Internal Input Bias Current Cancellation

模拟信号链 — Thu, 02 May 2013 02:56:46 GMT

作者： Bruce Trump，德州仪器 (TI)

在帮助选择运算放大器和仪表放大器时，我经常听到这样的声音：“我需要真正的高输入阻抗。”哦，真是如此吗？你确定吗？

Internal Input Bias Current Cancellation

The Signal — Tue, 30 Oct 2012 13:08:59 GMT

Some circuits benefit when the characteristics of two more op amps are closely matched. So inside a dual

Internal Input Bias Current Cancellation

Bruce Trump — Fri, 20 Jul 2012 17:04:28 GMT

Hi Ian. You may have a good reason to use a bias current cancellation resistor. I, of course, did not intend to rule out their use and I think you understand that. This comment area is not well suited to handle your question because you can't attach a schematic. I encourage you to post a question in the high speed amplifier forum. Though I don't normally troll the high speed amp forum, I will look for your post and comment. Be sure to include a schematic.

Internal Input Bias Current Cancellation

Ian de Vries — Fri, 20 Jul 2012 16:38:45 GMT

Hello Bruce

So I have an application that needs high bandwidth >80Mhz and slew rate >40V/us and rail to rail output swing Vs = 12V.

Input offset voltage ideally as low as possible

The amps I have found have have input offset of around 100uV, but an Input bias current of 5uA. With a gain of 5 this voltage offset will give me a output voltage offset of around 500uV.

If I use a 2k input resistor, 5uA of bias current will give me a roughly 10mV offset at the output - considerably more than the voltage offset.

Hence in this case i think it is a good idea to use the cancellation resistors ?

your comments appreciated

thanks

Ian

Internal Input Bias Current Cancellation

The Signal — Tue, 17 Jul 2012 19:24:41 GMT

In helping to select op amps and instrumentation amps I frequently hear the comment, “I need really