OP-AMP query - trouble understanding the current direction

[INS-ANI]

OP-AMP query

In basic opamp structure,i am having some trouble understanding the current direction.
I have attached an image, where both current flows from GND to the inverting and non-inverting terminal.
My question is why? for the non-inverting terminal, the current should flow towards gnd(lower potential).

 

[Kral]

Re: OP-AMP current direction

INS-ANI,
Don't be mislead by the "+" and "-" symbols. The do not represent polarity. They are simply symbols to identify the non-inverting and inverting inputs. The actual current flow direction of the bias currents can be either direction, depending on the internal circuit design of the op-amp.
Regards,
Kral

 

[INS-ANI]

OP-AMP query

@kral, thanks
I have some more questions.

1) significance of 0 dB circuit in case of an integrator.
2) How to minimise offset and drift error in an integrator.

thanks

 

[LvW]

Re: OP-AMP query

I have some more questions.
1) significance of 0 dB circuit in case of an integrator.
2) How to minimise offset and drift error in an integrator.
thanks

1.) I don´t understand the question
2.) In each case - non-inv. or inv. integrator circuit - the opamp needs resistive feedback across the capacitor.
However, in most cases the intergator is used not as a single unit but as part of a more complex circuitry (filter, control units). In all these cases there will be a stabilizing resistive "overall" feedback path and the integrator circuit itself needs no separate stabilization.

 

[Kral]

Re: OP-AMP query

INS-ANI
I also do not understand question 1.
.
I agree with LVW on question 2. The result is a 1st order lag filter, not a true integrator. This approximation to an integrator may be acceptable if the RC time constant RfCf is large compared to the interval over which the integration takes place. There are a couple more things that you can do:
.
Make sure that the resistance to ground is the same for both op-amp inputs. This will eliminaate drift due to input bias current.
.
There is nothing that you can do about drift due to input offset current, other than provide a compensating input current to the inverting input (for an inverting integrator). This can be difficult because input offset current is a function of temperature. Of course you should select an op-amp that has low input offset current.
.
Likewise, there is nothing that you can do about drift caused by input offset voltage, other than providing a compensating voltage to the NI input to the op-amp. This can also be difficult because input offset voltage is a function of temperature. Of course you should select an op-amp that has low input offset voltage.

Regards,
Kral

 

[xulfee]

OP-AMP query

0 db gain means u must set its gain 1,for reducing some practcal limitations u can use resistance equalent resistance to parallel combination of (resistances at feedback n input resistance on -ve terminal)then gnd +ve pin using this resistance

 

[LvW]

Re: OP-AMP query

0 db gain means u must set its gain 1,for reducing some practcal limitations u can use resistance equalent resistance to parallel combination of (resistances at feedback n input resistance on -ve terminal)then gnd +ve pin using this resistance

???
Do you speak still about opamp integrators ?