Local Oscillator Signal Research Articles

A Battery-Less Portable ECG Monitoring System With Wired Audio Transmission.

This paper proposes a batteryless electrocardiogram (ECG) monitoring chip and intelligent system with wired audio transmission, which can be applied to long-term and real-time ECG monitoring. The ECG signal is modulated and amplified in the front-end chip and then is transmitted through the microphone channel of the 3.5-mm headphone cable. The sinusoidal signals from the left and right channels are converted into a dc supply and a precise local oscillator signal in the front-end chip, respectively. The proposed system samples the signal through the high-precision audio analog-to-digital converter in smart devices and processes it through the internal software. Therefore, no external battery, local oscillator, and complicate modules are required in this system. A chopper/amplitude modulation (AM) reused mixer amplifier is proposed, which combines chopping with AM and reuses the local oscillator signal. The closed-loop gain of the proposed amplifier varies between 20 and 47 dB and can be automatically adjusted according to the amplitude of the output signal. The proposed chip was implemented in a standard 0.18-μm CMOS process and occupies 1.07 × 0.95 mm2 of core area. The power management module outputs a 1.5-V dc voltage to power the system. When connected with the headphone cable load, the chip consumes a total power of 156 μW. The proposed monitoring system has been verified by the audio device and MATLAB in the PC. The test results show that the input reference noise of the demodulated signal is 2.12 μVrms (0.1-200Hz) and the total harmonic distortion is 0.56%@3 mV input.

Reconfigurable microwave photonic frequency upconverter with local oscillator doubling or local oscillator quadrupling

A reconfigurable microwave photonic frequency upconverter with local oscillator (LO) doubling or LO quadrupling is proposed based on two cascaded dual-parallel Mach–Zehnder modulators (DPMZMs) and a fiber Bragg grating (FBG) with a wide bandwidth (0.4 nm). The first DPMZM is used to generate the ±1st-order or ±2nd-order sidebands of the LO signal. The FBG is inserted to separate the positive and negative sidebands. Only the transmitted LO sideband is sent to the second DPMZM, and the carrier-suppressed single-sideband (CS-SSB) modulation of the intermediate frequency (IF) signal is realized by using an electrical 90 deg hybrid coupler. The reflected LO sideband via FBG and the −1st-order IF sideband are combined. Then, the upconverted signal with the frequency of 2ωLO + ωIF or 4ωLO + ωIF can be generated by a photodetector. The experimental results show that the spur suppression ratios of the upconverter with LO doubling and quadrupling are 21.3 and 11.3 dB, respectively. The proposed approach greatly reduces the frequency requirement of the LO signal. The purity of electrical spectrum is largely improved in both the LO doubling and LO quadrupling upconversion benefiting from the CS-SSB modulation. Furthermore, these two upconversion modes can be easily switched by tuning the DC biases of the first DPMZM.

Photonic radiofrequency receiver utilizing a phase modulator and a tunable single sideband optoelectronic oscillator

AbstractA photonic radiofrequency (RF) receiver utilizing a phase modulator (PM) and a tunable single sideband (SSB) optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. In this scheme, the RF signal to be detected is modulated on the PM in one optical path, while a local oscillation (LO) signal is optically generated by the SSB OEO in the other optical path. After combining two paths of optical signals via an optical coupler, an immediate frequency (IF) signal is obtained by photonic RF downconversion in a photodetector (PD). Through scanning the LO signal and monitoring the IF signal simultaneously, the input unknown RF signal can be detected. In the experiment, the RF tones with the operating frequency from 8.1 to 12.1 GHz are successfully detected. The minimum detectable RF power at 10.1 GHz is −84.6 dBm, and the spurious free dynamic range of the photonic RF receiver measured is about 73.8 dB/Hz2/3.

