Re: how to raise input impedance of small signal
- From: Pooh Bear <rabbitsfriendsandrelations@xxxxxxxxxxx>
- Date: Mon, 05 Sep 2005 03:57:20 +0100
eehinjor wrote:
> Hi,everybody.
> The voltage of my signal is of mv level.this signal is the input of
> ADCs.I want to raise the input impdedance of the signal,then the signal
> will be isolated from the ADCs.
>
> Simplely,An op-amp(OPA602) is used.
>
> the signal---PIN3(IN+)
> PIN2(IN-)--PIN5(OUT)
>
> but I found the result is so bad.Such as,when the signal is about
> 2.5mV,the output of op-amp is almost 3.3mV.
>
> Who know the reason and better ways?
The OPA602 has a typical input offset voltage of 1mV
http://focus.ti.com/lit/ds/symlink/opa602.pdf
Your result is typical therefore.
You need an op-amp with better DC accuracy or you need to trim the OPA602 (
see pin 5 ).
Graham
.
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