Novel RF/Microwave Circuits And Systems for Lab on-Chip/on-Board Chemical Sensors

Recent research focuses on expanding the use of RF/Microwave circuits and systems to include multi-disciplinary applications. One example is the detection of the dielectric properties of chemicals and bio-chemicals at microwave frequencies, which is useful for pharmaceutical applications, food and drug safety, medical diagnosis and material characterization. Dielectric spectroscopy is also quite relevant to detect the frequency dispersive characteristics of materials over a wide frequency range for more accurate detection. In this dissertation, on-chip and on-board solutions for microwave chemical sensing are proposed. An example of an on-chip dielectric detection technique for chemical sensing is presented. An on-chip sensing capacitor, whose capacitance changes when exposed to material under test (MUT), is a part of an LC voltage-controlled oscillator (VCO). The VCO is embedded inside a frequency synthesizer to convert the change in the free runing frequency frequency of the VCO into a change of its input voltage. The system is implemented using 90 nm CMOS technology and the permittivities of MUTs are evaluated using a unique detection procedure in the 7-9 GHz frequency range with an accuracy of 3.7% in an area of 2.5 × 2.5 mm^2 with a power consumption of 16.5 mW. The system is also used for binary mixture detection with a fractional volume accuracy of 1-2%. An on-board miniaturized dielectric spectroscopy system for permittivity detec- tion is also presented. The sensor is based on the detection of the phase difference be- tween the input and output signals of cascaded broadband True-Time-Delay (TTD) cells. The sensing capacitor exposed to MUTs is a part of the TTD cell. The change of the permittivity results in a change of the phase of the microwave signal passing through the TTD cell. The system is fabricated on Rogers Duroid substrates with a total area of 8 × 7.2 cm2. The permittivities of MUTs are detected in the 1-8 GHz frequency range with a detection accuracy of 2%. Also, the sensor is used to extract the fractional volumes of mixtures with accuracy down to 1%. Additionally, multi-band and multi-standard communication systems motivate the trend to develop broadband front-ends covering all the standards for low cost and reduced chip area. Broadband amplifiers are key building blocks in wideband front-ends. A broadband resistive feedback low-noise amplifier (LNA) is presented using a composite cross-coupled CMOS pair for a higher gain and reduced noise figure. The LNA is implemented using 90 nm CMOS technology consuming 18 mW in an area of 0.06 mm2. The LNA shows a gain of 21 dB in the 2-2300 MHz frequency range, a minimum noise figure of 1.4 dB with an IIP3 of -1.5 dBm. Also, a four-stage distributed amplifier is presented providing bandwidth extension with 1-dB flat gain response up to 16 GHz. The flat extended bandwidth is provided using coupled inductors in the gate line with series peaking inductors in the cascode gain stages. The amplifier is fabricated using 180 nm CMOS technology in an area of 1.19 mm2 achieving a power gain of 10 dB, return losses better than 16 dB, noise figure of 3.6-4.9 dB and IIP3 of 0 dBm with 21 mW power consumption. All the implemented circuits and systems in this dissertation are validated, demonstrated and published in several IEEE Journals and Conferences

A PLL-Based Frequency Shift Measurement System for Chemical and Biological Sensing

A PLL-based frequency shift measurement system for chemical and biological sensing was developed and implemented in the form of two discrete electronic assemblies. One of the assemblies consists of a VCO which contains a microwave resonator sensor while the other assembly contains commercially available PLL and MCU devices, as well as various other discrete components. When mated together, a PLL-based frequency synthesizer is realized, the output frequency of which is ~4.5 GHz. The system is used to measure the frequency shift exhibited by the frequency synthesizer when several commonly-known chemical substances are applied to the microwave resonator sensor test fixture. Because the amount of measured frequency shift is proportional to the dielectric constant of a given material under test (MUT), this system can potentially be used as part of a chemical identification system. This measurement system is also attractive in that it represents a stand-alone or 'self-contained' system which does not require usage of any additional expensive and bulky electronic diagnostic equipment such as a network analyzer or signal generator, making it a relatively inexpensive and portable solution. Attempts to use the system to measure frequency shift resulting from application of various common chemical substances to the sensor fixture results in derivation of dielectric constant values which hold very close agreement (+/-2%) to the published/theoretical dielectric constant values for each respective chemical substance

Design of Integrated Microwave Frequency Synthesizer-Based Dielectric Sensor Systems

Dielectric sensors have several biomedical and industrial applications where they are used to characterize the permittivity of materials versus frequency. Characterization at RF/microwave frequencies is particularly useful since many chemicals/bio-materials show significant changes in this band. The potential system cost and size reduction possible motivates the development of fully integrated dielectric sensor systems on CMOS with high sensitivity for point-of-care medical diagnosis platforms and for lab-on-chip industrial sensors. Voltage-controlled oscillator (VCO)-based dielectric sensors embed the sensing capacitor within the excitation VCO to allow for self-sustained measurement of the material under test (MUT)-induced frequency shift with simple and precise readout circuits. Despite their advantages, VCO-based sensors have several design challenges. First, low frequency noise and environmental variations limit their sensitivity. Also, these systems usually place the VCO in a frequency synthesizer to control the sample excitation frequency which reduces the resolution of the read-out circuitry. Finally, conventional VCO-based systems utilizing LC oscillators have limited tuning range, and can only characterize the real part of the permittivity of the MUT. This dissertation proposes several ideas to: 1) improve the sensitivity of the system by filtering the low frequency noise and enhance the resolution of the read-out circuitry, 2) improve the tuning range, and 3) enable complex dielectric characterization in VCO/synthesizer-based dielectric spectroscopy systems. The first prototype proposes a highly-sensitive CMOS-based sensing system for permittivity detection and mixture characterization of organic chemicals at microwave frequencies. The system determines permittivity by measuring the frequency difference between two VCOs; a sensor oscillator with an operating frequency that shifts with the change in tank capacitance due to exposure to the MUT and a reference oscillator insensitive to the MUT. This relative measurement approach improves sensor accuracy by tracking frequency drifts due to environmental variations. Embedding the sensor and reference VCOs in a fractional-N phase-locked loop (PLL) frequency synthesizer enables material characterization at a precise frequency and provides an efficient material-induced frequency shift read-out mechanism with a low-complexity bang-bang control loop that adjusts a fractional frequency divider. The majority of the PLL-based sensor system, except for an external fractional frequency divider, is implemented with a 90 nm CMOS prototype that consumes 22 mW when characterizing material near 10 GHz. Material-induced frequency shifts are detected at an accuracy level of 15 ppmrms and binary mixture characterization of organic chemicals yield maximum errors in permittivity of <1.5%. The second prototype proposes a fully-integrated sensing system for wideband complex dielectric detection of MUT. The system utilizes a ring oscillator-based PLL for wide tuning range and precise control of the sensor's excitation frequency. Characterization of both real and imaginary MUT permittivity is achieved by measuring the frequency difference between two VCOs: a sensing oscillator, with a frequency that varies with MUT-induced changes in capacitance and conductance of a delay-cells' sensing capacitor loads, and a MUT-insensitive reference oscillator that is controlled by an amplitude-locked loop (ALL). The fully integrated system is fabricated in 0.18 μm CMOS, and occupies 6.25 mm2 area. When tested with common organic chemicals (ε`r < 30), the system operates between 0.7-6 GHz and achieves 3.7% maximum permittivity error. Characterization is also performed with higher ε`r water-methanol mixtures and phosphate buffered saline (PBS) solutions, with 5.4% maximum permittivity error achieved over a 0.7-4.77 GHz range

Novel RF CMOS Integrated Circuits and Systems for Broadband Dielectric Spectroscopy

