Modeling and post-correction of pipeline analog-digital converters

Sammanfattning: Integral nonlinearity (INL) for pipelined analog-digital converters (ADCs) operating at radio frequency is measured and characterized. A parametric model for the INL of pipelined ADCs is proposed and the corresponding least-squares problem is formulated and solved. The estimated model parameters are used to design a post-correction block in order to compensate the pipeline ADC. The INL is modeled both with respect to the ADC output code k and the frequency stimuli, which is dynamic modeling. The INL model contains a static and a dynamic part. The former comprises two one-dimensional terms in ADC code that are a sequence of zero-centered linear segments and a polynomial term. The two-dimensional dynamic part consists of a set of polynomials whose parameters are dependent on the ADC input stimuli. The INL modeling methodology is applied to simulated and experimental data from a 12-bit commercial ADC running at 210 MSPS. It is demonstrated that the developed methodology is an efficient way to capture the INL of pipelined ADCs running at radio frequency. The concept of ADC digital output post-correction by INL is firstly introduced. Further, the estimated INL model is used for ADCs post-correction. The INL model is subtracted out of the digital output for post-correction. The static compensation part is made by a set of gains and offsets, that each (gain and offset) corrects an output code k range. The dynamic information, i.e. frequency dependency of the INL dynamic component is used to construct a set of filters blocks that perform ADC compensation in the time domain. The compensation scheme is applied on measured data of two ADCs of the same type (Analog Devices AD9430). Performance improvement in terms of spurious free dynamic range, signal to noise and distortion ratio, intermodulation distortion and noise are obtained. The frequency-dependent dynamic compensation can be generalized by making the use of the likely similar frequency information of the INL models (of different ADCs of the same type) to achieve a cross-ADC compensation, i.e. post-correcting of one ADC by the INL model of another converter.