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A complementary metal oxide semiconductor (CMOS) voltage‐controlled oscillator (VCO) using a tail current source modulated with the output frequency is presented to achieve low phase noise with low power consumption at the K‐band. Differentially modulated current sources, which reduce flicker noise by the feedback of the VCO outputs, contribute to an overall reduction in the phase noise of the VCO using the electromagnetic‐based fully symmetrical design. The proposed LC VCO with a 3‐bit switched capacitor bank for a wide tuning range was fabricated on the size of 0.4 × 0.57 mm2 using a 65‐nm CMOS process. The measurement results of the proposed VCO showed a frequency tuning range from 22.57 to 25.3 GHz, and a phase noise of −108.48 dBc/Hz at a 1‐MHz offset frequency with a power consumption of 8.27 mW at a supply voltage of 1.2 V. The calculated figure of merit (FoM) and FoM with the tuning range were −186.48 and −187.67 dBc/Hz, respectively. [ABSTRACT FROM AUTHOR]

A folded dipole antenna using an artificial magnetic conductor (AMC) structure is proposed to improve the frequency bandwidth and reduce the size of the antenna on a chip. To change the distribution of the electromagnetic (EM) field, the proposed AMC structure shaped with square‐in‐square rings (SSRs) is arranged along the radiating metal of the folded dipole antenna and implemented on the lowermost metal layer of the backend oxide layers (BEOLs) between the radiating metal of the top layer of the BEOL and the ground plane of the bottom of the substrate. The SSR of the proposed antenna‐on‐chip (AoC) widens the frequency bandwidth by varying the electrical length to the ground and reduces the physical size of the radiating metal by increasing the effective permittivity. The 3D EM‐wave simulation shows that the proposed AMC structure changes the distribution of EM‐wave in the BEOL and Si substrate such that more EM fields are condensed around the radiating metal and the electrical length to the ground is nonuniform and longer. The AoC with the proposed AMC structure was fabricated using a 65‐nm standard complementary metal‐oxide semiconductor process with one‐poly and nine‐metal. Compared with the conventional 150‐GHz antenna that was implemented on the same die, the proposed differential antenna was measured to be a −10 dB bandwidth of 46 GHz, with a 1.12‐times improvement, and a size reduction of 20.4%. The measured gain of the proposed antenna was −5.99 dBi including the passive balun with an insertion loss of −1.36 dB in simulation. [ABSTRACT FROM AUTHOR]

Frequency-modulated continuous wave (FMCW) radar system synchronization using external clock signals can cause repeated Range-Doppler (R-D) map corruption when clock signal asynchronization problems occur between the transmitter and receiver. In this paper, we propose a signal processing method for the reconstruction of the corrupted R-D map owing to the FMCW radar's asynchronization. After calculating the image entropy for each R-D map, the corrupted ones are extracted and reconstructed using the normal R-D maps acquired before and after the individual maps. To verify the effectiveness of the proposed method, three target detection experiments were conducted: a human target detection in an indoor environment and a wide place and a moving bike-rider target detection in an outdoor environment. The corrupted R-D map sequence of observed targets in each case was reconstructed properly and showed the validity by comparing the map-by-map range and speed changes in the detected target with the ground-truth information of the target. [ABSTRACT FROM AUTHOR]

A complementary metal–oxide–semiconductor (CMOS) detector array is proposed to improve the sub-terahertz imaging resolution for objects in the conveyor belt system. The image resolution is limited to the implemented configuration, such as the wide spacing in the detector array, the high conveyor belt speed, and the slow response of the signal conditioning block. The proposed array can improve the image resolution in the direction perpendicular to the movement of the belt, which is determined by the size and interval of the detector pixel, by configuring the array into two replaceable columns located at the misaligned horizontal positions. Replaceable detector unit pixels are individually attached to the motherboard after measuring and evaluating the detection performance to construct the proposed array. The intensities of 32 detector pixels placed under the conveyor belt with a width of 160 mm were initially calibrated in every image, including the beam pattern of 0.2 THz signals generated from the gyrotron. The image resolution of the perpendicular direction obtained from the proposed array was measured to be approximately 5 mm at a conveyor belt speed of 16 mm/s, demonstrating a 200% improvement in resolution compared to the conventional linear array under the same conditions. [ABSTRACT FROM AUTHOR]