Broadband dielectric spectroscopy has proven to be a valuable technique for characterization of chemicals and biomaterials. It has the great potential to become an indispensable and cost-effective tool in point-of-care medical applications due to its label-free and non-invasive operation. However, most of the existing dielectric spectroscopy instruments require bulky, heavy and expensive measurement set-up, restricting their use to only special applications in industry and laboratories. Therefore, integrated dielectric spectroscopy on silicon capable of direct detection of chemicals/biomaterials' complex permittivity can yield significant cost and size reduction, system integration, portability, enormous processing, and high throughput. A CMOS wideband dielectric spectroscopy system is proposed for chemical and biological material characterization. The complex permittivity detection is performed using a configurable harmonic-rejecting receiver capable of indirectly measuring the complex admittance of sensing capacitor exposed to the material-under-test (MUT) and subject to RF signal excitation with a frequency range of 0.62-10 GHz. The sensing capacitor is embedded in a voltage divider topology with a fixed capacitor and the relative variations in the magnitude and phase of the voltages across the capacitors are used to find the real and imaginary parts of the permittivity. The sensor achieves an rms permittivity error of less than 1% over the entire operation bandwidth. Using a sub-harmonic mixing scheme, the system can perform complex permittivity measurements from 0.62 to 10 GHz while requiring an input signal source with frequency range of only from 5 to 10 GHz. Thereby, the permittivity measurement system can be easily made self-sustained by implementing a 5-10 GHz frequency synthesizer on the same chip. One of the key building blocks in such a frequency synthesizer is the voltage-controlled oscillator (VCO) which has to cover an octave of frequency range. A novel low-phase-noise wide-tuning range VCO is presented using a triple-band LC resonator. The implemented VCO in 0.18μm CMOS technology achieves a continuous tuning range of 86.7% from 5.12 GHz to 12.95 GHz while drawing 5 to 10 mA current from 1-V supply. The measured phase noise at 1 MHz offset from carrier frequencies of 5.9, 9.12 and 12.25 GHz is -122.9, -117.1 and -110.5 dBc/Hz, respectively. Also, a dual-band quadrature voltage-controlled oscillator (QVCO) is presented using a transformer-based high-order LC-ring resonator which inherently provides quadrature signals without requiring noisy coupling transistors as in traditional approaches. The proposed resonator shows two possible oscillation frequencies which are exploited to realize a wide-tuning range QVCO employing a mode-switching transistor network. Due to the use of transformers, the oscillator has minimal area penalty compared to the conventional designs. The implemented prototype in a 65-nm CMOS process achieves a continuous tuning range of 77.8% from 2.75 GHz to 6.25 GHz while consuming 9.7 to 15.6 mA current from 0.6-V supply. The measured phase noise figure-of-merit (FoM) at 1 MHz offset ranges from 184 dB to 188.2 dB throughout the entire tuning range. The QVCO also exhibits good quadrature accuracy with 1.5º maximum phase error and occupies a relatively small silicon area of 0.35 mm^2

A high sensitivity and low power circuit for the measurement of abnormal blood cell levels

This paper describes a technique to detect blood cell levels based on the time-period modulation of a relaxation oscillator loaded with an Inter Digitated Capacitor (IDC). A digital readout circuit has been proposed to measure the time-period difference between the two oscillators loaded with samples of healthy and (potentially) unhealthy blood. A prototype circuit was designed in 65nm CMOS technology and post-layout simulations shows 15.25aF sensitivity. The total circuit occupies 2184µm2 silicon area and consumes 216µA from a 1V power supply

Advances in Filter Miniaturization and Design/Analysis of RF MEMS Tunable Filters

The main purpose of this dissertation was to address key issues in the design and analysis of RF/microwave filters for wireless applications. Since RF/microwave filters are one of the bulkiest parts of communication systems, their miniaturization is one of the most important technological challenges for the development of compact transceivers. In this work, novel miniaturization techniques were investigated for single-band, dual-band, ultra-wideband and tunable bandpass filters. In single-band filters, the use of cross-shaped fractals in half-mode substrate-integrated-waveguide bandpass filters resulted in a 37 percent size reduction. A compact bandpass filter that occupies an area of 0.315 mm2 is implemented in 90-nm CMOS technology for 20 GHz applications. For dual-band filters, using half-mode substrate-integrated-waveguides resulted in a filter that is six times smaller than its full-mode counterpart. For ultra-wideband filters, using slow-wave capacitively-loaded coplanar-waveguides resulted in a filter with improved stopband performance and frequency notch, while being 25 percent smaller in size. A major part of this work also dealt with the concept of 'hybrid' RF MEMS tunable filters where packaged, off-the-shelf RF MEMS switches were used to implement high-performance tunable filters using substrate-integrated-waveguide technology. These 'hybrid' filters are very easily fabricated compared to current state-of-the-art RF MEMS tunable filters because they do not require a clean-room facility. Both the full-mode and half-mode substrate-integrated waveguide tunable filters reported in this work have the best Q-factors (93 - 132 and 75 - 140, respectively) compared to any 'hybrid' RF MEMS tunable filter reported in current literature. Also, the half-mode substrate-integrated waveguide tunable filter is 2.5 times smaller than its full-mode counterpart while having similar performance. This dissertation also presented detailed analytical and simulation-based studies of nonlinear noise phenomena induced by Brownian motion in all-pole RF MEMS tunable filters. Two independent mathematical methods are proposed to calculate phase noise in RF MEMS tunable filters: (1) pole-perturbation approach, and (2) admittance-approach. These methods are compared to each other and to harmonic balance noise simulations using the CAD-model of the RF MEMS switch. To account for the switch nonlinearity in the mathematical methods, a nonlinear nodal analysis technique for tunable filters is also presented. In summary, it is shown that output signal-to-noise ratio degradation due to Brownian motion is maximum for low fractional bandwidth, high order and high quality factor RF MEMS tunable filters. Finally, a self-sustained microwave platform to detect the dielectric constant of organic liquids is presented in this dissertation. The main idea is to use a voltage- controlled negative-resistance oscillator whose frequency of oscillation varies according to the organic liquid under test. To make the system self-sustained, the oscillator is embedded in a frequency synthesizer system, which is then digitally interfaced to a computer for calculation of dielectric constant. Such a system has potential uses in a variety of applications in medicine, agriculture and pharmaceuticals

