Sponsored by Texas Instruments
Precision Successive-Approximation-Register (SAR) Analog-to-Digital-Converters (ADC) are the preferred converters for fast reacting systems requiring zero or close to zero conversion cycle latency. However, the wide bandwidth that gives these converters their amazing low latency also allows them to see more noise. Thus, to prevent noise performance degradation, we will be discussing the top five common design oversights: lack of anti-aliasing filter, wrong placement of anti-aliasing filter, relatively high impedance source, narrow bandwidth drivers, and slightly unstable drivers.
Also, to help troubleshooting these design oversights, we present and analyze noise performance of circuits having ADS7945/6 (2MSPS 14 bits) and ADS8318/9 (500KSPS 16 bits) SAR ADCs. The analysis incorporates frequency domain noise of DC signals, where the shape of noise floor is used to differentiate between the typical white noise and noise associated with driver oscillations (instability).