Input Bias Offset Current

All op-amps have the input bias current which is the current drawn by the input terminals. It is a leakage current that sources or sinks at both input terminals. Depending on the type of input transistor, the bias current can flow in or out of the input terminals.

The op-amp datasheet usually specifies the input bias current as the average value of the input bias current IB+ at the non inverting terminal and the input bias current IB- at the inverting terminal.

The input offset current (IOS) is equal to the difference between the input bias current at the non-inverting terminal (IB+) minus the input bias current at the inverting (IB- ) terminal of the amplifier. Offset current is typically an order of magnitude less than bias current.


The magnitudes can range from nA down to pA. Generally speaking, MOSFET op-amps have smaller bias currents than BJT types.
Bipolar transistor: ~nA
The picture below shows the input bias current specification of MCP604.


Amp-titudes Episode 2 – Input Bias and Offset Current:

20th Annual
Microchip MASTERs Conference 2016
Register now - Deadline: July 29

JW Marriott Desert Ridge Resort-Phoenix, AZ

© 2016 Microchip Technology, Inc.
Information contained on this site regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip devices in life support and/or safety applications is entirely at the buyer's risk, and the buyer agrees to defend, indemnify and hold harmless Microchip from any and all damages, claims, suits, or expenses resulting from such use. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights.