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A 0.18-μm CMOS wideband passive mixer fully integrated with baluns in IBM7HP process is reported. The mixer exhibits wideband operation, despite the intrinsic narrow-band magnitude balance of passive baluns. Very low DC offset, of less than 3 mV, is achieved without any DC cancellation circuits, due to high LO–RF isolation. At the RF frequency of 2.4 GHz, the combined IF differential outputs provide conversion loss (CL) of 7.5 dB, input 1 dB compression point (IP1dB) of 6.2 dBm, and input third-order intercept point (IIP3) of 15.5 dBm. This mixer exhibits broad-band RF impedance matching with reflection coefficient magnitude better than −9.6 dB through the RF frequency range from 1 to 12 GHz. The CL of 10.1–12.9 dB, IP1dB of 8.6–14.4 dBm, and IIP3 of 16–22.2 dBm are achieved at this frequency range for broad-band applications. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:23–27, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27226

We describe the fabrication of a screen printed disposable electrode system with integrated elements to allow for control of the working electrode temperature. The device has fully functional working, counter, and reference electrodes with underlying thermocouple and heating elements to allow feedback control of temperature. In our experiments, we determined that the accuracy of the temperature measurements on the electrode was within 0.5 °C over the temperature range of liquid water using a single universal calibration, and we demonstrated that the control system could maintain a setpoint temperature with a root mean squared error of 0.35 °C based on the indicated temperature. We used these electrodes to determine the temperature dependence of the diffusivity of ferricyanide ([Fe(CN)6]3−) ion using linear sweep voltammetry. The diffusion coefficient determined at 25 °C (0.85 × 10−5 cm2 s−1) was similar to other reported values in the literature, although our observed activation energy for diffusion (32.1 kJ mol−1) was significantly higher. Our observed temperature coefficient of −1.63 mV K−1 for the redox potential of the [Fe(CN)6]3−/[Fe(CN)6]4− couple is reasonably close to other reported values. The system shows promise for use in other disposable electrochemical diagnostic systems in which temperature control plays a key role, especially where perturbations or variations in ambient temperature or electrolyte rheological properties make feedback control necessary.

Recent advances in integrated circuit technology have produced highly integrated mixed-signal modules that include data acquisition, processing, storage, and wireless connectivity. Such System-on-Chip (SoC) modules are commercially available for a wide range of low power and portable applications, including industrial, consumer electronics, toys and gaming, renewable energy, sports and fitness, and medical applications. High performance analog and digital peripherals, multiple low power modes, and multiple transmission modes, make these modules customizable for various applications. Such modules could also provide low power and portability features to Doppler radar physiological sensors. In this paper we discuss advantages of using SoC's for Doppler radar physiological sensing, and compare performance of SoC transmission modes.

One of the challenges in Doppler radar systems for physiological monitoring is a large DC offset in baseband outputs. Typically, AC coupling is used to eliminate this DC offset. Since the physiological signals of interest include frequency content near DC, it is not desirable to simply use AC coupling on the radar outputs. While AC coupling effectively removes DC offset, it also introduces a large time delay and distortion. This paper presents the first DC coupled IQ demodulator printed circuit board (PCB) design and measurements. The DC coupling is achieved by using a mixer with high LO to RF port isolation, resulting in a very low radar DC offset on the order of mV. The DC coupled signals from the PCB radar system were successfully detected with significant LNA gain without saturation. Compared to the AC coupled results, the DC coupled results show great advantages of less signal distortion and more accurate rate estimation.

A low cost, low power Doppler radar occupancy sensor is developed by building a customized passive sensor node into a low power System-on-Chip (SoC) CC2530 RF transceiver. Experiment on the periodic moving mechanic target illustrates that this SoC based Doppler radar sensor is able to accurately detect the motion of the target under CW, modulated CW and packet operation modes. The study on sensitivity and power consumption under these modes indicates the most cost efficiency and power efficiency can be achieved by operating the sensor under packet mode with an optimum output power level.

A 2.4 GHz resistive ring mixer with on-chip baluns is fully integrated in 0.18µm IBM7HP process. This mixer exhibits broadband RF impedance matching with return loss better than −10 dB through the RF frequency range from 2 to 6 GHz. The conversion loss of 7.8 dB is achieved at the RF frequency 2.4 GHz. This mixer provides 6 dBm of the input P1dB, and 13.4 dBm of the input IP3 at the operating RF frequency. This mixer is the first reported double-balanced resistive mixer with integrated RF and LO baluns. This mixer has a very compact layout due to the absence of the matching circuits, and is suitable for homodyne and heterodyne transceiver architectures for wireless applications.

This paper describes a wide-band resistive ring mixer fully integrated in 0.25μm CMOS process. This mixer exhibits broadband RF impedance matching with return loss better than −10 dB from 2.2 to 8.3 GHz, and better than −15 dB from 3 to 6.2 GHz. The best conversion loss (CL) of 6.4 dB is achieved at 3.2 GHz. The input P1dB is better than 4 dBm, and the IIP3 is better than 11.4 dBm over the entire RF bandwidth of 2 – 9 GHz. Compared to other published CMOS wide-band resistive mixers, this mixer achieves the best linearity between 2 and 9 GHz. In addition, with a small gate bias a moderate CL is achieved at very low LO power levels.

The simultaneous removal of organic and nitrogen and molecular weight distribution (MWD) of residual soluble chemical oxygen demand (RSCOD) in final effluent were investigated using entrapped mixed microbial cells (EMMC) and conventional activated sludge processes. Two different types of processes using EMMC carriers demonstrated better organic and nitrogen removal performance because of the high solids retention time (SRT) compared with the activated sludge process. Regarding the RSCOD, the longer SRT process (EMMC) was affected by reducing the hydraulic retention time, resulting in the increase of high-molecular-weight materials. On the other hand, reducing the aeration period had significantly affected the MWD in the shorter SRT process (activated sludge), resulting in an increase of low-molecular-weight materials.

The current revolution in wireless communications has created a critical need for engineering graduates in this field, and has sparked renewed interest in RF/microwave circuits and systems courses. The University of Hawaii has developed a discovery-based, graduate-level laboratory course in active microwave electronics that has several distinguishing features compared to conventional graduate-level microwave courses: (1) instead of a traditional lecture format, the course is taught in studio mode, in which all student activities take place in a research laboratory that has separate stations for computer-aided design, fabrication, and measurement; (2) the instructor provides minimal guidance to the students, and instead relies on group discussions to elicit critical design methodologies; (3) the design projects are not typical canned experiments, but rather open-ended projects that emphasize self discovery. We present one of the projects from this course. Each student was given the mission of designing, fabricating, measuring, and modeling a 10-GHz maximum-gain amplifier. While seemingly a straightforward objective, the students found many obstacles along the way that provided invaluable opportunities for self discovery.

A retrodirective array using self-oscillating mixers (SOMs) is presented. SOMs allow for easier implementation of larger two-dimensional arrays by eliminating the complex local-oscillator (LO) feed structure. A four-element linear retrodirective array using SOMs is demonstrated at a LO frequency of 8.87 GHz. Each element is successfully phased locked at the LO frequency while 33 dB of isolation between adjacent elements is measured at the RF frequency. The LO power generated by a single SOM element at the fundamental frequency is +3 dBm. Retrodirectivity is successfully observed for scattering angles of -30/spl deg/, 0/spl deg/, and +15/spl deg/.