Hi AAC. About that time again for me to bother you with what is no doubt an easy question, it's got me stumped.
If you see the attached diagram, the question is what is the gain of the circuit when the switch is open and closed. Open is easy, as the non-inv input forms a virtual earth and the gain is just -Rf/Ri: lovely jubbly.
However when the switch is closed, I enter a world of pain.
Obviously some of the initial current, well the larger portion of it, will flow down to the 27k resistor, but I have no idea how this relates to gain, so far I have only dealt with voltage differences being amplified.
To me, the non-inverting input will be at Vi as there are no resistive elements between the input and the terminal, but there is surely no way that the inverting input could be at Vi owing to the 56k resistor.
I have the answer sheet giving +1 gain, but would appreciate some advice.
Many thanks,
Fraser
If you see the attached diagram, the question is what is the gain of the circuit when the switch is open and closed. Open is easy, as the non-inv input forms a virtual earth and the gain is just -Rf/Ri: lovely jubbly.
However when the switch is closed, I enter a world of pain.
Obviously some of the initial current, well the larger portion of it, will flow down to the 27k resistor, but I have no idea how this relates to gain, so far I have only dealt with voltage differences being amplified.
To me, the non-inverting input will be at Vi as there are no resistive elements between the input and the terminal, but there is surely no way that the inverting input could be at Vi owing to the 56k resistor.
I have the answer sheet giving +1 gain, but would appreciate some advice.
Many thanks,
Fraser
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