Circuits and Systems for On-Chip RF Chemical Sensors and RF FDD Duplexers

Integrating RF bio-chemical sensors and RF duplexers helps to reduce cost and area in the current applications. Furthermore, new applications can exist based on the large scale integration of these crucial blocks. This dissertation addresses the integration of RF bio-chemical sensors and RF duplexers by proposing these initiatives. A low power integrated LC-oscillator-based broadband dielectric spectroscopy (BDS) system is presented. The real relative permittivity ε’r is measured as a shift in the oscillator frequency using an on-chip frequency-to-digital converter (FDC). The imaginary relative permittivity ε”r increases the losses of the oscillator tank which mandates a higher dc biasing current to preserve the same oscillation amplitude. An amplitude-locked loop (ALL) is used to fix the amplitude and linearize the relation between the oscillator bias current and ε”r. The proposed BDS system employs a sensing oscillator and a reference oscillator where correlated double sampling (CDS) is used to mitigate the impact of flicker noise, temperature variations and frequency drifts. A prototype is implemented in 0.18 µm CMOS process with total chip area of 6.24 mm^2 to operate in 1-6 GHz range using three dual bands LC oscillators. The achieved standard deviation in the air is 2.1 ppm for frequency reading and 110 ppm for current reading. A tunable integrated electrical balanced duplexer (EBD) is presented as a compact alternative to multiple bulky SAW and BAW duplexers in 3G/4G cellular transceivers. A balancing network creates a replica of the transmitter signal for cancellation at the input of a single-ended low noise amplifier (LNA) to isolate the receive path from the transmitter. The proposed passive EBD is based on a cross-connected transformer topology without the need of any extra balun at the antenna side. The duplexer achieves around 50 dB TX-RX isolation within 1.6-2.2 GHz range up to 22 dBm. The cascaded noise figure of the duplexer and LNA is 6.5 dB, and TX insertion loss (TXIL) of the duplexer is about 3.2 dB. The duplexer and LNA are implemented in 0.18 µm CMOS process and occupy an active area of 0.35 mm^2

A Portable Microwave Interferometry Sensor for Permittivity Detection Based on CCMRC

© 2013 IEEE. A portable microwave complex permittivity sensor based on the interferometry configuration is proposed. A complementary compact microstrip resonant cell (CCMRC) is applied as the sensitive element, which converts the dielectric information of the material under test (MUT) into the phase variations of its transmission coefficient. A miniaturized interferometry platform based on a down-converting mixer further translates the phase change into DC output voltage variation, which can be readily recorded with a direct readout circuit. In this context, expensive and bulky vector network analyzer is no longer needed, thereby leading to a low hardware cost. With comprehensive theoretical analysis, the material permittivity is simply extracted using a specific extrapolation algorithm. As a proof of concept, several different solid material samples with known permittivity values are used to verify the devised detection system

A PLL-Based Frequency Shift Measurement System for Chemical and Biological Sensing

A PLL-based frequency shift measurement system for chemical and biological sensing was developed and implemented in the form of two discrete electronic assemblies. One of the assemblies consists of a VCO which contains a microwave resonator sensor while the other assembly contains commercially available PLL and MCU devices, as well as various other discrete components. When mated together, a PLL-based frequency synthesizer is realized, the output frequency of which is ~4.5 GHz. The system is used to measure the frequency shift exhibited by the frequency synthesizer when several commonly-known chemical substances are applied to the microwave resonator sensor test fixture. Because the amount of measured frequency shift is proportional to the dielectric constant of a given material under test (MUT), this system can potentially be used as part of a chemical identification system. This measurement system is also attractive in that it represents a stand-alone or 'self-contained' system which does not require usage of any additional expensive and bulky electronic diagnostic equipment such as a network analyzer or signal generator, making it a relatively inexpensive and portable solution. Attempts to use the system to measure frequency shift resulting from application of various common chemical substances to the sensor fixture results in derivation of dielectric constant values which hold very close agreement (+/-2%) to the published/theoretical dielectric constant values for each respective chemical substance