Local Oscillator Signal Research Articles

Reconfigurable Photonic Generation of Binary Modulated Microwave Signals

A novel photonic scheme of binary modulated microwave signals generation based on a dual-polarization quadrature phase-shift keying (DP-QPSK) modulator is proposed and experimentally demonstrated. The scheme is highly reconfigurable, amplitude keying signal (ASK), phase-shift keying signal (PSK) or frequency-shift keying (FSK) signal can be generated by appropriately setting the amplitude of the binary coding signal. The coding signal and local oscillator (LO) signals are independent with each other, binary modulated microwave signals can be generated with arbitrary coding rate and carrier frequency. The frequency deviation of the FSK signal can also be adjusted flexibly. No filter is used in the scheme and the tuning range is large. A proof-of-concept experiment is carried out to verify the feasibility of the proposed system. A 1-Gbps 8-GHz microwave ASK signal, a 0.5-Gbps 6-GHz microwave PSK signal, and a 0.5-Gbps 8/12-GHz microwave FSK signal are g[enerated in the experiment.

A Reconfigurable Passive Mixer-Based Sub-GHz Receiver Front-End for Fast Spectrum Sensing Functionality

A reconfigurable parallel mixing subharmonic mixer (SHM)-based time-interleaved RF channelizer is proposed for fast spectrum sensing. The reconfigurable mixer operates as a double-balanced mixer (DBM), a double-balanced mixer with harmonic rejection (DBM&HR), and an SHM. In contrast to conventional spectrum sensing receivers to detect RF frequency bands by sweeping local oscillator (LO) frequencies, the proposed receiver scans multiple frequency bands quickly through mode change of the reconfigurable mixer. The LO generation circuit employs a voltage subtractor-based phase adder and provides highly accurate 25% duty-cycle octet-phase LO signals. The front-end implements a high LO harmonic rejection ratio (HRR) in order to avoid signal corruption by LO harmonic mixing during spectrum sensing. In experiments, the proposed receiver achieves <; 40.3 dB conversion gain, <; 6.6 dB noise figure (NF), > -35.8 dBm in-band input-referred third-order intercept point (IIP3), > -22.3 dBm out-of-band IIP3, and an average 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> LO HRR of 43 dB over 300-800 MHz in DBM&HR mode. Over 600-1200 MHz in SHM mode, it shows >31.8 dB conversion gain, <; 10.4 dB NF, > -30.9 dBm in-band IIP3, and > -20.1 dBm out-of-band IIP3. The switching time between DBH&HR and SHM modes is approximately 135 ns. The power dissipation is 24.7 mW from a 1.2 V supply voltage.

Optical Self-Interference Cancellation With Frequency Down-Conversion Based on Cascade Modulator

A novel approach to simultaneous radiofrequency self-interference cancellation (SIC) and frequency down-conversion in a unified system is proposed and demonstrated experimentally based on cascade Mach-Zehnder modulators (MZM). The local oscillator signal is injected into the MZM1, whereas the received RF signal and the reference signal are fed into MZM2 and MZM3. After photoelectrical conversion by a balanced photodetector, the desired intermediate frequency signal with SIC is obtained. The cancellation depth for the single frequency SIC with frequency down-conversion is around 38 dB, and that for a wideband signal is around 19 dB. No electrical delay and attenuation are used in the proposed system, so it can potentially reach a wider frequency band and a higher cancellation depth.

Switchable and filter‐free photonic microwave single‐sideband frequency converter

AbstractA switchable and filter‐free photonic microwave single‐sideband frequency converter based on a dual‐parallel dual‐drive Mach‐Zehnder modulator is proposed and experimentally demonstrated. Two first‐order carrier‐suppression single sidebands for input signal and local oscillator signal are achieved by adjusting the DC bias voltages of the modulator. The frequency upconversion and downconversion can be switched by adjusting one DC bias voltage of the modulator. Thanks to the carrier‐suppression single‐sideband modulation without using any filter, the frequency converter has a large operating bandwidth but no power fading caused by chromatic dispersion, and the mixing spurs can be effectively suppressed. Experimental results show that the frequency converted signal is pure over a wide frequency range, and the sideband suppression ratio of desired signal is over 20 dB. The spur free dynamic range achieves 108.3 dB Hz2/3.

