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AS 1 Electronic and Microelectronic Systems

Quick questions on Operational amplifiers and comparators: voltage comparison and gain - CCEA A-Level Technology and Design

4short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is the op-amp as an amplifier?
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Inverting amplifier (input via RinR_{in} to the - input, feedback RfR_f): $Gain=−RfRin,Vout=−RfRin Vin.\text{Gain} = -\frac{R_f}{R_{in}}, \qquad V_{out} = -\frac{R_f}{R_{in}}\,V_{in}.Non−invertingamplifier(inputtothe+input): Non-inverting amplifier (input to the + input): Gain=1+RfRin.\text{Gain} = 1 + \frac{R_f}{R_{in}}.$ The inverting gain is negative (output inverted); the non-inverting gain is always greater than one and keeps the same polarity.
What is q1?
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As a comparator, when does the op-amp output go high? [1 mark]
What is q2?
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An inverting amplifier has Rf = 47 kilohm and Rin = 4.7 kilohm. State its voltage gain. [2 marks]
What is q3?
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What is the purpose of the reference voltage in a comparator sensing circuit? [2 marks]

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