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TLE2022AM: Input Bias current

Part Number: TLE2022AM

Hi, 

Per the datasheet of TLE2022AMD the input bias current is specified as +90nA max over temperature (page 24), but as per the graph in figure 9 the input bias current is given as negative current.

As the input stage of the TLE2022AMD consists of PNP transistors is it advisable to consider -VE current for input bias current or we should consider bias current can be either +VE or -VE.

Thanks and Regards,

Midhun

  • Hello Midhun,

    There have been different practices used for specifying the input bias current polarity sign among the various divisions, times and products. That can lead to some confusion in terms what that actual current flow direction is for an op amp and what gets stated in the Electrical Characteristics table. As you mention the TLE2022AMD lists a maximum input bias current over temperature of 90 nA. Since it doesn't have sign in front of the number one would presume the maximum input current is positive (+90 nA).

    The current convention applied to many integrated circuits is that current coming out of a pin is termed negative, and current flowing into the pin positive. The TLE2022AMD has PNP input transistors as you noted. The PNP transistor emitter arrow points into the transistor and the emitter current is equal to IE = IC + IB. The base current, which is the majority of op amp input bias current is IB and would flow out of each op amp input. Therefore, the bias current flow in reality would be negative and thus a maximum -90 nA. Since the input consists of PNP transistors and a some low leakage ESD cells the input polarity would be considered negative for the TLE2022ADM inputs.

    In many circuit applications it doesn't matter if the input bias current in reality has one polarity, or the other. However, the sign of the input bias current can affect the output referred voltage offset that includes the effect of the input bias currents flowing through their circuit paths. The bias current can result in a somewhat higher, or lower output referred voltage offset than would be had by the contribution from input voltage offset alone.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • Thanks for the confirmation Thomas.