Microwave Photonic Wideband Distributed Coherent Aperture Radar With High Robustness to Time Synchronization Error

In this article, we firstly analyze the specific effect of time and phase synchronization errors on the coherent gain of microwave photonic wideband distributed coherent aperture radar (DCAR), and further propose a robust design based on bandwidth segmentation. In our design, the intermediate-frequency narrowband linear frequency modulated waveform (LFMW) sub-pulses are mixed with the stepped-frequency local oscillator signals at the transmitter, generating the stepped-frequency LFMW. To ensure the waveform purity, a photonics-based single-sideband up-converter is proposed as the mixer. At the receiver side, the echo wave is processed by a photonics-based down-converter combined with the matched-filtering processing. The relatively low-resolution range profiles with low coherent gain loss can be achieved by the narrowband sub-pulses, and the high-resolution range profile with low coherent gain loss can be synthesized from these low-resolution range profiles. The coherent gain of the proposed system is less sensitive to time synchronization error comparing to the system where the wideband LFMW is transmitted. Higher level of robustness also enables easier implementation of such system. To show the effectiveness of our design, we conduct simulations and further establish an X-band (8–12 GHz) microwave photonic system with two transmitters and one receiver. The coherent gain under different time synchronization errors are measured. Both the simulation and experimental results confirm that the proposed system achieves a higher robustness to time synchronization error. For instance, to keep the coherent gain loss less than 0.3 dB, the required time synchronization accuracy can be relaxed from 35 ps to 127 ps.

Photonic Generation of Frequency-Doubled Triangular-Shaped Waveforms Based on a PM-MZM Modulator

We propose and experimentally demonstrate a simple and stable photonic approach of frequencydoubled triangular-shaped waveform generation. It mainly consists of an integrated polarizationmultiplexing Mach–Zehnder modulator (PM-MZM) and a balance photoelectric detector (BPD). Two PM-MZM sub-modulators work at the maximum transmission point. By properly setting the amplitude of the local oscillator (LO) signal, frequency-doubled triangular-shaped waveforms can be generated. We analyze the operational principle by theory and experiment. Experimental results show that, when the frequency of LO signal is set to 3, 4, and 5 GHz respectively, triangular-shaped waveform signals with different repetition rates of 6, 8, and 10 GHz are generated, which agree well with the theoretical prediction. The structure of this system is simple and compact. In addition, the system has high-frequency tunability and operating bandwidth due the absence of optical filters.

Reconfigurable photonic binary phase-coded microwave signal generator with fundamental/subharmonic carrier frequency.

A reconfigurable photonic binary phase-coded microwave signal generator with fundamental/subharmonic carrier frequency is proposed and experimentally investigated based on a dual-electrode dual parallel Mach-Zehnder modulator (DE-DPMZM). The local oscillator (LO) signal and coding signal are intensity modulated and phase modulated, respectively, on the two arms of the DE-DPMZM. The bias voltage of the intensity modulator is set to the quadrature or maximum working points to produce fundamental or subharmonic frequency, respectively. By precisely adjusting the amplitude of the LO signal and the bias voltage of the parent modulator, the light carriers of both arms of the DE-DPMZM can be eliminated. After detection, binary phase-coded microwave signal with frequency equal to or twice the frequency of the LO signal can be generated. The proposed system has a simple structure, high reconfigurability, and good frequency tunability due to its avoidance of using optical filters. In the experiment, phase-coded microwave waveforms at 6 GHz and 11 GHz are generated by using 6 GHz and 11 GHz LO signals or 3 GHz and 5.5 GHz LO signals, respectively. Meanwhile, the performance is evaluated in terms of phase recovery accuracy and pulse compression capability. The experimental results show that the proposed generator has high peak-to-sidelobe ratio, which has practical significance for radar detection of weak targets.

