17.8 A 90.5%-Efficiency 28.7µVRMS-Noise Bipolar-Output High-Step-Up SC DC-DC Converter with Energy-Recycled Regulation and Post-Filtering for ±15V TFT-Based LAE Sensors

• Published in: 2021 IEEE International Solid- State Circuits Conference (ISSCC) Vol. 64; pp. 270 - 272
• Main Authors: Ko, Min-Woo, Han, Hyunki, Kim, Hyun-Sik
• Format: Conference Proceeding
• Language: English
• Published: IEEE 13.02.2021
• Subjects: Regulation; Sensors; Solid state circuits; Switches; Thin film transistors; Voltage control
• DOI: 10.1109/ISSCC42613.2021.9365935

The applications of large-area electronics (LAEs) based on thin-film transistors (TFTs) are rapidly expanding from displays to sensors. For the TFT gate drivers, high-voltage bipolar supply rails (approximately ±15V) are required; so far, they have been typically generated from a battery (V_{BAT}) by employing switched-capacitor converters (SCCs) [1]. Since a high SNR is crucial for TFT-based sensors such as an under-display fingerprint sensor [2], the noise and ripple of the SCC output, which are prone to be coupled to the readout AFE, should be minimized. As a straightforward method, an LDO can be utilized as a post-regulator in series with the SCC. However, the relatively large dropout voltage (V_{DO}) of the LDO significantly degrades the efficiency [3]. In contrast, small V DO reduces LDO loop-gain due to the pass-transistor working in the triode region, resulting in decreased supply-ripple rejection (PSR). From the perspective of SCC, owing to its fixed voltage conversion ratio (VCR), the V DO cannot be finely regulated over a wide variation of V BAT . For fine regulation, the complexity (cost) overhead or the power loss will increase in the SC circuit. In this work, an energy-recycled optimal V DO control (EROC) technique in the SC bipolar step-up stage is proposed for higher efficiency. Also, load-current-reused (LCR) post-regulator is presented to achieve high PSR while extremely minimizing the power loss at the pass-transistor.