single supply 2 op-amp instrument amplifier with bi-polar input

[Mr.Cool]

single supply 2 op-amp instrument amplifier with bi-polar input, is this possible? i keep reading that it is, then i simulate it and doesn't work. my input is +/- 50V, so that might be part of the issue.

 

[esp1]

hi,
Check your Vref polarity.
E
LTSpice sim image.

 

[FvM]

You know that OPs have input voltage range specification.

The presented circuit can work
- using appropriate voltage dividers as suggested by the sketched schematic
- connect the divider foot point to mid supply rather than ground

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LTSpice sim image

The OP must offer a common mode range down to 0.5 V below negative rail. Not a common feature at least. I suspect an over-simplified simulation model.

 

[Mr.Cool]

esp1, its a 2 op-amp IA so its a bit different.

FvM - putting the reference on the divider worked, thanks! the resulting circuit has somehow a 50mV offset on the output, not sure where this is coming from.
I suppose I could use a 2.5V REF chip from analog devices for this?

feels super akward to offset the filter cap like this though.. i dunno, my gut feeling is to just use +/-5V supply to the opamps instead

do you think a divide by 500 (followed by a multiply by 10) as a first stage will be good if the input is only 2volts? to small a signal?

 

[FvM]

the resulting circuit has somehow a 50mV offset on the output, not sure where this is coming from.

Not by design. Need to notice that unbalanced source resistance can generate an offset.

To achieve good common mode rejection, the voltage dividers must be well matched, e.g. 0.1 % for 60 dB CMRR. Differential amplifiers with built-in precision resistor networks like INA117 are hart to beat in this regard.

To decide about supply voltage range and OP selection, all application specifications must be considered.

I would always tie the filter capacitors to signal ground, and filter the reference against ground, too.

 

[Mr.Cool]

ha, ya you're right. ok, revised. still, not convinced this will work.. also there's a reason i can not use the op-amp you selected, i need a single line out to the +/-50V. is strange, i know.

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anywho.. charge pump it is

 

[FvM]

not convinced this will work

The circuit looks O.K. now, check it.