Photonics-Assisted Frequency Up/Down Conversion With Tunable OEO and Phase Shift

A novel photonics-assisted method for frequency up/down-conversion based on an integrated dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM) with tunable optoelectronic oscillator (OEO) and phase shift is presented. The local oscillator (LO) signal with high spectral purity and low phase noise is generated by an OEO loop in one of the sub-DPMZMs. The frequency can be adjusted by an electrical bandpass filter (EBPF). The radio frequency (RF) signal is injected into another sub-DPMZM. The carrier-suppressed single-sideband (CS-SSB) modulation of both the LO and RF signals is achieved. The phase of the converted signal can be tuned by an integrated dual-channel phase modulator (DPM). Frequency up/down-conversion can be switched by tuning a single bias voltage of the DP-DPMZM. Multiple functions, including tunable LO signal generation, up/down-conversion and phase shifting, can be realized. Moreover, dispersion-induced power fading is well compensated due to CS-SSB modulation. In the experiments, the tunable LO signal from 5 to 18 GHz, with a sidemode suppression ratio as high as 46.1 dB and a phase noise level of −104.5 dBc/Hz @ 10 kHz at 10 GHz, is generated successfully. The spur suppression ratios of the up/down-converted signals are 32.6 dB and 35.6 dB, respectively. The up/down conversion performance for RF carrying 16 quadrature amplitude modulation (16-QAM) signal is also investigated. The phase shifting of dual-channel converted signals can be varied continuously and independently in the range of 0–360°, and the phase deviation is ±1.8°. The proposed compact link is characterized by function multiplexing and inherent dispersion compensation.

1–3-GHz Self-Aligned Open-Loop Local Quadrature Phase Generator With Phase Error Below 0.4°

The circuit architecture to generate differential CMOS quadrature (I/Q) local oscillator (LO) signals from a differential input at the same frequency is presented. The circuit features an open-loop implementation, which relies on two matched delays and linear phase interpolation. The feasibility of this approach is demonstrated by implementing an I/Q generator covering the operating frequency range from 1 to 3 GHz, manufactured in a 28-nm bulk-CMOS process. The optimum phase accuracy is better than ±0.4° for the entire measured frequency region. A phase noise performance of -163.2 dBc/Hz at 100-MHz offset is achieved at 2 GHz with a power consumption of only 4.4 mW from a 1.1-V supply.

Dual-Channel Phase-Tunable Down Converter With LO Frequency Doubling

A dual-channel phase-tunable down converter with local oscillator (LO) frequency doubling is proposed by using a commercial dual-polarization dual-drive Mach-Zehnder modulator (DP-DMZM) and a specially designed dual-channel phase modulator (DP-PM). A radio frequency (RF) signal is injected to one of sub-DMZMs in the DP-DMZM, and a LO signal modulates another sub-DPMZM. An optical bandpass filter (OBPF) is used to filter out the unwanted sidebands, and only the +2nd-order LO and +1st-order RF sidebands are remained and output to the DP-PM. The DP-PM is composed by two parallel PMs with different modulation efficiency between orthogonal polarizations. Each bias voltage of the DP-PM can linearly vary the phase shift between the RF and LO modulated optical sidebands. After detected by a photodetector, the down converted signal with doubled LO frequency and dual-channel phase shift can be obtained. The principle of the proposed link is verified and the experiments are carried out. The experimental results show that the average spur suppression ratio of the down-converted signals is 29.15 dB. The spurious-free dynamic range (SFDR) of the down converter is 103.94 dB·Hz2/3. The continuous and dependent dual-channel phase shift with the full range of 360° can be experimentally achieved. The proposed down converter integrates multiple function in a link, and has the merit of high electrical purity and convenient operation.