This study proposed a method for distinguishing the baseband signal for each frequency in two‐tone radar systems using the difference in the number of peaks of the envelope detected signal. The proposed method is based on the characteristic that the baseband signal for each frequency exhibits a different number of peaks, depending on the operating frequency, at a fixed sampling frequency in data acquisition. The phase difference between the transmitting and receiving signals for each frequency can be obtained using envelope detection of the baseband signals in two‐tone radar systems, and the proposed method can effectively match the phase difference and operating frequency without using additional controls and synchronization. This simplifies the procedure to estimate the absolute range up to the maximum unambiguous range, corresponding to a phase difference of 2π. Measurement results demonstrate that the absolute range, using a two‐tone radar with a frequency spacing of 150 MHz, can detect the distance with an accuracy of 97.8% up to the maximum unambiguous range using the proposed method. [ABSTRACT FROM AUTHOR]

A multiphase continuous-wave (MPCW) Doppler radar with a multiarc circle fitting (MACF) algorithm is proposed for improving the accuracy of small periodic displacement measurements. In the proposed radar, local oscillator (LO) signals with different phases are incident to multiple I/Q mixers, to simultaneously generate multiarcs for small periodic motions. The multiarcs obtained from the synchronized data are used in the circle fitting method to provide dc offset compensation, for accurate phase demodulation. The proposed MACF algorithm, based on the Levenberg–Marquardt method, can more precisely compensate for the dc offset by combining multiarcs generated from the proposed radar. A 5.8-GHz MPCW Doppler radar module with four-phased LO signals is implemented as a demonstration. The small periodic displacement of a metal plate on a single-axis linear stage is measured using the proposed radar module and algorithm. Compared with conventional CW Doppler radar using a single arc, measurement results using the proposed radar show that the root-mean-square error (RMSE) can be effectively decreased in the periodic motion from 1 to 2 mm, at distances from 30 to 60 cm. The RMSE is reduced by more than 33% for a peak-to-peak displacement of 1 mm at a distance of 60 cm. [ABSTRACT FROM AUTHOR]

A CMOS plasmon detector with a low‐gain buffer amplifier, which enhances the characteristics of the detector core, is proposed for improving the performance of THz imaging systems. A high voltage gain (AV) of the main amplifier integrated with the detector improves the voltage responsivity (RV) but not the performances of the detector core itself. The increase in the ratio of the RV to the noise‐equivalent power (NEP) in the proposed detector with a low‐gain buffer can improve the signal‐to‐noise ratio (SNR) of the THz images. The proposed detector with a − 1.5 dB AV buffer amplifier is fabricated by TSMC 0.25 μm CMOS technology and measured to have the RV of 357.1 kV/W and NEP of 57.3 pW/√Hz at the gate bias of 0.17 V for 0.2 THz input signals. The measurement results indicate that the proposed detector has an RV lower than that of a detector with an AV of 11.2 dB exhibiting a similar NEP. The obtained 0.2 THz raster scanning images show that the image SNR can be improved by 14.8 dB using in the proposed detector. [ABSTRACT FROM AUTHOR]

A CMOS detector with a customized capacitor is proposed to improve the detection performance for terahertz imaging systems. The proposed gate-drain capacitor is formed based on the bolt-wrench shape integrated into the layout design of the detector core. The proposed capacitor is implemented using a metal-insulator-metal stack in the backend oxide layer of the TSMC 0.25-μm CMOS technology. The detector using the customized capacitor exhibits an 18% improvement in the voltage responsivity simulation compared to the detector using the capacitor in the process design kit (PDK). The measurement results of the detector, including the integrated antenna and amplifiers, indicate a voltage responsivity of 2.99 MV/W and a noise-equivalent power of 46.3 pW/ √Hz. The 200-GHz images obtained using the proposed detector demonstrate a 30% correlation improvement with the sample compared to the images obtained using the detector with the PDK capacitor. [ABSTRACT FROM AUTHOR]

