Adaptive Digital Correction of Analog Errors in MASH ADC’s—Part II: Correction Using Test-Signal Injection

The first part of this two-part paper, published separately, discusses the quantization noise leakage problem caused in cascaded delta–sigma (MASH) analog-to-digital converters (ADC’s) by the imperfections of the first-stage analog circuitry. It also proposes adaptive digital techniques based on detecting and minimizing the leakage noise in the output signal. In some cases, this is difficult to accomplish, since the noise is correlated with the input signal, and since the adaptation relies on acquiring the unknown out-of-band noise signal. The second part of the paper, given below, describes a different adaptation strategy. It relies on the injection of a pseudorandom two-level test signal at the input of the first-stage quantizer, where it is added to the quantization noise. The test signal then leaks into the output signal, where it can be detected and used to control the digital noise-cancellation filter. This paper describes the correction process, as well as some efficient structures for implementing it, and demonstrates the effectiveness of the technique by describing three design examples.