than zero?

8 What is the slope of the ideal voltage transfer curve in the linear region for an ideal op-amp?

9 What happens to a practical op-amp in open-loop configuration if a small DC differential input voltage is applied?

10 Which of the following applications typically uses an op-amp in an open-loop configuration?

11 What is the primary effect of introducing negative feedback in an op-amp circuit?

12 Which concept states that in a closed-loop op-amp circuit, the voltage difference between the inverting and non-inverting terminals is almost zero?

13 In the block diagram of a feedback amplifier, what does the 'mixer' network do?

14 In a feedback block diagram, the parameter typically represents:

15 Which basic op-amp circuit is a classic example of a voltage series feedback amplifier?

16 How does voltage series feedback affect the input and output impedances of an op-amp?

17 Which op-amp circuit represents a voltage shunt feedback amplifier?

18 What is the effect of voltage shunt feedback on the input impedance?

19 What is the main function of a differential amplifier?

20 What happens to the output of an ideal differential amplifier if the exact same voltage (common-mode voltage) is applied to both inputs?

21 An ideal op-amp is connected in a circuit with a feedback resistor. What happens to the input impedance seen by the source connected to the non-inverting terminal?

22 In the equivalent circuit of a practical op-amp, how is the output voltage modeled?

23 According to the ideal voltage transfer curve of an op-amp, if the differential input voltage is positive and extremely small, what is the output voltage?

24 In an open-loop inverting amplifier configuration, a 1 V sine wave is applied to the inverting input while the non-inverting input is grounded. If the open-loop gain is , what is the output?

25 Which of the following is a direct consequence of introducing negative feedback in an op-amp circuit?

26 In the block diagram of a feedback amplifier, if the feedback network samples the output voltage and mixes it in series with the input voltage, what is the feedback topology?

27 Calculate the closed-loop gain of a non-inverting op-amp (voltage-series feedback) if the feedback resistor and the input resistor .

28 In an inverting amplifier (voltage-shunt feedback), what is the effect of the virtual ground on the input impedance of the circuit as seen by the signal source?

29 A differential amplifier has a differential gain of 100 and a Common-Mode Rejection Ratio (CMRR) of 60 dB. What is its common-mode gain ()?

30 Which parameter allows an ideal op-amp to amplify DC signals without attenuation?

31 In the equivalent circuit of an op-amp, if the input resistance is very large but finite, what is the primary effect on the circuit when driven by a high-impedance source?

32 Why is an open-loop op-amp generally not used as a linear amplifier?

33 What is the primary reason the concept of 'virtual ground' is valid in an inverting amplifier with negative feedback?

34 If an op-amp feedback topology decreases both the input and output impedances, which topology is it?

35 In a voltage follower (a special case of voltage-series feedback), what are the values of and ?

36 Determine the output voltage of an inverting amplifier with , , and an input voltage .

37 A basic op-amp differential amplifier uses four resistors: and at the inverting input, and and at the non-inverting input. To ensure optimal common-mode rejection, what condition must the resistor values satisfy?

38 On the ideal voltage transfer curve, the region between and is a vertical line. What does this vertical line represent mathematically?

39 How does negative feedback affect the gain-bandwidth product (GBW) of an op-amp circuit?

40 In a feedback amplifier block diagram, the term represents the feedback factor. For a non-inverting amplifier with resistors and , what is the expression for ?

41 An ideal op-amp is connected in a circuit with infinite input impedance and zero output impedance. If a non-ideal parasitic capacitance is introduced at the inverting input node in a high-gain closed-loop configuration, what is the most significant consequence on the system dynamics?

42 In the equivalent circuit of a non-ideal op-amp, the finite open-loop gain is represented as a frequency-dependent voltage-controlled voltage source, . If this op-amp is used in a voltage series feedback topology with feedback factor , what is the exact expression for the closed-loop pole frequency ?

43 Consider an op-amp with an ideal voltage transfer curve bounded by . If a sinusoidal input is applied to an open-loop non-inverting configuration, and a small DC offset is present at the inverting terminal, what is the duty cycle of the resulting square wave output?

