Quick questions on Summing, difference and instrumentation amplifiers - WJEC A-Level Electronics

3short 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 summing (mixer) amplifier?

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Each input feeds the virtual earth of an inverting amplifier through its own resistor. The currents add at that node and flow through the feedback resistor, so the output is the weighted, inverted sum. With equal input resistors it is simply

-\frac{R_f}{R}

times the sum of the inputs. Because the summing node is a virtual earth, the inputs do not interact, which is why this circuit mixes audio channels cleanly.

What is q1?

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A summing amplifier has two equal inputs of

1.5\,\text{V}

through

10\,\text{k}\Omega

resistors and

R_f = 10\,\text{k}\Omega

. Find the output. [2 marks]

What is q2?

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State one advantage of an instrumentation amplifier over a plain difference amplifier. [1 mark]

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