Hello,

I'm looking for JFET,low-bias OPAMPs for EEG.

I found the AD8627 on the web site. below

http://www.analog.com/jp/content/biopotential_electrode_sensing_in_ecg_emg_and_eeg/fca.html.

So,I'd like to know the input impedance of AD8627.

The input bias current of AD8627 is pretty low.

I hope over 300G(ohm).

Best Regards,

Kou

Hi, Kou.

JFET amplifiers indeed have very high input impedance. However, we don't measure input impedance instead we measure the input bias current. Since impedance is an AC, it's not easy to measure it unlike resistance.

Relating the two parameters, if the input bias current is very low enough therefore the input impedance is a very high value. For AD8627 the input impedance is in Gigaohms to Teraohms based on the input bias current of less than 1pA. We don't have yet a numerical value of this parameter however, I had already contacted the person-in-charge of this part. I'll keep you posted on this.

Regards,

Anna