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DDC112 Input bias direction

Keiichi Kajino
Expert 2365 points
Other Parts Discussed in Thread: DDC112

I am assuming that polarity of input bias current is

1) Inbound (flow in into device) is plus

2) Outbound (flow out from device) is minus

Am I correct? Is the input bias current of DDC112 is typically flow into device?

Also I guess this current does not effect measurement result because this will dissapear(i.e. leak current) without goes into integ. circuit.

Am I also correct?

 

  • 0
    TI__Mastermind 18285 points

    Keiichi,

    I'm assigning your post to the correct applications engineer. He should respond soon.

  • 0
    TI__Guru 65610 points

    Keiichi-San,

    Yes typically we define the current direction this way but anyone can define the current direction a different way. We specify the current as +/-0.5pA typical because it can be either direction, into or out of the device depending on device mode, PCB leakage paths, device-to-device variation. Ideally this current is so small that it will disappear when actual device current is present from a photodiode or similar.

    Regards,

    -Adam

  • 0 in reply to Adam Sidelsky
    Expert 2365 points
    Adam,

    Thank you for youre reply. I understood the values mean.

    BTW, I got question from our customer as follows,
    ... If the current derection is minus(means flow out from device), the 10pA(max) of input bias current exceeds negative full-scale input
    when Integ. time eq to 1s @range 1(Typ 50pC)

    Is this assumption correct? I guess this current is NOT always originate from integ. cap, but I am wondering how should I answer rationally.