An inverse class E frequency doubler is proposed to improve power conversion efficiency by using a transmission‐line‐based notch filter. The notch filter implemented using a transmission line is used at the output network in the doubler to suppress both fundamental and high‐order harmonic signals by a switching‐mode operation. A fourth harmonic signal is also reduced by using the quarter‐wavelength transmission line at the output network. Two frequency doublers with the proposed output network are optimized at different input power values and implemented on an FR4 PCB. In the measurement results, the doubler optimized at a low driving power shows a power conversion efficiency of 26.3% and an output power of 11.2 dBm for an input power of 11.5 dBm. The signal rejection levels of the low‐power optimized doubler power are −32, −40.1, and −31.7 dBc at the fundamental frequency, third harmonics, and fourth harmonics, respectively. The doubler optimized at a high driving power shows a power conversion efficiency of 24.6%, an output power of 13.7 dBm, and a signal rejection of less than −29.8 dBc, respectively. [ABSTRACT FROM AUTHOR]

A continuous‐wave (CW) Doppler radar using two‐tone frequencies is presented for the measurement of short‐range distance. The envelope detection method is proposed to discriminate each frequency signal in the output waveform of the two‐tone CW Doppler radar sensor. The phase difference in each frequency is obtained from the nonlinearly demodulated I/Q baseband signals, following calibration of the I/Q imbalance and DC offset voltages. The absolute distance is derived from the phase differences at the two‐tone frequencies with a 100 MHz spacing. The measurement results in the two‐tone radar system show a maximum error of 2.5 cm in the 20 to 50 cm distance range. [ABSTRACT FROM AUTHOR]

A V-band CMOS frequency tripler with efficient input–output, and interstage matching networks is proposed to improve the output power and conversion efficiency. The interstage matching network, located between a tripler-core and a buffer amplifier, simultaneously performs the impedance matching of a desired third harmonic signal and the filtering of unwanted fundamental and even harmonic signals, without an additional power loss in a small area. Wideband operation and differential signal balance characteristics are achieved at the input and output by using a transformer-based balun with a compensation capacitor. The proposed tripler was implemented in a size of 0.476 mm2 using the TSMC 65-nm CMOS technology. Measurement results show a saturated output power of 6.4 dBm with a harmonic rejection of 37 dBc for an input power of 10 dBm at 59.4 GHz. The maximum conversion efficiency is 3.92% with an input power of 6.5 dBm at 59.4 GHz. [ABSTRACT FROM AUTHOR]

The heartbeat detection using the scaling function of Wavelet transform is proposed for a Doppler radar sensor. The conventional methods such as the fast‐Fourier transform and the autocorrelation show the respiration rate and the heartbeat from the raw data of the radar sensors acquiring for a sufficient sampling time. The methods have the limit to detect the biometric information that varies with real‐time because they only show the overall statistical information of the sampled data. In the proposed method, the scaling function in the Daubechies wavelet transform can be used to accurately find out the periodicity of radar signals for detecting heartbeat varying in real‐time. The results of the signal processing using the radar signals acquired for 3 min results show that the proposed method lowered a mean error rate of 2.5% and a SD of 2.0% compared with the method using the wavelet function. The proposed method in the measurement for 1 minute using the radar sensor also showed the lowest mean error rate of 3.8% and the low SD of 3.2% using the contact sensor as the reference among various signal processing methods including auto‐correlation and peak detection with filtering. [ABSTRACT FROM AUTHOR]

A method of measuring the amplitude ratios and phase differences among the same RF output signals from multiple ports at the same frequency is proposed. A power-combining module is used to couple multiple signals vectorially from the ports. In the proposed method, the amplitude ratios among the RF signals from multiple ports are calculated using the output power of the module to which only one port is connected, and using the S-parameters of the module itself. However, the phase differences among multiple ports cannot be simply represented by the differences between the output power of the module and the ideally combined power, because the impedances of all ports except measuring ports should be perfectly matched. The proposed method uses a parameter that compensates for the impedance mismatches generated at the other ports to achieve precise measurement of the phase differences among multiple ports. The measurement results using the passive component with three ports reveal that the mean errors of the proposed method are 1.26% and 2.15° in the amplitude and phase, respectively, when compared with measurements using the vector network analyzer. The standard deviations of the errors show 1.68% and 1.67° in the amplitude and phase, respectively. [ABSTRACT FROM AUTHOR]