An Energy-Efficient 10-Gb/s CMOS Millimeter-Wave Transceiver With Direct-Modulation Digital Transmitter and I/Q Phase-Coupled Frequency Synthesizer

A fully integrated energy-efficient 10-Gb/s millimeter-wave transceiver with direct-modulation digital transmitter (TX) and I/ Q phase-coupled frequency synthesizer in 65 nm CMOS is presented. The transceiver consists of a direct-conversion receiver (RX), a digital TX with on-chip QPSK modulation, and a quadrature local-oscillation (LO) generation network with a 20-GHz phase-locked loop (PLL) frequency synthesizer. A T/R switch is integrated to interface with an E-shaped patch antenna. The QPSK modulation is directly realized in the I/ Q digital power amplifier (DPA), which simplifies the TX complexity and reduces the power consumption. A 20-GHz sub-sampling PLL (SSPLL) and a quadrature phased-coupled injection-locked oscillator (QILO) are integrated on-chip to generate 60-GHz quadrature LO signals. The QILO utilizes in-phase coupling technique to improve the LO I/ Q matching and phase noise performance. The RX achieves 7.1-dB noise figure (NF) and 25- to 47-dB dynamic gain range. The LO phase noise measured at the TX output is -115.6 dBc/Hz at 10 MHz offset from 60 GHz carrier. The measured error vector magnitude (EVM) of the TX is -23.9 dB for 10-Gb/s QPSK signals at 7-dBm output power. The EVM of the over-the-air (OTA) modulation-demodulation system is -13.8 dB for 10-Gb/s QPSK signals. The transceiver achieves the 10-Gb/s data rate while consuming 340.4 mW. The energy efficiency is 34 pJ/bit. This work demonstrates the fully functional wireless link based on the proposed mm-wave transceiver, which highlights the possibility of energy-efficient solution for future high throughputs mm-wave wireless systems.

True-Time-Delay Beamforming Receiver With RF Re-Sampling

Analog domain true-time-delays (TTD) are desired in hybrid beamforming receivers with large relative bandwidths to mitigate the problem of beam squint. We propose a true-time-delay beamforming receiver architecture which enables squint-free wideband spatial filtering prior to the A/D conversion. The receiver implements true-time-delay with delayed re-sampling of the discrete-time output of a passive mixer. The receiver has the capability to extend the range of the beamforming delays from one to several carrier periods of the RF signal with pulse-skipped local oscillator (LO) signals, thereby enabling TTD beamforming with large antenna arrays. Further, a polyphase structure with parallel mixers is proposed to prevent spectral aliasing resulting from the lowered sample rate of the pulse-skipped LO signals. In addition, the maximum beamforming delay scales with the LO frequency, supporting large arrays also at low frequencies where the antenna separation set by the wavelength is large. We verify the proposed concepts with transistor-level simulation of the receiver implemented with a 28-nm CMOS process. The design achieves a squint-free beamforming for a 400 MHz RF bandwidth, and a maximum beamforming delay of three carrier time periods. The power consumption for a 3 GHz carrier frequency is 4 mW per antenna.

An N-Path Filter Design Methodology With Harmonic Rejection, Power Reduction, Foldback Elimination, and Spectrum Shaping

In this paper, an adaptive design methodology for synthesizing a harmonic free N-path filter with reduced frequency folding is presented. System level analysis of proposed architecture shows that by adding a few extra paths with proper weights to a conventional N-path filter, several characteristics such as harmonic rejection, power reduction, foldback elimination and spectrum shaping can be achieved. The designed filter is reconfigurable to be a band-pass filter (BPF) or a band-reject filter (notch), based on the requirements. By using the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> harmonic of Local Oscillator (LO) signal, instead of the fundamental harmonic, the required input clock frequency in N-phase clock generator is reduced by a factor of n. As a proof of concept, a 0.1-5 GHz RF filter with 75 dB and 82 dB harmonic rejection at 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> and 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> order harmonics respectively is analyzed and simulated using MATLAB and Cadence Spectre-RF. Post-layout simulations are performed using CMOS 180 nm technology with 1.8 V supply voltage. The total power consumption of the chip is less than 8.5 mW while occupying a silicon area of 0.2 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Furthermore, Noise Figure (NF) of the circuit is shown to be between 3.5 and 4.7 dB and its out-of-band IIP3 is +6 dBm.

