The purpose of this application note is to show users of the ST7LITE2 ADC how to achieve 13-bit resolution with the internal amplifier. It also explains the software methodology, which can be applied to find and cancel the amplifier offset error. A reference application is shown with implementation of hardware and software filtering techniques (using an averaging algorithm) to minimize the ADC error.
This application note describes methods to achieve 13-bit resolution and high accuracy with the ST7LITE2 ADC, which features a 10-bit successive approximation converter with an internal amplifier. The document details the software methodology to find and cancel the amplifier offset error and demonstrates the implementation of hardware and software filtering techniques to minimize ADC error.
| Resolution | 10-bit successive approximation converter |
|---|---|
| Analog Input Channels | 7 multiplexed analog input channels |
| Amplifier Gain | 8 |
| Max Input Voltage (Amplifier ON, 5V Vpp) | 500mV |
| Max Input Voltage (Amplifier ON, 3.6V Vpp) | 350mV |
| Total Unadjusted Error (TUE) | +10LSB |
13-bit resolution is achieved by using the internal amplifier to amplify small signals, allowing the minimum measurable signal to be 0.6103mV at 5V.
The offset is introduced to keep the driver transistor in the active region and avoid nonlinearity in the transfer curve around 0V input.
The offset is compensated by recording the output corresponding to 0V input (using AMPCAL=1) and subtracting it from all amplified-and-converted digital codes.
The measured gain error, including ADC inaccuracies, is around 6% at 25 °C.