This paper presents two single-pole, double-throw (SPDT) mm-wave switches for Ka-band phased-array transceivers, fabricated with a 65-nm complementary metal oxide semiconductor (CMOS) process. One switch employs cross-biasing (CB) control with a single supply, while the other uses dual-supply biasing (DSB) control with positive and negative voltages. Negative voltages were generated internally, using a ring oscillator and a charge pump. Identical gate and body floated N-type metal oxide semiconductor field effect transistors (N-MOSFETs) in a triple well were used as the switch core transistors. Inductors were used to improve the isolation between the transmitter (TX) and receiver (RX), as well as insertion loss, by canceling the parasitic capacitance of the switch core transistors at resonance. The size of the proposed radio frequency (RF) switch is 260 μm × 230 μm, excluding all pads. The minimum insertion losses of the CB and DSB switches were 2.1 dB at 28 GHz and 1.93 dB at 24 GHz, respectively. Between 25 GHz and 34 GHz, the insertion losses were less than 2.3 dB and 2.5 dB, the return losses were less than 16.7 dB and 17.3 dB, and the isolation was over 18.4 dB and 15.3 dB, respectively. The third order input intercept points (IIP3) of the CB and DSB switches were 38.4 dBm and 39 dBm at 28 GHz, respectively. [ABSTRACT FROM AUTHOR]

We report a high-performance plasmonic terahertz (THz) detector based on an antenna-coupled asymmetric FET by using the 65-nm CMOS technology. By designing an asymmetric FET on a self-aligned poly-Si gate structure, more enhanced channel charge asymmetry between the source and the drain has been obtained in comparison with the nonself-aligned metal gate structure of our previous paper. In addition, using a vertically integrated patch antenna, which is designed for a 0.2-THz resonance frequency, we demonstrated the highly enhanced detection performance with a responsivity of 1.5 kV/W and a noise-equivalent power of 15 pW/Hz0.5 at 0.2 THz. [ABSTRACT FROM AUTHOR]

ABSTRACT The miniaturized radar sensor for detecting short distances is realized using a six-port network. The six-port network of the radar sensor consists of passive components and RF power detectors. The power detector obtains a highly accurate DC voltage because DC offsets are cancelled using a dummy structure in the detector. The maximum error of a distance measurement to 3 m is approximately 2% for a single target. Using traveling wave antennas, the distances to two targets with different directions are measured with 6.7% maximum detection error to 1 m. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2634-2637, 2014 [ABSTRACT FROM AUTHOR]

A CMOS detector with a concurrent mode for high-quality images in the sub-terahertz region has been proposed. The detector improves output-signal coupling characteristics at the output node. A cross-coupling capacitor is added to isolate the DC bias between the drain and gate. The detector is designed to combine a 180° phase shift based on common source operation and an in-phase output signal based on the drain input. The circuit layout and phase shift occurring in the cross-coupled capacitor during phase coupling are verified using an EM simulation. The detector is fabricated using the TSMC 0.25-μm mixed-signal 1-poly 5-metal layer CMOS process, where the size, including the pad, is 1.13 mm × 0.74 mm. The detector IC comprises a folded dipole antenna, the proposed detector, a preamplifier, and a voltage buffer. Measurement results using a 200-GHz gyrotron source demonstrate that the proposed detector voltage responsivity is 14.13 MV/W with a noise-equivalent power of 34.42 pW/√Hz. The high detection performance helps resolve the 2-mm line width. The proposed detector exhibits a signal-to-noise ratio of 49 dB with regard to the THz imaging performance, which is 9 dB higher than that of the previous CMOS detector core circuits with gate-drain capacitors. [ABSTRACT FROM AUTHOR]

Vital signal detection using multiple radars is proposed to reduce the signal degradation from a subject's body movement. The phase variation in the transceiving signals of continuous-wave radar due to respiration and heartbeat is generated by the body surface movement of the organs monitored in the line-of-sight (LOS) of the radar. The body movement signals obtained by two adjacent radars can be assumed to be the same over a certain distance. However, the vital signals are different in each radar, and each radar has a different LOS because of the asymmetric movement of lungs and heart. The proposed method uses two adjacent radars with different LOS to obtain correlated signals that reinforce the difference in the asymmetrical movement of the organs. The correlated signals can improve the signal-to-noise ratio in vital signal detection because of a reduction in the body movement effect. Two radars at different frequencies in the 5.8 GHz band are implemented to reduce direct signal coupling. Measurement results using the radars arranged at angles of 30°, 45°, and 60° showed that the proposed method can detect the vital signals with a mean accuracy of 97.8% for the subject moving at a maximum velocity of 53.4 mm/s. [ABSTRACT FROM AUTHOR]

