[SI-LIST] Re: operational amplifiers

  • From: "Juergen Flamm" <jflamm@xxxxxxxxxxx>
  • To: <mike_bihan@xxxxxxxxxxxx>, "List` Si" <si-list@xxxxxxxxxxxxx>
  • Date: Thu, 9 Oct 2003 08:10:15 -0700

Also, depending upon the input parasitics (e.g. capacitance), the =
bandwidth of the amplifier and the circuit topology used, large value =
resistor (like 50K) in the feedback can easily turn the amplifier into =
an oscillator. Performing a stability analysis taking parasitics into =
consideration should mitigate this behavior. =20

Juergen Flamm


-----Original Message-----
From: Bi Han [mailto:mike_bihan@xxxxxxxxxxxx]=20
Sent: Wednesday, October 08, 2003 9:14 PM
To: List` Si
Subject: [SI-LIST] Re: operational amplifiers

also depends on that you have feedback in your op-amp or not.
steve weir <weirsp@xxxxxxxxxx> wrote:Zhangkun, if you mismatch the =
driving impedance then you will see a=20
corresponding shift in offset voltage due to the bias current of the=20
Op-Amp. For CMOS inputs, the current is very low, and a difference of =
45K=20
may mean a lot less error than say contamination on the PCB. But, if you =

are using a bipolar device, 45K may translate to a number of mV=20
offset. You just have to plug those numbers into your error budget and =
see=20
where you end up.

Regards,


Steve.
At 10:40 AM 10/8/2003 +0800, Zhangkun wrote:
>Dear All:
>We are doing some simulation about operational amplifiers. I have one=20
>question about the input of operational amplifiers. If the input =
impedance=20
>of inverting input and non-inverting input are not same, does the=20
>operational amplifiers work normally?
>
>For example, the resistor between vin- and inverting input of =
operational=20
>amplifiers is 5K ohm and the resistor between vin+ and non-inverting =
input=20
>of operational amplifiers is 50K ohm. Will the operational amplifier =
work=20
>normally?
>
>Best Regards
>
>Zhangkun
>2003.10.08
>
>
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