Frequency-modulated Continuous-wave Chirp Research Articles

Ultra-broadband multi-tone frequency measurement based on the recirculating frequency shift of a frequency modulated continuous wave

We proposed an ultra-broadband multi-tone frequency measurement (FM) approach based on frequency modulated continuous wave (FMCW). This work aims to achieve wide-range multi-tone FM without image interference, using electrical components with narrow bandwidth and low sampling rate, while maintaining high FM accuracy. The FM range is largely increased by extending the bandwidth of the optical FMCW through a recirculating frequency shift (RFS) loop, from 0.001 GHz-16 GHz to 0.001 GHz-437.5 GHz. The bandwidth-extended optical FMCW coherently beats with a continuous wave (CW) light modulated by the signal under test (SUT) at the balanced photodetector (BPD). The following low-pass filter (LPF) outputs pulses at the time when the frequencies of FMCW and SUT are equal, constructing frequency-to-time mapping (FTTM). Owing to the zero-intermediate-frequency (zero-IF) architecture, image interference is avoided. In addition, the up- and down-chirps of FMCW are used to achieve self-reference, avoiding the utilizing of reference signals, which realizes high FM accuracy. In the experiment, a FM within 0.1 GHz-43.5 GHz is demonstrated using an available microwave generator (MG) with a maximum output frequency of 43.5 GHz. The FM errors are kept within ±10 MHz for all frequencies with a mean and standard deviation of −0.3 MHz and 3.17 MHz, respectively. The multi-tone resolution is about 60 MHz at the FMCW chirp rate of 3.1998 GHz/μs, which is consistent with the theoretical result. According to the theoretical derivation, the multi-tone resolution can be improved to 1 MHz by lowering the FMCW chirp rate.

An event‐driven model of fractional‐N CPPLL based FMCW synthesizers

AbstractThis paper proposes an improved event‐driven (ED) model to improve the simulation efficiency of a mixed‐signal charge‐pump phase locked loop (CP‐PLL) design for a frequency‐modulated continuous‐wave (FMCW) chirp generation. The improvement mainly comes into three parts. First, we update the data only when it changes during the previous trigger. Second, we save the data at the triggering moment of the reference clock to achieve uniform sampling for better noise characterization. Furthermore, we propose a simplified model that is specifically optimized for the third‐order loop filter (LF). This article presents a detailed design flow of the improved ED model, and we apply it to the simulation of the FMCW chirp generation. Compared to the conventional transistor‐level simulation, our proposed model reduces the simulation time to less than 1 s, which leads to a reduction of the simulation time by five or six orders of magnitude.

A D-Band Joint Radar-Communication CMOS Transceiver

A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D$ </tex-math></inline-formula> -band joint radar-communication complementary metal–oxide–semiconductor (CMOS) transceiver featuring a dual-function mode multiplexer, a power-combining PA with high output power, a current choking high-gain mixer, a two-point modulation (TPM) frequency-modulated continuous-wave (FMCW) digital phase-locked loop (PLL) with a dual-core DCO, and a wideband I/Q local oscillator (LO) generator is implemented in 28-nm CMOS technology. In the radar mode, the RF front end demonstrates 46-GHz bandwidth (BW), and the on-chip PLL/LO generated FMCW chirp achieves a BW of 30 GHz and a slope of 30 GHz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50~\mu \text{s}$ </tex-math></inline-formula> . In the communication mode, the transceiver including the analog baseband realizes 20-GHz BW, and the image rejection ratio (IRR) is better than 40 dB. The measured transmitter (TX) saturated output power is 13 dBm, and the output 1-dB compression point (OP1dB) is 8.3 dBm. The measured typical PLL phase noise is −111.3 dBc/Hz at a 1-MHz offset from an 11.69-GHz carrier frequency. The TX-to-RX over-the-air (OTA) modulation–demodulation measurement with QPSK and 16-QAM signals shows the error vector magnitude (EVM) of −16.5 and −19.7 dB, respectively.