Mechanical Superheterodyne and Its Use for Low Frequency Vibrations Sensing

Mechanical micro and nano scale devices are being increasingly used for realizing signal processing and logic or computing functions, which until recently were traditionally performed by electronics. Extremely low-power consumption and robustness make mechanical micro structures attractive for implementation in autonomous distributed sensing systems. Heterodyning is one of the most important and indispensable signal processing techniques. In microelectromechanical heterodynes, the frequency mixing is commonly achieved using nonlinear forces, which often limits scalability and the operational range of the device and may lead to undesired dynamic behavior. In this paper, we introduce an approach allowing purely mechanical realization of the superheterodyne principle. The frequency mixing is based on the inertial coupling between two vibratory modes of the device. The architecture is distinguished by linearity of the mixing term with respect to the input inertial and the local oscillator signals. We demonstrate the mixing effect both theoretically and experimentally, using the devices fabricated from a silicon on insulator (SOI) wafer by deep reactive ion etching (DRIE). We show the applicability of the device as a mechanical low frequency vibration sensor. The substrate vibration frequencies down to 25 Hz were measured using a device with a fundamental mode frequency of 4700 Hz.

Measurement System for Millimeter-Wave Antennas With Distributed External Local Oscillators and Mixers

A measurement system for a millimeter-wave (mm-wave) antenna is presented here. The topologies of RF subsystems for antenna measurements are reviewed, and the optimum topology for a far-field antenna measurement range for mm-wave antennas is proposed. This topology minimizes the losses of both the Tx and local oscillator (LO) signal paths. In order to verify the proposed topology, a $W$ -band antenna measurement system for a fully anechoic chamber 10 ( $W$ ) m $\times \,\, 13$ ( $L$ ) m $\times \,\, 7.5$ ( $H$ ) m in size is designed and implemented. To provide the optimal LO input power, a test signal supply that compensates for the complicated losses in the LO signal path is also designed and implemented. The optimization procedure of the LO power is described. The performance of the $W$ -band antenna measurement system is evaluated by measuring the complex reflection coefficient and far-field gain of an electro-formed standard gain horn antenna. The measurement results are compared with intercomparison results between National Measurement Institutes. The results are shown to be within accepted uncertainty levels.

A 53–67 GHz Low-Noise Mixer-First Receiver Front-End in 65-nm CMOS

In this paper, we present a mixer-first receiver front-end suitable for millimeter wave (mm-wave) applications. The proposed architecture includes a modified single-balanced mixer core with an on-chip balun in order to provide a differential output from an injected single-ended local oscillator signal. The mm-wave active balun incorporates a cascode cross-coupled structure to achieve a high voltage gain with low amplitude and phase imbalance. The inter-stage inductors are utilized to increase the mixer conversion gain (CG). Moreover, by manipulating the transistor body effect in the transconductance stage, the CG and noise figure of the mixer are further improved. The mixer also achieves a high input return loss which makes it suitable for the mixer-first receivers. As a proof-of-concept, a 53–67 GHz mixer with a center intermediate-frequency of 20 GHz is designed and implemented in a 65-nm CMOS process. The mixer achieves a measured peak conversion gain of 12.1 dB and a 1-dB compression point of −5 dBm. Furthermore, the fabricated mixer achieves a minimum double-sideband (DSB) noise figure of 6.5 dB over its bandwidth. The whole chip consumes 11.5 mW from a 1-V supply and excluding the pads occupies 0.27 mm2 of silicon area.

A stable photonic generation scheme of triangular waveform with double frequency and variable power

ABSTRACTA microwave photonic generation scheme of triangular waveform using cascaded dual-drive Mach-Zehnder modulators (DDMZMs) and FBG is proposed. We show that a frequency-doubled and power-variable triangular waveform can be obtained. The double frequency can reduce the high-frequency requirement of the local oscillation signal (LO) source. The introduction of the second modulator can improve the stability of the scheme. The simulation results show that the power of the triangular is variable; the stability is optimized when the first modulation index is in 0 1; the similarity coefficient is greater than 0.998, which is 0.006 higher than one-stage-modulation scheme. Meanwhile, the similarity coefficient remains over 0.992 when the DC drifting difference value of and is in −90 60 mV, and it remains over 0.99 when the phase difference of the two LO sources varies from −10° to 10°. It verifies the tolerance of DC drifting and phase desynchrony of the system.

