Yuze Niu

A2.1-ppm/°C current-mode CMOS bandgap reference with piecewise curvature compensation

This paper presents a high-precision, low temperature coefficient (TC) CMOS bandgap reference for high-performance multi-channel ADC working under wide temperature range. A piecewise curvature compensation technique is proposed to extend its operating temperature range and keep its low temperature coefficient. A ß-compensation technique is used to cancel the PTAT and non-PTAT spread of the output due to variation of β in the BJTs. Moreover, the trimming resistors are implemented to calibrate the 1st-order temperature coefficient and absolute value of the output voltage. The bandgap reference designed in 0.18μm CMOS process has a super low temperature coefficient of 2.1ppm/°C over a wide temperature of −55 ° C to 140 ° C, making it appropriate to provide reference voltage for a high-precision ADC.

A low-noise closed-loop interface for high-G capacitive micro-accelerometer

A switched capacitor interface is presented in this paper for a ±50 g capacitive micro-accelerometer. In order to suppress the flicker noise of the frontend, a switched capacitor proportional-integral controller combined with a charge sensitive amplifier using correlated double sampling is proposed. The controller has a simple structure with minimized number of switches and cancels the offset of both the charge sensitive amplifier and itself. A delay buffer following the controller is used to generate a z-1/2 delay and drive the middle plate of the sensing element. The interface is implemented in a 0.35 μm 3.3 V/15 V CMOS process and the area of the chip is 11.75 mm2. The fabricated prototype circuit operates under 15 V and 3.3 V supply at a sampling clock of 100 kHz. Meanwhile, a sensitivity of 99.7 mV/g is achieved with the bias instability of 200 μg. The dynamic range of the accelerometer is 106.16 dB over a signal bandwidth of 200 Hz.

A 1.67-ppm/°C 64-ppm/V curvature-compensated bandgap reference based on a transcendental equation

This paper proposes a current-mode bandgap reference which employs a novel “coarse” voltage replication to offset the 2nd-order curvature due to base-emitter voltage of the BJT. The coarse replication is based on a process insensitive transcendental equation which regulates the independent CTAT current. The bandgap reference which will be implemented in 0.35µm CMOS process has a low operating current of 0.85µA. Under a 2.6V to 4V supply, its line sensitivity is 64ppm/V even in the worst condition, and its TC is only 1.67ppm/°C in the temperature range of −55°C to 115°C.

A digital multiplexing and real-time refresh dimming control circuit used in LED driver for multiple LED strings

This paper presents a digital dimming control circuit used in a light-emitting diode (LED) driver, allowing it to dim multiple LED strings with only two input ports which receive serial data accompanied with synchronous clock. A multiplexing technique is used to simplify the control circuit, using one DAC to transfer all the dimming messages for each string, and a real-time refresh technique is used to make the transferred dimming voltage keep a high accuracy all the time. The circuit is friendly compatible with the linear current regulator and pulsewidth modulation (PWM) dimming methods. To get a precise dimming control, we build a 10-bit segment R-2R DAC. The simulation results show the dimming voltages for each LED string keep the errors less than 0.5LSB compared with the designed voltages.