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I am new here, so if I am posting in the wrong area, please let me know.

Recently at the university I've had a guest lecturer, that works at Cochlear developing medical implant for the hearing impaired. This guest lecturer mentioned and drew an example diagram of a buffer amplifier with a 10V rail to ground supply with an input voltage between 1-10V, which would mean an ideal output of 1-10V since its a buffer. He also mentioned about additional voltages added with Vin such that if Vin = 1V(min), an additional 0.5V would be added to it hence Vin = 1.5v... or Vin of 10V(max) = 10V + 0.5V = 10.5V ranging between 1.5V-10.5V!? Unfortunately I was unable to ask after the lecture and he was very brief with it. But this has been bugging me, since I don't have any idea, why this would be useful, to have additional voltage at the input in that kind of implementation?

peterh
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flabbergastt
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  • If Vin becomes 1.5 volts after adding 0.5 volts then Vout becomes 1.5 volts because it (presumably) is a unity gain buffer. You can't go higher than 10 volts in and expect a output to somehow rise above 10 volts. – Andy aka Sep 16 '14 at 10:47
  • Hey, thanks for the reply. That's exactly my thought but why would it be practical to add 0.5v in the first place? assuming that is still within range and doesnt exceed 10v – flabbergastt Sep 16 '14 at 11:04
  • I think you need to do a bit of research on buffer amps. As to the practicalities of adding 0.5 volts - this can be achieved very easily with some circuits. – Andy aka Sep 16 '14 at 11:38
  • Yeah, I've done some spice simulations. I used a difference amplifier and set the gain to 1 (Rf=Ri) and made V+ = -0.5v and V- = Vin consequently giving Vo = (Vin-V+)x(Rf/Ri) to achieve a Vin+0.5v = Vout. I'm just confused with the idea of needing the additional 0.5v but i'll do more research on that. – flabbergastt Sep 16 '14 at 11:48
  • I want to share my suggestion,but I'm not sure.If any wrong in my statement please intimate me.I think the resultant voltage of 0.5V added with input voltage at output side. I mean if Vin=1V then output voltage will be 1.5V.Because it is buffer amplifier right?. Because of signal amplification (@ hearing aid) purpose that voltage amplification done. – victory Sep 16 '14 at 11:34
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    Perhaps the amplifier wasn't a rail-rail type and simply needed to be lifted away from the ground rail to prevent distortion. – JIm Dearden Sep 16 '14 at 12:39

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