AD623-Unable to change gain or reference voltage
INA126 specs for common mode range is undefined at Vs+=3.3, Vs-=0 yet it says works to Vs=3V I can see the Vcm only shifts down with Vs+ due to high side current source voltage drop.  So I take 3.3/5 x100% of the Fig 22 mean voltage of 1.6V. this equals 3.3/5*1.6= ≈1.0V rounded down.

using 100000x more current than input bias current to minimize offset from input bias current
we get a 4 resistor solution with no loss of differential input.  from Fig 14 Ib≈14 nA so you can make 1V with &gt;1.4mA roughly even 1mA with this low impedance is OK.

thus Rpu=2.3k, Rpd=1.0k I=3.3/ 3.3k=1mA , Vth= 1/3.3 x 3.3V=1.0V. Pullup (pu) to 3.3V, Down(pd) to 0 V pref using lowest error tolerance if using gain=1000 to minimize DC out offset.
Then use a lower Zcm bias resistors for each INA input between Zsource and ZIn(INA)
my preference
Use a 1.0 V LDO with RF cap and RC bias to both inputs at 1.0V. this gives better differential noise rejection and common mode line noise rejection. Using RC=&lt;50ms and R= 50k, C=1uF
Somehow you must to define your nominal input voltage and output if you want unipolar from 0V  or bipolar centred around midscale output. TBD



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