Microwave Downconversion by a Tunable Optoelectronic Oscillator Based on PS-FBG and Polarization-Multiplexed Dual loop

A novel photonic method for microwave downconversion by using a tunable optoelectronic oscillator (OEO) based on a phase-shifted fiber-Bragg grating (PS-FBG) and the polarization-multiplexed dual loop is proposed and investigated. By the virtue of the narrow notch bandwidth of the PS-FBG and the side-mode suppression of the optimized dual loop, the frequency tunable local oscillator (LO) signal with high spectral purity and low phase noise is generated by changing the frequency of the optical carrier from the laser source. The microwave downconversion is conducted directly by inputting the radio frequency (RF) signal into the OEO without any additional components. The experiment of the LO signal generation and the microwave downconversion is carried out. The frequency tunable LO signals from 2.5 to 7 GHz with the side-mode suppression ratio as high as 56 dB and the phase noise of −109 dBc/Hz at 10 kHz are generated successfully. By tuning the LO frequency generated by the proposed OEO, the RF signals with different frequencies from 3.5 to 8 GHz are converted to the same intermediate frequency band of 1 GHz. The spurious-free dynamic range of the downconversion system is measured to be 102.2 dB $\cdot $ Hz $^{2/3}$ . The downconversion performance for RF carrying 16 quadrature amplitude modulation signal is also analyzed.

Photonic-assisted wideband frequency downconverter with self-interference cancellation and image rejection.

A photonic-assisted wideband frequency downconverter with self-interference cancellation and image rejection for in-band full-duplex radio-over-fiber systems based on a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator is proposed. The upper dual-parallel Mach-Zehnder modulator (DP-MZM) of the DP-QPSK modulator is used to cancel the self-interference directly in the optical domain and generate two first-order optical sidebands of the desired received radio frequency (RF) signal. The lower DP-MZM generates two optical sidebands of the local oscillator signal with the optical carrier suppressed via properly biasing the modulator. The optical signals generated from the two DP-MZMs are combined, and then the upper and lower optical sidebands of the combined signal are separated by a wavelength division multiplexer (WDM). The two outputs from the WDM are detected by two photodetectors and then combined at a 90° hybrid coupler to achieve frequency downconversion and image rejection. A simulation is performed. A quadrature phase-shift keying (QPSK)-modulated RF signal is successfully downconverted to a 1-GHz intermediate frequency signal with self-interference and image frequency cancelled. The performance of the frequency downconverter is also evaluated.

Filter-free image-reject microwave photonic downconverter based on cascaded modulators.

As essential equipment of the receiver, a novel filter-free image-reject mixer based on a Mach-Zehnder modulator (MZM) and a polarization-division multiplexing Mach-Zehnder modulator (PDM-MZM) is proposed and experimentally demonstrated in this paper. The received radio frequency signal is applied to the MZM, and quadrature local oscillator signals are sent to the PDM-MZM, which includes two submodulators in parallel. After a polarization controller and a polarization beam splitter, quadrature intermediate frequency (IF) signals are obtained by two photodetectors. Image rejection is implemented by combining quadrature IF signals via an electrical 90° hybrid coupler. The scheme uses no filter, so the working frequency can be widely tuned and effective spectrum utilization is achieved. Experimental results verify that image rejection ratios can reach 50dB. Moreover, the variation of the conversion gain is lower than 2dB.

Practical Security Analysis of Self-Referenced CV-QKD System in the Presence of Polarization Aberration

How to remove local oscillator (LO) side channel attacks has been a notoriously hard problem in continuous-variable quantum key distribution (CV-QKD). In the self-referenced CV-QKD schemes, the LO signal is locally generated at the receiver by an independent laser so that it is not co-transmitted with the quantum signal. This simple solution removes all LO side channels. However it also introduces some other practical vulnerabilities. Especially the polarization states of the quantum signal and LO signal may not be identical across the detector because of the presence of the polarization aberrations. Thus, the detection efficiency which is arguably the most critical experiment parameter of the practical implementation will be impaired. In this paper, we analyze the impact of polarization aberrations on the detection efficiency for CV-QKD and propose a self-referenced CV-QKD scheme in the presence of polarization aberrations by using an off-axis optical system. In the proposed scheme, the polarization states of the quantum signal would change with the off-axis optical system, thus impairing the heterodyne efficiency. Our security analysis shows a gap between the theory and practice of CV-QKD.

