Two OPA Instrumentation Amplifier With M0 Devices
1 Description
This subsystem software example creates a two OPA instrumentation amplifier (INA) using an MSPM0 and external resistors. In this configuration, the difference between Vi1 and Vi2 is amplified, and outputs a single-ended signal with high common-mode rejection. The output of the integrated INA can be sampled using an internal ADC channel of the device.
Figure 1-1 Subsystem Functional Block Diagram2 Required Peripherals
This application requires the two OPAs integrated in the MSPM0, and an ADC for sampling the results
| Subblock Functionality | Peripheral Use | Notes |
|---|---|---|
| OPA | OPA0 | Pins are configured in SysConfig based on what input sources are selected |
| OPA | OPA1 | |
| ADC | ADC0 | Used to measure the output voltage of the INA |
3 Design Notes
The design of the two op amp instrumentation amplifier using the integrated amplifiers of the MSPM0 is not different from the design using discrete op amps. The Two op amp instrumentation amplifier circuit application note covers the design notes for this circuit. These are paraphrased in the following list for convenience:
- Rg sets the gain of the circuit.
- High-value resistors can degrade the phase margin of the circuit and introduce additional noise in the circuit.
- The ratio of R4 and R3 set the minimum gain when Rg is removed.
- Ratios of R2 / R1 and R4 / R3 must be matched to avoid degrading the DC CMRR of the instrumentation amplifier and to make sure the Vref gain is 1V/V.
- Linear operation is contingent upon the input common-mode and output swing ranges of the discrete op amps used. The linear output swing ranges are specific under the AOL test conditions in the device data sheet.