Hey guys it's me again,
I got a question conerning one of my circuits. Its a pretty simple one.
I m using a LT1227CN8 (OPAMP). I m using it as an inverting op. So there is an 1 MOhm resistance on the - input and 1 MOhm ressistance between the output (i know thats a lot). Between the positive input and ground i got a 499kOhm ressistance. On the output i got a 330pF capacitor.
So if do some math i get to a noise of (about) 80µV under the following conditions:
Temperature: 300K
Max. Frequenzy 150kHz
I also assume that the typical number given in the datasheet is constant over the the whole bandwith to 150kHz (min Frequenzy 1kHz). Which is obviously not the case since it gets lower at higher frequenzies. And higher at lower frequenzies.
My questions would be:
a) Are these assumptions viable in reality?
b) It doesnt seem to me like the cirucit has an -1 Gain (after measuring it in reality - and I dont get why)
c) The noise seems a lot higher than the calculated one. It also gets a lot higher as soon as the OPA starts working (gets his supply voltage).
Cheers, BR
Alex
/edit: the supply voltage I m using is +/- 12 generated out of the following DC/DC converter: TMR1-2422 (i used some capacitors and inductive elements to flatten the supply voltage - if that makes any sense to you)
I got a question conerning one of my circuits. Its a pretty simple one.
I m using a LT1227CN8 (OPAMP). I m using it as an inverting op. So there is an 1 MOhm resistance on the - input and 1 MOhm ressistance between the output (i know thats a lot). Between the positive input and ground i got a 499kOhm ressistance. On the output i got a 330pF capacitor.
So if do some math i get to a noise of (about) 80µV under the following conditions:
Temperature: 300K
Max. Frequenzy 150kHz
I also assume that the typical number given in the datasheet is constant over the the whole bandwith to 150kHz (min Frequenzy 1kHz). Which is obviously not the case since it gets lower at higher frequenzies. And higher at lower frequenzies.
My questions would be:
a) Are these assumptions viable in reality?
b) It doesnt seem to me like the cirucit has an -1 Gain (after measuring it in reality - and I dont get why)
c) The noise seems a lot higher than the calculated one. It also gets a lot higher as soon as the OPA starts working (gets his supply voltage).
Cheers, BR
Alex
/edit: the supply voltage I m using is +/- 12 generated out of the following DC/DC converter: TMR1-2422 (i used some capacitors and inductive elements to flatten the supply voltage - if that makes any sense to you)