A low power and high performance with third order delta-sigma modulator for audio applications, fabricated in a 0.18 µm CMOS process, is presented. The modulator utilizes a third order noise shaping with only one opamp by using an opamp sharing technique. The opamp sharing among three integrator stages is achieved through the optimal operation timing, which makes use of the load capacitance differences between the three integrator stages. The designed modulator achieves 101.1 dB signal-to-noise ratio (A-weighted) and 101.5 dB dynamic range (A-weighted) with 7.5 mW power consumption from a 3.3 V supply. The die area is 1.27 mm2. The fabricated delta-sigma modulator achieves the highest figure-of-merit among published high performance low power audio delta-sigma modulators.

This paper proposes an area efficient, low power, fractional CMOS bandgap reference (BGR) utilizing switched-current and current-memory techniques. The proposed circuit uses only one parasitic bipolar transistor and built-in current source to generate reference voltage. Therefore significant area and power reduction is achieved, and bipolar transistor device mismatch is eliminated. In addition, output reference voltage can be set to almost any value. The proposed circuit is designed and simulated in 0.18 µm CMOS process, and simulation results are presented. With a 1.6 V supply, the reference produces an output of about 628.5 mV, and simulated results show that the temperature coefficient of output is less than 13.8 ppm/ in the temperature range from 0 to 100. The average current consumption is about 8.5 µA in the above temperature range. The core circuit, including current source, opamp, current mirrors and switched capacitor filters, occupies less than 0.0064 mm2 (80 µm×80 µm).

This paper presents a technique to enhance in-band mismatch noise reduction of multi-stage second order Dynamic Element Matching (DEM) in multi-level ΔΣ Digital-to-Analog Converters (DACs). The presented technique changes an operational behavior of multi-stage DEM to reduce mismatch noise at in-band frequency. This change improves mismatch noise shaping performance for small amplitude input signals. Simulation result using 2-stage second order DEM and a third order 17-level ΔΣ modulator with 0.5% analog element mismatch shows 3.4 dB dynamic range improvement.

We propose an ultra low power watch-dog circuit with the use of MOSFETs operation under subthreshold characteristics. The circuit monitors the amount of the product degradation because the subthreshold current of MOSFET emulates the rate of the general chemical reaction. Its operation was verified with both SPICE simulation and the measurement of the prototype chip. The new circuit embedded in a tag attached to any product could dynamically monitor the degradation regardless of storage conditions.

A dynamic dither gain control technique for multi-level delta-sigma Digital-to-Analog Converters (DACs) using multi-stage Dynamic Element Matching (DEM) with a second order loop filter is proposed. The proposed technique provides improvement on the mismatch shaping performance through dynamic control of delta-sigma modulator dither gain. A large dither gain, which suppresses DEM operation dependency on input signal, is applied to delta-sigma modulator, when DEM loop filter output is greater than a designed reference. The design example using the proposed technique on a third order 17-level delta-sigma modulator with 3-stage cascaded DEM is shown in this paper. Simulation result with 1% analog segment mismatch shows over 10 dB improvement of THD+N performance under -50 dB amplitude input signal, compared to the case without the proposed technique.

A reference voltage buffer for a multibit/stage pipelined ADC is described, where a settling boost technique is used to improve the settling response of the pipelined stages. A 12 bit 18 MHz pipelined ADC with the buffer is designed and simulated based on a 0.35 µm CMOS process. According to simulation results, the power consumed by the reference voltage buffer is reduced by 33% compared to that without the settling boost technique.