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Wireless sensing networks (WSNs) collect analog information transduced into the form of a voltage or current. This data is typically converted into a digital representation of the value and transmitted wirelessly using various modulation techniques. As the available power and size is limited for wireless sensor nodes in many applications, a medium resolution Analog-to-Digital Converter (ADC) is proposed to convert a sensed voltage with moderate speeds to lower power consumption. Specifications also include a rail-to-rail input range and minimized errors associated with offset, gain, differential nonlinearity, and integral nonlinearity. To achieve these specifications, an 8-bit successive approximation register ADC is developed which has a conversion time of nine clock cycles. This ADC features a charge scaling array included to achieve minimized power consumption and area by reducing unit capacitance in the digital-to-analog converter. Furthermore, a latched comparator provides fast decisions utilizing positive feedback. The ADC was designed and simulated using Cadence Virtuoso with parasitic extraction over expected operating temperature range of 0 – 85°C. The design was fabricated using TSMC’s 65 nanometer RF GP process and tested on a printed circuit board to verify design specifications. The measured results for the device show an offset and gain error of +7 LSB and 31.1 LSB, respectively, and a DNL range of -0.9 LSB to +0.8 LSB and an INL range of approximately -4.6 LSB to +12 LSB. The INL is much improved in regard to the application of the temperature sensor. The INL for this region of interest is from -3.5 LSB to +2.8 LSB.

Abstract: Nanoscale optical and mechanical resonators store energy in a way characterized by a sharp resonance frequency, and through interaction with their surroundings offer a path to the next generation of sensitive measurement tools. In this thesis we investigate a particular geometry of nanofabricated devices-that of monolithically fabricated optical microdisks and nanomechanical resonators, in which the optical microdisk operates as a high-gain amplifier of the mechanical resonator's position. We began the study with nanoscale silicon microdisks and cantilevers fabricated with a commercial photolithography process for silicon photonics, and used the optomechanical interaction between the cantilevers and optical microdisks to demonstrate readout of the mechanical motion to the fm Hz^-0.5 precision level. This approach has enabled thermally limited readout of forces on the cantilever to 130 +- 40 aN Hz^-0.5 at room temperature, optimized by their nanometer-sized geometry and femtogram-scale masses. We then explored the possibility of using these cantilevers for fundamental quantum measurements of phonon number, and although we concluded the cantilever measurement lacked the necessary characteristics, we developed a framework for characterizing the type of optomechanical coupling exhibited by an optomechanical device. Continuing on resonator development, we switched to fabricating similar geometry optomechanical devices from silicon nitride, an insulating material used in semiconductor fabrication, known to enable a high quality factor mechanical resonator geometry termed nanostrings. Using a fiber-waveguide coupling technique we were able to optomechanically measure picogram-scale nanostring devices down to temperatures below 1 K, finding mechanical quality factors of 10^6, while exhibiting less optically-induced heating than similar silicon devices. While the optical microdisks enable high-precision readout of mechanical motion, they more generally measure refractive index changes. Using aqueously submerged silicon nitride microdisks, we were able to measure LiCl induced refractive index changes down to the 10^-6 level. Finally, we carry out a discussion and review on the subject of digital signal processing. Although appearing unrelated, the techniques covered in Chapter 7 underline every single experimental result covered in this thesis. With an understanding of digital signals, flexible and well adapted measurement protocols can be constructed without being stuck relying on the output of fixed-pipeline measurement tools.

Over the past few years, there has been a growing need for wireless communications with higher data rates and ubiquitous coverage, and these must be achieved at reduced cost and with a lower carbon footprint. This evolution in wireless demand places a big burden on transmitter architectures. The need for higher efficiency has stimulated research into the potential replacement of current linear power amplifiers (PAs) by switch mode power amplifiers (SMPAs) at cellular frequencies. The radio frequency (RF) PA currently accounts for a significant part of the cost, and most of the power requirements of a typical wireless base station. This research is focused on the modulation and up-conversion circuits for generating the SMPA drive signals. The switched (‘on’/‘off’) nature of the amplifier drive signal creates an opportunity for an all-digital solution removing traditional analog components such as the digital to analog converters, reconstruction filters, quadrature modulator and local oscillators. Digital signal processing techniques used for signal modulation are extended to digital up-conversion to generate suitable drive signals for the SMPA. In this thesis, a sigma-delta (ΣΔ) based technique is used to embed a complex modulation scheme such as OFDM into a single ‘on’-‘off’ bit stream.