N. Scott Barker's research while affiliated with University of Virginia and other places

This article presents a rigorous design method for a one-port-reflectionless filter with a Chebyshev response. In particular, we, for the first time, present inverter-coupled resonator filter topologies capable of having a Chebyshev response with zero reflection at all frequencies in theory. This work demonstrates a systematic approach for filter synthesis to find the normalized coupling (inverter) values without employing optimization methods or heuristic approaches. In addition, it provides closed-form design formulas in terms of a target frequency for the design of a one-port-reflectionless filter of coupled-line structure. We also present an exact approach to increase the reflectionless range of a distributed-element filter. Distributed-element bandpass filter structures formulated by this work are capable of producing a predefined canonical transmission response and a reflectionless feature over the entire frequency range at the same time, which has never been reported up to date. The presented topologies, synthesis results, and design methods have been applied to the design of second- and third-order filters for demonstration.

A proof-of-concept demonstration of on-wafer electronic calibration in the submillimeter-wave band (325—500 GHz) is presented. A GaAs Schottky diode shunting a coplanar transmission line is employed as an electronic standard that is tuned by bias applied through wafer probes. Error-corrected scattering parameter measurements, based on a Thru-Reflect-Line (TRL) calibration are used to characterize the on-wafer diode and establish it as a standard for electronic calibration. Subsequently, ensembles of measurements from a multiline TRL calibration and the diode calibration standard are performed and compared to assess the uncertainty associated with the two approaches. It is found that the error coefficients estimated using the electronic standard are in good agreement with those found from the multiline TRL calibration. Moreover, the electronic standard exhibits a significant reduction in uncertainty compared with the TRL standards, consistent with previous work showing that error in probe placement between measurements was a principle source of uncertainty for TRL-based calibration.

This article presents the first demonstration of a sub-100 nW CMOS wakeup receiver (WuRx) with envelope detector (ED)-first architecture that operates at multigigahertz frequencies. The 2.2 GHz S-band WuRx can operate in two modes that show a tradeoff between power consumption and RF sensitivity. In the low-power mode, the WuRx consumes 11.3 nW and achieves an RF sensitivity of -65 dBm. In the high-sensitivity mode, the WuRx consumes 28.2 nW and achieves a sensitivity of -68 dBm. Measurement results indicate that the WuRx architecture is robust to continuous-wave in-band interferers, with as large as -20 dB carrier-to-interferer ratio.

This letter presents a reconfigurable wake-up receiver, which obtains −106-dBm sensitivity with power consumption as low as 33 nW. Bit-level duty cycling provides 68-dB RF gain at sub- $\mu \text{W}$ average power consumption, improving sensitivity over other sub- $\mu \text{W}$ receivers. The receiver rejects interference using a compact RF MEMS filter and a fully automatic gain and offset control loop. Digital tuning of dc power, latency, and sensitivity provides high levels of flexibility to enable a wide variety of applications, spanning latency from 240 ms to 5 s, dc power consumption from 288 nW to 33 nW, and sensitivity from −106 dBm to −103 dBm. Three example modes are presented to highlight the range of this tuning.

This article proposes an advanced synthesis of the frequency-adaptive bandpass filter (FA-BPF) with constant absolute bandwidth (ABW). The proposed synthesis is based on the element-variable coupling matrix (EVCM), which is directly extracted from the classical filter polynomials. The extraction method is presented, investigated in detail, and confirmed by a set of numerical simulations. All frequency-dependent couplings between the resonators in an FA-BPF are uniquely modeled by the new coupling matrix, and the element variation of the EVCM directly accounts for the frequency tuning behavior of an FA-BPF. This one-to-one correspondence tackles the difficulty of the FA-BPF synthesis and design with a different center frequency tuning range (FTR), a different bandwidth (BW), and a different BW variation rate. This article also proposes the predefined coupling technique in the new synthesis. It allows both nonfrequency-dependent matrix and frequency-dependent matrix in an EVCM to be separately implemented in practice. For experimental demonstration, two four-pole/four-transmission zero (TZ) FA-BPFs with identical passband and constant ABW are implemented and then constitute a frequency-adaptive bandpass diplexer (FA-BPD) with two tunable channels that have identical passband and constant ABW. The measurement results exhibited performance superiority of the design and validated the proposed design method.

This paper presents the development of a wake-up receiver (WuRX) at nanowatt power levels for event-driven applications. This paper improves the state of the art, obtaining higher sensitivity than previous work in the 151.8- and 433-bands, low-power operation, and robustness to interference due to an integrated offset compensation algorithm operating without any external calibration. Simultaneous low-power operation and high sensitivity are achieved through a passive detector design based upon a terminal impedance boundary condition-based optimization of the detector dictated by the terminal impedances of the detector. This paper is implemented in a 130-nm CMOS process and obtains -76 dBm at the 151.8-MHz multi-use radio service (MURS) band and -71 dBm at the 433-MHz Industrial, Scientific and Medical (ISM) band with a total dc power draw of just 7.6 nW from 1.0- and 0.6-V supplies.

This paper proposes a general method to design the power divider (PD) with the arbitrary filtering response. The proposed model allows coupling matrix-based filter synthesis to be adopted in the Wilkinson PD (W-PD) design so that two-order, high-order, single-band, multiband, frequency-fixed, and frequency-tunable responses are all available for the W-PD. Meanwhile, benefiting from the generalized W-PD topology, the general model can be employed to design the PD with arbitrary termination impedances (TIs), arbitrary power division ratios (PDRs), and the highly favorable isolation. To demonstrate the proposed Wilkinson filtering PD (W-FPD), a series of resonator-coupled BPFs with open-end coupling feeding line and their corresponding coupling matrices are considered and applied to the W-FPD design. Accordingly, four frequency-fixed W-FPDs are designed to achieve four fully canonical responses with a full number of transmission zeros (TZs). In addition, two highly selective frequency-agile W-FPDs with the nearly constant absolute bandwidth (ABW) are designed to achieve the very wide frequency tuning range. The excellent simulation and measurement results experimentally validate that the proposed model can be utilized to realize W-FPD with two-order, high-order, single-band, multiband, equal, unequal, equal tunable, and unequal tunable filtering responses.