To reduce the complexity of the front-end electronics of systems with large number of channels, we have proposed a novel analog-to-digital conversion method based on non-uniform 2-bit sigma-delta modulation. The proposed method simplifies the data acquisition for gamma-ray detectors that require waveform capture to perform analyses such as pile-up detection, pulse-shape discrimination, and maximum-likelihood energy and timing estimation. The modulator consists of an integrator, three comparators with programmable thresholds, one R-2R ladder digital-to-analog converter, and a field-programmable gate array. We have designed a nine-channel front-end board based on a combination of 1-bit SDM for energy estimation, and 2-bit SDM for timing estimation and waveform analysis. In this work, we present the characterization of the non-uniform 2-bit sigma-delta modulator for gamma-ray detection. The metrics utilized to measure performance are integral non-linearity, differential non-linearity, and timing resolution.