04/27/17 The ADA4530-1 has a FET input, does it not?

The ADA4530-1 has a FET input, does it not?  Could you talk about FET input vs. switched capacitor opamp inputs with respect to offset drift and VOS change at temperature?”

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  • On behalf of Vicky Wong.

    The ADA4530-1 indeed has a FET input. It’s offset voltage is specified at 40uV at 25C and 150uV over entire temp range. Offset drift is 0.5uV/C max for operating temp between 0 and 125C and 2.8uV/C for operating temp between -40C to 0C.

    When you mentioned switched cap input op amps, I am assuming you are referring to zero-drift amplifiers, where the inputs are constantly self correcting for dc errors over time and temp. To put things in perspective, our newest zero-drift amplifier, ADA4522 has offset of 5uV at 25C and 7+uV over full temp range. Offset drift is 20+nV/C max.

     

    In terms of offset and drift with respect to temperature, zero-drift amplifiers have better specifications, hands down. Often times however, these zero-drift amps have considerably larger input bias current (hundreds of pA or nA range over temp). In low level current or high source impedance applications, FET amps are hence often used.

    ADA4530-1 is ideal for ultralow level current systems with its fA input bias current. It’s offset and drift spec are actually pretty good as well.

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