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The current noise density of LMP7721

yi-an huang
Prodigy 10 points
Other Parts Discussed in Thread: LMP7721

I am trying to use the LMP7721 in very low current (100fA-10pA) measurement, to my surprise, the amplifier has very big current noise density 0.01pA/√Hz, 100times than LMC6001,INA116 and others, even more than AD8628, which bias current is 30pA.

              

             Bias current (Typ)       Current noise density

PLM7221        3fA                   10fA/√Hz  (1kHz)

LMC6001A1     10fA                  0.13fA/√Hz  (1kHz)

INA116PA          3fA                   0.1fA/√Hz  (1kHz)

AD8628          30pA                  5 fA /√Hz  (10Hz)

I wonder that it is a mistake in the LMP7721’s data sheet or the amplifier can’t be used in low current measurement for it has so big current noise density. I really want to know the performance of the LMP7721's current noise ( I p-p 0.1-10Hz). If the Current noise density is 10fA/√Hz  (1kHz), the current noise ( I p-p 0.1-10Hz) may be 60-100fA or more, in this case, how to measure the bias current 3fA (typ)?

 

Thanks

 

Huang yi an  

Shanghai Taiou Electronic Co., Ltd   Shanghai China

E-mail yah1951@163.com

2012-1-12

  • 0
    TI__Genius 12345 points

    Yi-an,

    The current noise spec of the LMP7721 is correct in the datasheet, as discussed in this thread:

    http://e2e.ti.com/support/amplifiers/precision_amplifiers/f/14/t/157294.aspx#576453

    I will try to track down further information on the current noise spectral density for the part.