An Analog Front-End Transimpedance Amplifier with DC Photocurrent Cancellation for Gas Sensing Applications
| Autor: | Deng-Kai Lin, 林登凱 |
|---|---|
| Rok vydání: | 2018 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 106 This thesis presents the design of analog front-end (AFE) circuits for gas sensing applications. In a gas sensing microsystem, the AFE circuit is the most critical building block, since it must amplify weak signal in the presence of large interferences. A PCB prototype circuit and an on-chip front-end TIA circuit are implemented and verified. The first work is a two-stage transimpedance amplifier with auto-calibration. The noise of circuit is minimized by using batteries as voltage source and limiting circuit bandwidth to 1 Hz. The auto-calibration of the TIA is realized by digital control from the microcontroller. A portable CO2 detection device is constructed with the TIA integrated-in, and the slopes of voltage change under different concentrations of CO2 are calculated to extract the gas concentration. It demonstrates a minimum detection concentration of 4%. The second work presents an analog front-end transimpedance amplifier with DC photocurrent cancellation. Chopping technique is utilized in this work to reduce the effect of amplifier offset and flicker noise. A digital calibration loop is implemented to cancel the large DC photocurrent and increase the detection dynamic range. The chip is fabricated with UMC 0.18-μm CMOS process. The core area is 0.28 mm2 and it consumes 0.67 mW from 1.8-V supply when the current DAC is disabled. It achieves a SNR of 62.4 dB under 1-kHz bandwidth with the current DAC disabled. The results prove the feasibility to integrate this circuit in a CO2 detection system, achieving detection resolution of 50 ppm. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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