Wideband photonic microwave channelization and image-reject down-conversion

A wideband photonic microwave channelization and image-reject down-conversion system is proposed and experimentally demonstrated. The broadband radio frequency (RF) and electrical local oscillator (LO) signals are applied to Mach–Zehnder modulators (MZMs) and be multiplexed for channelized reference. By employing DPMZMs, different optical frequency shifting LO signals for channelization are generated. Due to the frequency difference between the modulated RF signals and frequency shifted LO signals, multichannel intermediate frequency (IF) signals can be easily separated by the followed photonic I/Q receiver. Experimental results show that the RF signal with a bandwidth of 3 GHz could be down-converted into six IF signals with the same center frequency of 750 MHz and the same bandwidth of 500 MHz. The measured spurious free dynamic range (SFDR) is 101 dB•Hz 2∕3, the passband fluctuation is less than 0.5 dB; the channel isolation is over 22 dB, and the image-rejection is over 22 dB. A QPSK vector signals with 50 Msym/s and 16.5–19.5 GHz operating frequency is successfully demonstrated using the proposed scheme, and good EVMs and constellation diagrams are obtained. The proposed photonic channelization and image-reject down-conversion system may have potential applications in the RF frontends of future systems such as broadband integrated satellite communication and multi-service wireless networks.

A Fully Integrated 150-GHz Transceiver Front-End in 65-nm CMOS

A fully integrated D-band transceiver front-end with on-chip frequency synthesizer is implemented in 65-nm CMOS. The transceiver front-end adopts the dual-conversion sliding-IF heterodyne architecture to relax the design difficulty of the local oscillation (LO) signal generator. The D-band signal is first down-converted via a 100-GHz LO signal and IQ down-converted via a 50-GHz quadrature LO signal in the receiver (RX). While in the transmitter, the modulated signal is generated at 50 GHz and up-converted via a 100-GHz LO signal. The measured transmitter output power is 2.1 dBm at 150 GHz, with >11 GHz 3-dB bandwidth. The measured results also show the cascaded gain of the RX can be programmed from 57.4 dB to 45.6 dB with 3-dB bandwidth of 9.6 GHz to >20 GHz.

Microwave-Photonics Frequency Up-Converter for Telecom and Measurement Equipment

An ultra-wideband tunable frequency converter scheme for microwave and millimeter-wave signal generation based on optical recirculating loop and microwave-photonics technique, is proposed and demonstrated. The scheme consists of standard, commercially available elements such as dual parallel Mach-Zehnder modulator, optical filter, wideband photodiode and does not require ultra-broadband RF components. A recirculating loop acts as an optical frequency comb generator and allows obtaining multiple local oscillator signals at frequencies that significantly higher than the RF reference used. Up-converted signals of frequencies in mm-wave band are demonstrated experimentally with spectra free of spurious products. The converter proposed could be used as an alternative solution to microwave mixers in telecom and measurement equipment.

Cascaded modulator topology for frequency conversion in antenna remoting applications.

A new cascaded modulator structure that has the ability to realize high conversion efficiency microwave frequency downconversion, while at the same time able to overcome two fundamental limitations in the dual-parallel modulator approach, is presented. It is based on utilizing the polarization-dependent modulation efficiency property in LiNbO3 electro-optic modulators. The new structure allows the modulators for the RF signal and local oscillator (LO) modulation to be placed in different locations suitable for antenna remoting applications, and it has infinite isolation between the LO and RF signal ports. We present experimental results demonstrating that the proposed structure can be used to realize high conversion efficiency frequency downconversion over wide RF and intermediate frequency (IF) signal frequency ranges as the reported dual-parallel-modulator-based microwave photonic frequency downconverter. Very high isolation of more than 70dB between the LO and RF signal ports is also demonstrated.

A compact 0.045–2.3 GHz frequency synthesizer with a wide tuning range low phase noise VCO for software defined radios

A compact 0.045–2.3 GHz wideband fractional-N frequency synthesizer (FS) for software defined radios (SDR) applications is presented in this paper. Based on a single phase locked loop (PLL) that employs one integrated inductor-capacitor voltage controlled oscillator (VCO), the proposed FS can provide a wide operating frequency range. The VCO adopts an optimized circular inductor to mitigate the phase noise degradation caused by the high VCO gain. The in-band phase noise is optimized by employing current mode logic dividers and true single phase clock dividers. The PLL provides the differential outputs ranging from 2.3 to 4.6 GHz and the 0.045–2.3 GHz quadrature local oscillator signals are generated by the following divider chain. The proposed FS is implemented in TSMC 180 nm RFCMOS process and provides a phase noise performance less than − 116 dBc/Hz at 1 MHz offset. The maximum power consumption is 54 mW. The die size including pads and I/O is 1.92 mm2 with an active core area of 1.13 mm2. This proposed circuit has the great potential for SDR applications.

