I've attached a circuit of a circuit I am now supporting. I am pushing to have many things redesigned and one of the things I want to push is to remove U12A, the buffer.
Just to summarize, this is a diff amp with a low pass filter built in.
The reason is, that the non-idealities of the opamp will just be x2 now, and the final output just goes into an ADC so is charging up 12pF or so. The output impedance of U12B will be the same as U12A (if I change the resistor values of course). The most concerning non-ideality is the offset voltage, which can be up to +-10mV, so with two stacked up could be up to +-20mV now.
Given it is a diff amp, I realize an instrumentation grade may be better, but I am not focusing on that topic for now.
Is there something I am overlooking, or am I justified in my assertion that many Engineers tend to overdue it on the opamp unity gain buffers? I realize they have their place, but this does not appear to be one to me.
Thank you in advance.
Just to summarize, this is a diff amp with a low pass filter built in.
The reason is, that the non-idealities of the opamp will just be x2 now, and the final output just goes into an ADC so is charging up 12pF or so. The output impedance of U12B will be the same as U12A (if I change the resistor values of course). The most concerning non-ideality is the offset voltage, which can be up to +-10mV, so with two stacked up could be up to +-20mV now.
Given it is a diff amp, I realize an instrumentation grade may be better, but I am not focusing on that topic for now.
Is there something I am overlooking, or am I justified in my assertion that many Engineers tend to overdue it on the opamp unity gain buffers? I realize they have their place, but this does not appear to be one to me.
Thank you in advance.
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