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I want to use a PGA (programmable gain amplifier). I found the LMH6881 which I will be probably using.

On page 5 of the datasheet you can see that the analog input voltage range should be between 0V and VCC (which is 5V). On page 6 of the datasheet it is stated that the input common mode voltage is 2.5V (self-biased).

So why isn't it possible to apply a single-ended -2.5V signal to the analog input. If it is self-biased then it should still be in the range of 0V to 5V, right?

ErikR
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Yoomo
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    no, it shouldn't. Why do you think it should? – Marcus Müller May 24 '21 at 10:25
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    a -2.5 V signal is not in the range 0 to 5 V. This is not an opamp, it has an input impedance of 50 ohms, not the 100s of megohms you'd expect from an opamp. – Neil_UK May 24 '21 at 10:25
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    and a PGA is not an opamp, so I'm fixing both your title and your tags. – Marcus Müller May 24 '21 at 10:25
  • @MarcusMüller because of the 2.5V self biased input. I thought it raises the voltage level of the incoming signals by 2.5V – Yoomo May 24 '21 at 10:30
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    no, it's a self-biased input; that means that AC-coupled signals are biased towards that, not that things are shifted. I mean, if all signals would be shifted to the same voltage, what would the thing then amplify? – Marcus Müller May 24 '21 at 10:38
  • @MarcusMüller ok thank you I got a little bit confused. – Yoomo May 24 '21 at 10:45
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    A self biassed input to mid rail (2.5 V) is likely to be two equal resistors connected to GND and VCC, with the mid point connected to the input. The signal is then expected to be connected to this through a capacitor. – Neil_UK May 24 '21 at 11:25

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