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2 marksOperational Amplifiers

CAPE Physics Unit 2 · May/June 2023 · Paper 2 · Question 2(a)(iii)

An operational amplifier (op-amp) can function as a comparator. Figure 3 shows an op-amp comparator circuit.

The amplifier in Figure 3 on page 10, has a gain, A = 10^6, and is powered by a supply voltage, V_s, of ± 5 V. Determine the differential input voltage, ΔV, that will result in saturation with a negative voltage on the output. Assume there is zero input offset voltage.

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Other parts of this question

  1. 2(a)(i)Write an equation to show the relationship between the output voltage, V_out, and the inputs, V1 and V2.[1 mark]
  2. 2(a)(ii)Using the equation in (a) (i), briefly explain how a comparator works.[3 marks]
  3. 2(b)Explain how the circuit in Figure 4 will function to trigger the alarm if the temperature drops below the threshold value.[8 marks]
  4. 2(c)Determine the overall voltage gain of the circuit.[8 marks]
  5. 2(d)State what is meant by the 'bandwidth of an operational amplifier'.[1 mark]
  6. 2(e)(i)On Figure 6, insert EACH of the following labels: f_c and f_u. State the numerical value of the frequency at EACH point on the graph. Cut-off frequency, f_c…[4 marks]
  7. 2(e)(ii)Determine the gain of the amplifier at 1 kHz.[3 marks]

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