| ??? 04/10/07 02:57 Read: times |
#136887 - Offset nulling in low cost OpAmps.. Responding to: ???'s previous message |
Suresh said:
For compensating Input Bias Current:
Adding compensation Resistor (Rcomp) at the non-inverting terminal. For compensating Total output Offset Voltage: A trim pot with end pins connected to a bipolar supply and the wiper connected to input resistor of inverting input. So that the Opamp is set to zero output initially using this pot. Would this be a better solution 'or' is there a better way to do this? Kai Klaas said:
This is dangerous, because you will couple all the noise and voltage fluctuations of the supply voltages into the inputs. And without adding proper low pass filtering this can also result in instability. In former days this was the only way to furtherly improve the performance of chip by adjusting the offsets (which were very low for that chip at that time, by the way). Today you will simply take a better OPamp. Kai Hello Kai and other members, I attended an interview yesterday were i experienced a question on offset nulling. I explained the technique that i have described above for nulling the offset voltages. But, the interviewer said, that was not the actual way to do and asked for a beter solution. I also discussed with him on choosing a better Opamp but he disagrees by saying that would cost more and asked how to do offset nulling by choosing an Opamp that is cheaper. I said iam not aware of any better technique other than what i have said. So what i want to know is, is there any better technique for providing offset nulling in low cost Opamps say for instance LM 358? regard's Suresh. |
