Part Number:INA129
I am using a INA129 to amplify a +/-200mV signal.
To start, I set the INA129 with these parameters: V+ = +15V, V- = -15V, REF = GND, Rg = 22.2K Ohm, Output Load = 1K Ohm (Vo to GND). Does this look right? I don't see anything wrong with this.
When I add signal to this setup, I get these results:
| Vi (mV) | Vo (mV) |
| -82.29 | -107.5 |
| -70.65 | -109.15 |
| -60.2 | -104.2 |
| -49.903 | -91.8 |
| -39.8 | -72.1 |
| -30.064 | -53.1 |
| -21.742 | -37.1 |
| -10.18 | -14.7 |
| 0.552 | 5.6 |
| 10.761 | 24.2 |
| 20.158 | 41 |
| 30.305 | 61.1 |
| 39.226 | 78 |
| 40.315 | 80.18 |
| 50.665 | 99.9 |
| 60.3 | 106.5 |
| 66.76 | 107 |
| 79.46 | 107.4 |
| 80.09 | 107.3 |
The output voltage saturates at input voltages greater than 60mV and less than -50mV. Why is the output voltage saturating? It is not even close to the power supply voltages.
Also the gain in the linear regain is not as expected, G = 1+49.5K Ohm/Rg (3.2). The actual gain is about 2. Has anyone seen something like this?
I tried different INA129 ICs, different power supplies, input sources, breadboard locations, Rg, and loads. Non of this has changed the results.