A detrending technique is proposed for continuous-wave (CW) radar to remove the effects of direct current (DC) offset, including DC drift, which is a very slow noise that appears near DC. DC drift is mainly caused by unwanted vibrations (generated by the radar itself, target objects, or surroundings) or characteristic changes in components in the radar owing to internal heating. It reduces the accuracy of the circle fitting method required for I/Q imbalance calibration and DC offset removal. The proposed technique effectively removes DC drift from the time-domain waveform of the baseband signals obtained for a certain time using polynomial fitting. The accuracy improvement in the circle fitting by the proposed technique using a 5.8 GHz CW radar decreases the error in the displacement measurement and increases the signal-to-noise ratio (SNR) in vital signal detection. The measurement results using a 5.8 GHz radar show that the proposed technique using a fifth-order polynomial fitting decreased the displacement error from 1.34 mm to 0.62 mm on average when the target was at a distance of 1 m. For a subject at a distance of 0.8 m, the measured SNR improved by 7.2 dB for respiration and 6.6 dB for heartbeat. [ABSTRACT FROM AUTHOR]

We demonstrate the performance enhancement of field-effect transistor (FET)-based plasmonic terahertz (THz) detector with monolithic integrated antenna in low-impedance regime and report the experimental results of Si MOSFET impedance in THz regime using 0.2-THz measurement system. By designing FET with low-impedance ranges (<1 k $\Omega )$ and integrating antennas with impedances of 50 and $100~\Omega $ , we found that our low-impedance MOSFETs have the input impedance criterion of $50~\Omega $ at 0.2 THz and the MOSFETs with thinner gate oxide show the highly enhanced plasmonic photoresponses at 50- $\Omega $ antenna by 325 times from the result of the detector without antenna. [ABSTRACT FROM AUTHOR]

This letter proposes a method for measuring the amplitude and phase differences between two RF signals at the same frequency. It uses power combining components and a signal power detector. The differences are calculated from the proposed equations using the power measurements of each signal and the combined signal. The method is demonstrated at 10 MHz and 5 GHz frequencies. The maximum errors in the GHz-band are 3.6% in the amplitude and 4.5^\circ in the phase, and the standard deviations in the measurement are 1.94% in the amplitude and 2.16^\circ in the phase. [ABSTRACT FROM PUBLISHER]

The aim of this paper is to find the optimal mother wavelet function and wavelet decomposition level when denoising the Doppler cardiogram (DCG), the heart signal obtained by the Doppler radar sensor system. To select the best suited mother wavelet function and wavelet decomposition level, this paper presents the quantitative analysis results. Both the optimal mother wavelet and decomposition level are selected by evaluating signal-to-noise-ratio (SNR) efficiency of the denoised signals obtained by using the wavelet thresholding method. A total of 115 potential functions from six wavelet families were examined for the selection of the optimal mother wavelet function and 10 levels (1 to 10) were evaluated for the choice of the best decomposition level. According to the experimental results, the most efficient selections of the mother wavelet function are "db9" and "sym9" from Daubechies and Symlets families, and the most suitable decomposition level for the used signal is seven. As the evaluation criterion in this study rates the efficiency of the denoising process, it was found that a mother wavelet function longer than 22 is excessive. The experiment also revealed that the decomposition level can be predictable based on the frequency features of the DCG signal. The proposed selection of the mother wavelet function and the decomposition level could reduce noise effectively so as to improve the quality of the DCG signal in information field. [ABSTRACT FROM AUTHOR]

