• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 49 subscribers
  • Views 756 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

INA827: Minimum Input Bias Current

Joshua Rowe
Prodigy 20 points
Part Number: INA827

Hi,


We are using the INA827 instrumentation amplifier as the first stage in an IF circuit to convert a differential signal to a single ended signal. For biasing we have a resistor connected between each of the input lines and a Vcc/2 source. For filter reasons we would like to make these resistors as high as possible in order to reduce our high pass cutoff frequency.

However, when we increased the resistors to 1M each the output flatlined. I noticed that there is no minimum input bias current listed on the data sheet, only a typical and maximum. Do you have any information on what the minimum input bias current is or if not what the minimum common mode DC voltage is so we can choose resistors of the highest value possible while still preserving the integrity of the output?

For your reference this is the circuit configuration. The resistors R61 and R62 are what we are trying to maximize.

Thanks,

Josh

  • 0
    Guru 140200 points

    Hi Joshua,

    you must consider a maximum input bias current of 95nA. This current will flow across R61 and R62 and will shift the common mode input voltage of INA827. The following picture shows that with your settings a common mode input voltage of up to 2.2V should be possible:

    (2.2V - 1.65V) / 95nA = 5.8M. So, 1M resistors for R62 and R63 should not be a problem.

    But don't forget the input offset current of INA827: 10nA x 1M = 10mV. This is one third of your input voltage range!

    Kai