Linearized analog photonic down-conversion link based on a dual-polarization quadrature phase-shift keying modulator

A novel linearized analog photonic down-conversion link based on an integrated dual-polarization quadrature phase-shift keying (DP-QPSK) modulator is proposed and experimentally verified. Radio frequency and local oscillator signals are fed into the DP-QPSK modulator via an electrical attenuator, respectively. By adjusting the ratio of the two attenuators, the third-order intermodulation distortion can be eliminated based on balanced detection. The scheme is simple and compact and it achieves full spectrum utilization because of using no filter. Experimental results show that the spurious free dynamic range is improved by 16.43 dB for a two-tone signal and the error vector magnitude is improved by 6.16% for a 100-MSym/s 16-quadrature-amplitude-modulation signal.

Design of 0.13 µm low power CMOS subharmonic mixer for DCR applications

ABSTRACT This paper presents a design of 2.4 GHz folded subharmonic active mixer in TSMC 130 nm CMOS process for direct conversion receiver (DCR). To achieve the low supply voltage, the folded topology is adopted for the proposed subharmonic mixer. The complementary current reuse structure is used as RF transconductance stage where the biasing for the PMOS and NMOS transistors are self-biased by a resistor to support high conversion gain at low supply voltage. Frequency doubling operation is done by the mixing core which is driven by a quadrature local oscillator (LO) signals. The proposed mixer is designed and simulated using ADS (Advanced Design System) simulator with Cadence software. It produces 10.5 dB conversion gain, a single sideband) noise figure of 9.5 dB, 2 LO-to-RF isolation of 53 dB, LO-to-RF isolation of 117 dB, RF-to-IF isolation of 55 dB and IIP3 of −7.5 dBm. The quadrature LO subharmonic mixer consumes 824μW power from a supply voltage of 0.8 V. The proposed mixer is compared with existing subharmonic mixers. The comparison shows the proposed subharmonic mixer gives a good Figure of Merit.

Photonic-assisted image rejection mixer based on Hilbert transform in the optical domain using a phase-shifted fiber Bragg grating

A photonic-assisted image rejection mixer is proposed based on Hilbert transform in the optical domain using a phase-shifted fiber Bragg grating (PS-FBG). The image signal and the desired RF signal are converted to the optical domain by carrier-suppressed single-sideband modulation, which is then split into two parts. One part is Hilbert transformed by a specially designed PS-FBG and a 90-deg optical phase shifter and then combined with the other part to directly reject the image signal in the optical domain. The image-free optical signal is downconverted to an intermediate frequency signal by combining it with an optical local oscillator signal and then detecting them in a photodetector. The image rejection capability of the system is analyzed, and an image rejection ratio of 68.0 or 58.6 dB is achieved when the bandwidth of the image signal is 20 or 60 MHz, respectively, while having an acceptable influence on the desired RF signal. Quadrature phase-shift keying (QPSK) signals, 8 phase-shift keying (8PSK) signals, and 16 quadrature amplitude modulation (16-QAM) signals are used to evaluate the image rejection performance. When the bandwidth of the image signal is 18.75 MHz, the error vector magnitudes of the downconverted QPSK, 8PSK, and 16-QAM signals with the same power, modulation format, and bandwidth are 2.5%, 2.5%, and 2.6%, respectively.