A voltage-controlled oscillator (VCO) is a key component to generate high-speed clock of mixed-mode circuits and local oscillation signals of the frequency conversion in wired and wireless application systems. In particular, the recent evolution of new high-speed wireless systems in the millimeter-wave frequency band calls for the implementation of the VCO with high oscillation frequency and low close-in phase noise. The effect of the flicker noise on the phase noise of the VCO should be minimized because the flicker noise dramatically increases as the deep-submicron complementary metal-oxide-semiconductor (CMOS) process is scaled down, and the flicker corner frequency also increases, up to several MHz, in the up-to-date CMOS process. The flicker noise induced by the current source is a major factor affecting the phase noise of the VCO. Switched-biasing techniques have been proposed to minimize the effect of the flicker noise at the output of the VCO with biasing AC-coupled signals at the current source of the VCO. Reviewing the advantages and disadvantages reported in the previous studies, it is analyzed which topology to implement the switched-biasing technique is advantageous for improving the performance of the CMOS VCOs. [ABSTRACT FROM AUTHOR]

In this paper, we propose a Doppler spectrum-based passenger detection scheme for a CW (Continuous Wave) radar sensor in vehicle applications. First, we design two new features, referred to as an 'extended degree of scattering points' and a 'different degree of scattering points' to represent the characteristics of the non-rigid motion of a moving human in a vehicle. We also design one newly defined feature referred to as the 'presence of vital signs', which is related to extracting the Doppler frequency of chest movements due to breathing. Additionally, we use a BDT (Binary Decision Tree) for machine learning during the training and test steps with these three extracted features. We used a 2.45 GHz CW radar front-end module with a single receive antenna and a real-time data acquisition module. Moreover, we built a test-bed with a structure similar to that of an actual vehicle interior. With the test-bed, we measured radar signals in various scenarios. We then repeatedly assessed the classification accuracy and classification error rate using the proposed algorithm with the BDT. We found an average classification accuracy rate of 98.6% for a human with or without motion. [ABSTRACT FROM AUTHOR]

A frequency-shift keying (FSK) radar in the 2.45-GHz band is proposed for highly accurate vital-signs detection. The measurement accuracy of the proposed detector for the heartbeat is increased by using the cross-correlation between the phase differences of signals at two frequencies used by the FSK radar, which alternately transmits and receives the signals with different frequencies. Two frequencies—2.45 and 2.5 GHz—are effectively discriminated by using the envelope detection with the frequency control signal of the signal generator in the output waveform of the FSK radar. The phase difference between transmitted and received signals at each frequency is determined after calibrating the I/Q imbalance and direct-current offset using a data-based imbalance compensation algorithm, the Gram–Schmidt procedure, and the Pratt method. The absolute-distance measurement results for a human being show that the vital signs obtained at each frequency using the proposed FSK radar have a cross-correlation. The heartbeat detection results for the proposed FSK radar at a distance of < 2.4 m indicate a reduction in the error rate and an increase in the signal-to-noise ratio compared with those obtained using a single operating frequency. [ABSTRACT FROM AUTHOR]

Highlights from the article: "The radar sensor operating in the 915 MHz industrial, scientific, and medical ratio band can have high accuracy for detecting vital-sign information due to high penetration and low signal loss in the human body". "The radar sensor operating in the 915 MHz industrial, scientific, and medical radio band can have high accuracy for detecting vital-sign information due to high penetration and low signal loss in the human body". 1 Park J.-H., Jeong Y.-J., Lee G.-E., Oh J.-T., Yang J.-R. 915-MHz Continuous-Wave Doppler Radar Sensor for Detection of Vital Signs.

A miniaturized continuous-wave Doppler radar sensor operating at 915 MHz to remotely detect both respiration and heart rate (beats per minute) is presented. The proposed radar sensor comprises a front-end module including an implemented complementary metal-oxide semiconductor low-noise amplifier (LNA) and fractal-slot patch antennas, whose area was reduced by 15.2%. The two-stage inverter-based LNA was designed with an interstage capacitor and a feedback resistor to acquire ultrawide bandwidth. Two operating frequencies, 915 MHz and 2.45 GHz, were analyzed with regard to path loss for efficient operation because frequency affects detection sensitivity, reflected signal power from the human body, and measurement distance in a far-field condition. Path-loss calculation based on the simplified layer model indicates that the reflected power of the 915 MHz radar could be higher than that of the 2.45 GHz radar. The implemented radar front-end module excluding the LNA occupies 35 × 55 mm2. Vital signs were obtained via a fast Fourier transform and digital filtering using raw signals. In an experiment with six subjects, the respiration and heart rate obtained at 0.8 m using the proposed radar sensor exhibited mean accuracies of 99.4% and 97.6% with respect to commercialized reference sensors, respectively. [ABSTRACT FROM AUTHOR]

