This is the reference circuit about the AD8253 and AD7985.
There are differencial input ports in the AD8253 and I want to use this device for single input.
Then how can I connet the other input pin?
I'll let the InAmp guys answer your 8253 question, but watch out with the 10k/10k divider for
the 4.5V. If you have any noise, even 1 or 2 mV of noise or switching regulator trash on your
4.5V rail, it will be divided by one half and show up on the 2.25V line. This will go directly into
your signal path in two places. Because the input impedance of the 4004-2 is high, you can
increase the resistor values, say to 100k, and then put a big cap, maybe 1 uF, on the junction
that goes to the non-inverting input of the op amp.
The ADR43x family is my favorite reference family because you can put a series R-C on the
comp pin and get rid of noise peaking. See "High Frequency Noise" on pages 16-17 of the
ADR439 datasheet. I would also add at least a 0.01uF cap on the input and output pins of
When you are using a 16 bit ADC at high conversion rates, microvolts of noise can sneak in
anywhere, so pc board layout and stackup dimensions are also critical.
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