three noise maker, but different output offset

[canlu]

hi.
i have this circuit with op37 op-amp, and repeated three time.

but at output i have different offset according to pictures:

every thig is same and resistor's are 1%.
even in the output i have mkt cap.
what can cause such behavier in this circuit?

 

[KlausST]

So Vout = 1001 x 20 mV ~= 20V which would sat the OpAmp output.

wrong

Klaus

 

[danadakk]

Yes for sure, did not factor in Aol and Ioff, here is update (using parameterized OpAmp) :

Done of first stage last schematic.


Regards, Dana.

 

[KlausST]

Hi,

to help the OP, what do you suggest him to do?

Klaus

 

[danadakk]

Post # 20.

 

[canlu]

i'v been decreased R4 to 30K, so gain reduced to 30 and now feedback current is enough.
but i have output offset -2.6 ~ 6V.
And of course, when the input has an offset, the output will also have an offset too.
input and output signal of first stage:

now what?
thank's in advance

 

[danadakk]

Are you replicating the entire circuit 3 times or just the output amps 3 times ?

 

[canlu]

Are you replicating the entire circuit 3 times or just the output amps 3 times ?

entire circuit 3 time...

 

[danadakk]

I am thinking noise differences due to zener knee device to device
differences there is no "matching". Nothing in datasheet that gives
pk-pk min/max or its distribution. Its a statistical process, not deterministic.

As far as any other differences the 1 uF coupling cap tolerance and leakage
one part to another is poor. The tolerance is+/- 20%, so V divider effect
with 1 Mohm R will effect both offset and G in signal path. leakage can be
in uA range = volt(s) of offset due to 1Mohm, and bias current of OpAmp.


Regards, Dana.

 

[canlu]

maybe, i have different voltage across zener's (9.2 ~ 9.7)
but circuit have 1% resistor's.
however i expected after capacitor i have centered GND and but not with an offset.
i'll try decrease zener resistor (R1).

 

[danadakk]

You might take this into consideration (eg. current impact on output) :

Leakage current capacitors :

DCL Leakage Current Characteristics of Capacitors

Basic Concepts Capacitors

passive-components.eu

Regards, Dana.

 

[canlu]

1more question:
i have op37 with +-15V supply
so output swing would be +-14V or a bit more...
but according to output i have +19 and -10V
what's happend here?

 

[KlausST]

but according to output i have +19 and -10V

which OPAMP´s output?
--> have a look at it´s input, and it´s output load.

How do you come to +/-14V information?
Even datasheet values are max 13.8V .. but go down to +/-10V on 600 Ohms load

Klaus

 

[danadakk]

1more question:
i have op37 with +-15V supply
so output swing would be +-14V or a bit more...
but according to output i have +19 and -10V
what's happend here?

I must not be following what you are doing, how do you get +19 out of
an OpAmp powered with +/- 15 ?


Regards, Dana.