A VCO-Based Readout ADC for Quasi-Static Sensing Applications in 3-µm Low-Temperature Poly-Silicon Thin-Film Transistor Technology

This paper presents a voltage-controlled oscillator (VCO)-based readout ADC for quasi-static sensor applications. The proposed VCO-based ADC is implemented in a low-temperature polycrystalline silicon thin-film transistor (LTPS-TFT) process. To mitigate the severe offset and flicker noise in the TFT technology, this design adopts a relaxation-based VCO and a system-level chopping scheme. To improve the linearity and widen the input range, a foreground 3rd-order polynomial-fitted compensation is adopted in this design. This readout ADC is fabricated in a 3-µm LTPS-TFT process and occupies a core area of only 3.6 mm
²
. With a 5-V supply voltage, the proposed VCO-ADC achieves a 48.2-dB SNR with a 0.6-V input at a bandwidth of 250 Hz. The total power consumption is 505 µW. The ADC’s dynamic range is 59.5 dB. The corresponding Walden’s figure of merit (FoMw) is 4.8 nJ/conversion-step.