44 An op-amp operating in an open-loop configuration has a finite CMRR. If the differential gain is and the common-mode gain is , which of the following represents the total output voltage given inputs and at the non-inverting and inverting terminals respectively, considering edge case input combinations?

45 A negative feedback op-amp circuit exhibits a loop gain . To ensure a phase margin of exactly , a compensation capacitor is added that shifts the dominant pole. What must be the new dominant pole frequency approximately, assuming the second pole remains at rad/s?

46 In the general block diagram of a feedback amplifier, if the forward network has a strong reverse transmission and the feedback network has a forward transmission , what is the exact generalized expression for the closed-loop gain using Blackman's theorem or signal flow graph analysis?

47 A voltage series feedback amplifier is constructed using an op-amp with finite open-loop gain , input resistance , and output resistance . The feedback network consists of and (where ). What is the exact exact closed-loop output resistance without assuming ?

48 In a voltage shunt feedback topology (transimpedance amplifier) with feedback resistor , an op-amp has a finite gain-bandwidth product (GBW) and an input capacitance . To maximally flat the closed-loop frequency response (Butterworth response), a feedback capacitor is placed across . What is the required value of ?

49 A practical differential amplifier is built using a single op-amp with four resistors: and on the inverting side, and and on the non-inverting side. If resistor tolerances cause a worst-case mismatch of (where ), what is the approximate worst-case Common Mode Rejection Ratio (CMRR) of the circuit, assuming an ideal op-amp?

50 If an ideal op-amp is configured as a positive feedback Schmitt trigger with a reference voltage applied to the inverting terminal, and feedback resistors and at the non-inverting terminal, what are the exact upper () and lower () threshold voltages given saturation limits ?

51 In the AC small-signal equivalent circuit of an op-amp, the input stage generates a noise voltage spectral density and noise current spectral density . In a non-inverting amplifier with source resistance and feedback resistors (to ground) and (feedback), what is the total equivalent input noise voltage spectral density ?

52 An op-amp with an open-loop gain of and output saturation voltages of operates under open-loop conditions. A noisy DC signal is applied differentially. What is the maximum peak-to-peak amplitude of that will keep the op-amp strictly in the linear region of its voltage transfer curve?

53 A real op-amp with a slew rate of is driven by a step input in an open-loop configuration. Due to internal architecture, the input differential pair exhibits a maximum tail current and the compensation capacitor is . Which fundamental relationship correctly bounds the open-loop large-signal transient behavior?

54 In a negative feedback configuration, the sensitivity of the closed-loop gain to changes in the open-loop gain is given by . If , what must be the minimum feedback factor to guarantee that varies by no more than ?

55 When modeling an inverting op-amp configuration using the standard feedback block diagram, the forward gain and feedback factor are defined to match two-port network parameters. For an op-amp with gain and feedback resistor and input resistor , what is the correct block diagram parameter (feedback ratio) if ?

56 A voltage series feedback circuit uses an op-amp with an open-loop gain that has two poles: rad/s and rad/s. If the low-frequency loop gain is , what is the maximum value of to prevent the system from exhibiting an underdamped step response (i.e., to maintain a damping factor )?

57 In a voltage shunt feedback topology acting as a transimpedance amplifier, the source is a photodiode modeled as a current source in parallel with a large capacitance . The op-amp has an input resistance , open loop gain , and feedback resistor . What is the input impedance seen by the photodiode?

58 An instrumentation amplifier is composed of three op-amps. The first stage consists of two op-amps with a gain resistor and feedback resistors . The second stage is a standard differential amplifier with resistors and . If and have a high common-mode voltage , what is the common-mode voltage present at the outputs of the first stage op-amps?

59 An ideal op-amp is configured as an integrator with a resistor and capacitor . If the input is (a Dirac delta impulse) and the initial capacitor voltage is zero, what is the output for ?

60 A non-inverting amplifier is designed for a closed-loop gain of $100$. The op-amp has a DC open-loop gain of , but exhibits a dominant pole at $10$ Hz and a second non-dominant pole at $1$ MHz. What is the approximate phase margin of the closed-loop amplifier?