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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Re: Contd posted by Jon Risch on December 7, 2002 at 08:23:52:
Having checked the math with the relevant parameters, I must respectfully conclude that you are labouring under a serious misunderstanding.At 100 ohm source impedance, the voltage noise of the op-amp dominates the noise figure. The correct choice of op-amp is thus one with a low voltage noise. A high current noise will not be important. The AD797 or similar is eminently suitable.
Whether the circuit is conceptually a voltage amplifier or a transimpedance amplifier is not relevant to the output noise.
High impedance current sources are indeed as you say, however: photodiodes and pyroelectrics, for example, must be used with op-amps with extremely low input currents, cf OPA128, but that is because their impedance measures in the 100's of megaohms.
- rjm
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Follow Ups
- Re: Contd - RJM 12/9/0207:21:01 12/9/02 (1)
- I actually went with LT1028 over AD797 in strain gage amplifiers - jcox 08:54:16 12/9/02 (0)
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