A U-Band PLL Using Implicit Distributed Resonators for Sub-THz Wireless Transceivers in 40 nm CMOS

A U-band phase-locked loop (PLL) with implicit distributed resonators in the voltage-controlled oscillator (VCO) and injection-locked frequency divider (ILFD) using 40 nm CMOS is investigated in this brief. While LC -based, transformer-based, and distributed resonators are typically adopted for mm-wave and sub-terahertz applications, implicit distributed resonators are proposed to enhance the oscillation frequency of the VCO and expand the locking range of the ILFD. The operating principles and the characteristics of the proposed implicit distributed resonators are discussed for intuitive insight. The presented PLL occupies 0.53 mm2 core area and has 81.8 mW power consumption. The PLL achieves a measured frequency range of 8.15 GHz (16%) from 46.75 GHz to 54.9 GHz. The measured phase noise is −91.8 dBc/Hz at 1 MHz offset frequency from a carrier of 46.75 GHz. The proposed U-band PLL can provide a clear and stable local oscillation signal for the transceivers operating at mm-wave and sub-terahertz (sub-THz) frequency band.

I/Q Balance-Enhanced Wideband Receiver Front-End for 2G/3G/4G/5G NR Cellular Applications

In this paper, an in-phase (I) and quadrature-phase (Q) balance-enhanced wideband receiver RF front-end is proposed using a quadrature sampling passive mixer configuration, which can be applicable to 2G/3G/4G/5G new radio (NR) applications. Compensating mixer switches are additionally utilized in parallel with main mixer switches in a quadrature mixer for quadrature downconversion. As a consequence, gain and phase errors from the mixer can be mutually compensated at the mixer output, and I/Q imbalance characteristics are significantly improved without an extra calibration process. For the verification of I/Q balancing improvement, the receiver front-end is implemented, which consists of a wideband low noise transconductance amplifier, a double-balanced quadrature sampling passive mixer, transimpedance amplifiers, and quadrature local oscillator signal circuitry. The demonstrated design is fabricated in a 65-nm CMOS process and mainly characterized in long-term evolution (LTE) frequency bands. The implemented design achieves an error-vector magnitude of less than 2% with conversion gains and noise figures of more than 41 dB and less than 4.7 dB for all frequency bands, respectively. Moreover, the design attains in-band and out-of-band IIP3s of higher than −12 dBm and −2.7 dBm for LTE frequency division duplexing test conditions, respectively. The active die area of the implemented receiver front-end is 0.72 mm2. It draws a bias current of 18.2 mA from a nominal supply voltage of 1.2 V.

A Millimeter-Wave Wideband Frequency Conversion Module Based on Waveguide Switched Filters

A wideband frequency conversion module operating at millimeter-wave (MMW) band is proposed in this brief. By up-converting the input intermediate frequency (IF) of 6 GHz with the local oscillator (LO) signal of 13~17 GHz, it can generate the output radio frequency (RF) signal of 32~40 GHz. Firstly, to distinguish the exact position of RF signal from unwanted signal, the detailed spectrum simulation is performed based on the MMW mixer model. After that, some in-band interference signals of 2LO, 3LO-IF and 2LO+2IF overlap with the output RF range are found. To address the issue, a wideband filter is added in LO path to reject LO and 3LO. And more importantly, a switchable waveguide filter integrated in the module is designed to divide the whole RF working band into three sub-bands, thus guaranteeing the output spectrum purity. Through the final measurement, the RF signal power of 6.9~8.5 dBm and the spurious rejection level of 55 dB is obtained.

Phase Locking in Millimeter Wave Frequency Synthesizers - Design overview of Charge Pump Phase Locked Loops

Phase Locked Loops are key blocks which are widely adopted in all area of electronics, especially transceivers in wireless communication systems. The application of Phase Locked Loop varies from generation of local oscillator signal for upconversion and down conversion, generation and distribution of clock signals and jitter reduction. The most extensive use of Phase Locked Loop is for frequency synthesis. The requirements of synthesizer architectures depend on various system requirements and specifications which are based on regulatory standards. The design of Phase Locked Loop components involves the consideration of various techniques to resolve the nonidealities at front end high frequency components as well as back end low frequency components. This paper presents the background and importance of a Phase Locked Loop, various approaches over the years, design choices for each block and practical design methodology for Charge Pump Phase Locked Loops. This paper also presents the system level design of Phase Locked Loop and supply noise interactions among sub modules inside a charge pump Phase Locked Loop