Trong-Hieu Tran

A Low-ppm Digitally Controlled Crystal Oscillator Compensated by a New 0.19-mm 2 Time-Domain Temperature Sensor

A low-ppm digitally controlled crystal oscillator (DCXO) in a Pierce readout topology with a new 0.19-mm2 CMOS time-domain temperature sensor (TDTS) circuit for temperature compensation is designed and fabricated in this paper. The Pierce readout circuit is designed to output a 16-MHz oscillating signal as an important base clock for mobile devices. To cope with inevitable imprecision caused by environmental temperature variation, the readout should be compensated based on crystals frequency-temperature curve via a temperature sensor. To this end, a new low-power, small-sized, CMOS on-chip temperature sensor circuit is successfully synthesized by 20-stages of newly designed delay cells. Each delay cell is compensated by a CMOS-process-compatible varactor, enabling a TDTS consisting of only a low number of delay cells to generate long enough delay that is proportional to temperature and in required precisions. In addition to Pierce and TDTS circuits, the DCXO consists of the logics to compute capacitance correction, a switchedcapacitor array to adjust Pierce capacitances, and regulators for DCXO and TDTS. The proposed circuits are fabricated by TSMC 0.18-μm CMOS process, where the active area is 0.516 mm2 for the whole chip, while 0.19 mm2 for the TDTS. With temperature compensation enabled, the best measured frequency deviations of a calibrated TCXO is within ±0.2 ppm from -40 °C to 85 °C. The temperature resolution of the developed TDTS is successfully designed to reach 0.18 °C/LSB with an accuracy of ±1 °C validated by one of the tape-out chips.

A fast readout circuit for an organic vertical nano-junction sensor

A fast mixed-signal readout circuit for high sensitivity organic vertical nano-junctions (VNJ) ammonia sensor detection is proposed in this study. Accompanying with the ammonia sensor, a low power, fast response and high resolution readout circuit is designed and successfully taped-out in this study. The analog front-end circuit includes a pre-amplifier, a sample and hold (S/H) circuit, a differential current, a pulse width modulation (PWM) circuit, an automatically sensing and reset (S/R) circuit. The digital back-end is realized by cell-based technology to compute and display concentration values instantaneously. The chip is fabricated by the TSMC 0.18-μm 1P6M 3.3V mixed-signal CMOS process technique for verification. The chip area is 1.5 × 1.6 mm2 while power consumption is 3.2 mW. Experiment results show a strong linear relationship exists between differential S/R output slope and the gas concentration level in a logarithm scale, which is critically beneficial to sensor design. In results, the readout circuit has fast responses, 50 seconds, based on the auto-sensing circuit catching different slope coefficient of the signal in transient time. The resolution is 70.48mV/log(ppm) while error rate, average noise and detection rate reliability are 2.86%, 123 μVrms, and 99.6%, respectively. This chip could be suitable for applications in cars, cell phones, watches, etc.