An accurate method for detecting vital signs obtained from a Doppler radar sensor is proposed. A Doppler radar sensor can remotely obtain vital signs such as heartbeat and respiration rate, but the vital signs obtained by using the sensor do not show clear peaks like in electrocardiography (ECG) because of the operating characteristics of the radar. The proposed peak detection algorithm extracts the vital signs from the raw data. The algorithm shows the mean accuracy of 96.78% compared to the peak count from the reference ECG sensor and a processing time approximately two times faster than the gradient-based algorithm. To verify whether heart rate variability (HRV) analysis similar to that with an ECG sensor is possible for a radar sensor when applying the proposed method, the continuous parameter variations of the HRV in the time domain are analyzed using data processed with the proposed peak detection algorithm. Experimental results with six subjects show that the proposed method can obtain the heart rate with high accuracy but cannot obtain the information for an HRV analysis because the proposed method cannot overcome the characteristics of the radar sensor itself. [ABSTRACT FROM AUTHOR]

An analytic method for a complementary metal-oxide-semiconductor (CMOS) terahertz plasmon detector operating in the subthreshold region is presented using the equivalent circuit model. With respect to design optimization of the detector, the signal transmission from the antenna port to the output of the detector is described by using the proposed circuit model, which does not include a complicated physical operating principle and mathematical expressions. Characteristics from the antenna port to the input gate node of the detector are analyzed through the superposition method by using the characteristic impedance of transmission lines. The superposition method shows that the effect of interconnection lines at the input is simplified with the optimum bias point. The characteristics of the plasmon detection are expressed by using small-signal analysis of the single transistor at the sub-threshold operation. The results of the small-signal analysis show that the unity gain preamplifier located between the detector core and the main amplifier can improve the detection performances such as the voltage responsivity and the noise equivalent power. The measurement results using the fabricated CMOS plasmon detector at 200 GHz suggest that the unity gain preamplifier improves the detector performances, which are the same results as we received from the proposed analytic method. [ABSTRACT FROM AUTHOR]

A quasi-circulator is proposed by using an asymmetric coupler with high isolation between the transmitting (Tx) and receiving (Rx) ports. The proposed quasi-circulator consists of quarter-wave transmission lines, which have unbalanced characteristic impedances and the terminated port, which is purposely unmatched with the reference impedance in the coupler. The port compensates for the asymmetric impedances of the coupler using the proposed design parameter. Because of its asymmetric structure and the usage of the unmatched port, the proposed circulator can be accurately designed to have high Tx–Rx isolation without increasing the signal losses in the Tx and Rx paths at the operating frequency. The proposed quasi-circulators show isolation improvements of 9.07 dB at 2.45 GHz and 7.95 dB at 24.125 GHz compared with conventional circulators using the symmetric couplers. The characteristic improvement of the proposed quasi-circulator was demonstrated by the increase of the detectable range of the 2.45 GHz Doppler radar sensor with the quasi-circulator. [ABSTRACT FROM AUTHOR]

In this article, a highly efficient power module is presented with two class-E power amplifiers and an adaptive power combiner for transmitting output powers >100 W at 6.78 MHz in a wireless power transfer system. The losses caused by the combiners and interstage matching circuits or mismatching between the amplifier, and the combiners can significantly reduce the overall efficiency of the power module. To achieve an efficient combination of the output amplifier signals, the adaptive power combiner is proposed based on the consideration of the optimum load impedance characteristics of the power amplifiers. The input impedance of the combiner is designed using series capacitors and resistors between the two input ports of the combiner and the two output signals of the class-E amplifiers at the optimum load condition. The output performances of the proposed module can decrease based on the component mismatch between the two power amplifiers. The proposed power module was implemented on an FR4 PCB, with a 15 mm metal heat sink, and demonstrated an output power of 123.3 W, a power-added efficiency of 85.7%, and a power gain of 25.6 dB at 6.78 MHz. The second harmonic suppression of the module was 37 dBc. [ABSTRACT FROM AUTHOR]