Photonic approach for simultaneous measurements of Doppler-frequency-shift and angle-of-arrival of microwave signals.

A photonic method used to simultaneously measure the Doppler-frequency-shift (DFS) and angle-of-arrival (AOA) of microwave signals is proposed and experimentally demonstrated. At the remote antenna unit (RAU), the local oscillator (LO) signal and two echo signals are applied to a phase modulator (PM) and a polarization-division-multiplexed Mach-Zehnder modulator (PDM-MZM), respectively. After transmission over a fiber link, the DFS and AOA parameters can be obtained by processing the two low-frequency electrical signals at the central office (CO). Experimental results show that the DFS between ± 100-kHz with < ± 5 × 10-3-Hz error and the AOA from 1.82° to 90° with <0.85° error at 10 GHz are obtained over a 10-km single mode fiber (SMF) transmission. Moreover, the DFS direction can also be distinguished by comparing the phase difference of two electrical signals.

Tunable OEO-based photonic RF receiver with image frequency rejection.

A tunable optoelectronic oscillator (OEO)-based photonic radio frequency (RF) heterodyne receiver with the capability of image frequency rejection is proposed and experimentally demonstrated. The OEO incorporating a dual-electrode Mach-Zehnder modulator (DEMZM) operates as a high quality local oscillator (LO) and a broadband mixer simultaneously, with one electrode port of the DEMZM used for the feedback of the generated LO signal and the other port for receiving external RF signals. Two channels of immediate frequency (IF) signals can be achieved in optical domain by beating the +1-order sideband of LO with the +1-order sideband of input RFs and beating the -1-order sideband of LO with the -1-order sideband of input RFs correspondingly. Through setting the bias angle of the DEMZM at π/4 or 5π/4 and quadrature combining of the two channels of the IF signal, the combined IF signal down-converted from the target RF signal gets enhanced due to the in-phase sum of two channels, while the combined IF signal down-converted from the image frequency can be rejected due to out-of-phase sum of two channels. In the experiment, the input RF signals with operating frequency range from 8.85 to 14.85GHz are successfully received with the image rejection ratio reaching 42.6dB, and the spurious free dynamic range of the system is better than 94.8 dB Hz2/3.

Design Considerations for Image-Rejection Enhancement of Quadrature Mixers

In this letter, the influences of local oscillator (LO) reflections of the in-phase (I) and quadrature-phase (Q) mixers and limited isolations between the I/Q LO ports on the image-rejection ratio (IRR) performances of quadrature mixers are investigated and analyzed for the first time. The analysis reveals that, in addition to generating well-balanced quadrature LO signals, a good LO impedance matching and/or high electrical isolation between the LO ports of the I and Q mixers are required to obtain a high IRR over a wide bandwidth. To verify the analysis, a quadrature mixer with carefully designed wideband LC-ladder matching networks for the I/Q LO ports is implemented in a 65-nm CMOS technology. Under 1-V supply voltage and 3-dBm LO power, the proposed quadrature mixer exhibits 3.3±1.5 dB conversion gain and better than 30-dBc IRR across the 20–25-GHz band.

Live electrooptic imaging with a low-coherence optical LO signal source for suppression of interference noises.

Reported in this paper is the first application, to our knowledge, of a low-coherence optical local oscillator signal source to the live electrooptic imaging (LEI) scheme, where high frequency electric field (EF) distributions are visualized in real time. A fiber-optic super luminescent diode (SLD) in conjunction with a LiNbO3 Mach-Zehnder modulator (MZM) was found to work well for the real-time imaging of gigahertz-range EF distributions with high suppression of interference pattern image noises (IPINs), which have long been a problem to be solved. While the SLD-based LEI system works up to the MZM bandwidth (10GHz), IPINs caused by microscopic defects in an electrooptic sensor appear, suggesting a limitation given by the SLD coherence length.