Adaptive digital correction of analog errors in MASH ADC's - Part I: Off-line and blind on-line calibration

Cascaded delta-sigma (MASH) modulators for higher order oversampled analog- to-digital conversion rely on precise matching of contributions from differ ent quantizers to cancel lower order quantization noise from intermediate d elta-sigma stages. This first part of the paper studies the effect of analo g imperfections in the implementation, such as finite gain of the amplifier s and capacitor ratio mismatch, and presents algorithms and architectures f or digital correction of such analog imperfections, as well as gain and spe ctral distortion in the signal transfer function. Digital correction is imp lemented by linear finite-impulse response (FIR) filters, of which the coef ficients are determined through adaptive off-line or on-line calibration. O f particular interest is an on-line "blind" calibration technique, that use s no reference and operates directly on the digital output during conversio n, with the only requirement on the unknown input signal that its spectrum be bandlimited, Behavioral simulations on dual-quantization oversampled con verters demonstrate near-perfect adaptive correction and significant improv ements in signal-to-quantization-noise performance over the uncalibrated ca se, using as few as 5 FIR coefficients. An alternative on-line adaptation t echnique using test signal injection and experimental results from silicon are presented in the second part, in a companion paper [1].