A SecondOrder HighResolution Incremental A/D Converter with Offset and Charge Injection Compensation

Sigma-delta modulation, associated with oversampling and noise shaping, is a well-known technique used in high-accuracy A/D converters. Such converters, required in telecommunications applications, are characterized by ac perfonnance such as signal-to-noise ratio. Moreover, they are mainly dedicated to applications which can tolerate offset and gain errors. On the other hand, measurement and instrumentation applications require absolute accuracy, e.g., offset and gain errors cannot be tolerated. These applications are characterized by dc perfonnance such as differential and integral nonlinearides, offset and gain errors, and they often require high resolution. The second-order incremental A/D converter, which makes use of sigma-delta modulation associated with a simple digital filter, is capable of achieving such requirements. Experimental results, obtained of circuits fabricated in a SACMOS 3-¿m technology, indicate that 15-bit absolute accuracy is easily achievable, even with a low reference voltage.