Self calibration circuitry and algorithm for multipass analog to digital converter interstage gain correction

摘要

Autocalibration circuitry and an algorithm (method) for aligning interstage gain within a high resolution multipass analog-to-digital converter. The interstage gain alignment technique maximizes the signal-to-noise ratio and spurious free dynamic range of the multipass analog-to-digital converter. The multipass analog-to-digital converter uses an m-bit course analog-to-digital converter and an n-bit fine analog-to-digital converter whose input is derived from an m-bit digital-to-analog converter. Output words of the course and fine analog-to-digital converters are combined to produce an output word of the multipass analog-to-digital converter. The present invention applies a random signal into the m-bit digital-to-analog converter. The digital output of the n-bit fine analog-to-digital converter is statistically examined to discern the gain misalignment error. The sign of the gain misalignment error is correlated with the sign of the random signal applied to the m-bit digital-to-analog converter to null the gain error independently of the input signal sampled by the multipass analog-to-digital converter and without interrupting the conversion process of the multipass analog-to-digital converter. The present invention thus utilizes statistical averaging of the product of the error term that is minimized and a pseudo random signal in the digital domain without interrupting the analog-to-digital conversion process. This provides for continuous optimization of the interstage gain, thereby compensating for errors related to temperature, aging and other environmental factors that cannot be achieved using traditional laser trim techniques, for example.