A CBSC second-order sigma-delta modulator in 3μm LTPS-TFT technology

Abstract

A second-order sigma-delta modulator has been implemented in 3μm low-temperature poly-silicon thin-film transistor (LTPS-TFT) technology. Since the LTPS-TFT operational amplifier has a low open-loop gain, a large offset voltage, and the poor linearity, the proposed comparator-based switched-capacitor integrator with correlated double sampling is adopted in the modulator. The whole modulator consumes 63.3mW from an 11.2V supply and occupies 26mm2 area. In a signal bandwidth of 1.56kHz for the touch panel application, the measured input dynamic range is 69dB and the measured peak signal-to-noise plus distortion ratio is 65.63dB with the duty-cycle control technique.