A 140-GHz FMCW TX/RX-Antenna-Sharing Transceiver With Low-Inherent-Loss Duplexing and Adaptive Self-Interference Cancellation

This article presents a 140-GHz frequency-modulated continuous-wave (FMCW) radar transceiver featuring transmit/receive (TX/RX) antenna sharing that address a TX/RX beam misalignment problem when large-aperture lenses/mirrors/reflectarrays are used for pencil beam forming. A full-duplexing technique based on circular polarization and geometrical symmetry is applied to mitigate the 3 dB + 3 dB insertion loss inherent to conventionally adopted directional couplers, while still maintaining high TX-to-RX isolation. In addition, a self-adaptive self-interference cancellation (SIC) is implemented to suppress extra leakage due to antenna mismatch from a desired frontside radiation scheme. The TX/RX antenna sharing enables the pairing with a large 3-D printed planar lens and boosts the measured effective isotropic radiated power (EIRP) to 25.2 dBm. The measured total radiated power and minimum single-sideband noise figure (SSB NF) including antenna and duplexer losses are 6.2 dBm and 20.2 dB, respectively. The measured total TX-RX isolation is 33.3 dB under 14-GHz wide FMCW chirps. Based on a 65-nm complimentary metal–oxide–semiconductor (CMOS) technology, the chip has a die area of 3.1 mm2 and consumes 405 mW of dc power. Among all reported sub-THz transceivers with TX/RX antenna sharing, this work demonstrates the highest total radiated power and is the only work that has >30 dB of TX-RX isolation while mitigating the inherent 6 dB coupler loss.

A 2.3 GHz 2.8 mW Sampling ΔΣ PLL Achieving −110 dBc/Hz In-Band Phase Noise and 500 MHz FMCW Chirp

A phase interpolator (PI)-free fractional- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> sampling phase-locked loop (SPLL) has been proposed and implemented in 130 nm CMOS technology, which eliminates time-domain PI, digital-to-time converter (DTC), or background calibration. This phase-locked loop (PLL) employs two linear slope generators (LSGs) to produce linear waveforms, which are related to the VCO feedback phase. Then the reference directly samples the LSG outputs to obtain the phase error. Following this, a 3 bit DAC-based phase interpolating charge pump (PICP) is utilized to interpolate the phase error before feeding it to the loop filter. This enables the SPLL to achieve a fractional- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> ratio without any DTC or calibration. On-chip frequency-modulated continuous-wave (FMCW) chirp generation is also included, which provides 500 MHz FMCW chirp with reconfigurable chirp rate and up to 25% chirp bandwidth to carrier frequency ratio. It consumes 2.8 mW from a 1.2 V supply and occupies an active area of about 0.4 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . With a 50 MHz crystal reference, the in-band phase noise is measured to be 109 dBc/Hz at 200 kHz offset. The FoM for the system is measured as −243~ −247.5 dB.

Phase-Extraction Method With Multiple Frequencies of FMCW Radar for Human Body Motion Tracking

A phase-extraction technique with multiple frequencies of a frequency-modulated continuous-wave (FMCW) radar is proposed, which allows the detection of target motions exactly. An FMCW chirp signal is decomposed into multiple-frequency continuous-wave (CW) signals to extract modulated phases due to target motions. The demodulated phases at multiple frequencies are summed and averaged. Since the proposed method can extract the phase without performing a fast Fourier transform (FFT), it can overcome the range migration problem, which causes an error in phase extraction using a conventional FFT-based method. Therefore, the proposed method can reduce spurious noises induced by phase errors compared with the conventional method. This was verified experimentally for both human vital sign detection and body motion tracking.

A CMOS 76–81-GHz 2-TX 3-RX FMCW Radar Transceiver Based on Mixed-Mode PLL Chirp Generator

A fully integrated 76–81-GHz frequency-modulated, continuous-wave (FMCW) radar transceiver (TRX) in a 65-nm CMOS is presented. Two transmitters (TXs) and three receivers (RXs) are integrated for multiple-input multiple-output (MIMO) processing. A 38.5-GHz mixed-mode phase-locked loop (PLL) with reconfigurable loop bandwidth and a frequency doubling scheme are employed to generate the reconfigurable FMCW chirp waveforms. The coarse-to-fine-segmented current DAC is utilized to support sawtooth FMCW chirps with fast frequency ramping-down capability, and the delay lock loop (DLL)-based delay time calibration is used to improve the linearity of the embedded 2-D Vernier time-to-digital converter (TDC). Passive voltage-mode down-conversion is utilized to improve the RX linearity against TX leakage and short-range interference. A bottom-switching Gilbert-type modulator in the TX is proposed to realize the bi-phase modulation, and the magnetically coupled resonator technique is used to effectively expand the link bandwidth. The measurement results show that the FMCW TRX could generate reconfigurable chirps with the bandwidth from 250 MHz to 4 GHz and the period from 30 $\mu \text{s}$ to 10 ms. The root-mean-square (rms) frequency error is 110 kHz for a sawtooth chirp with 4-GHz bandwidth and 300- $\mu \text{s}$ period. The TX maximum output power is 13.4 dBm and is adjustable within 3 dB by reconfiguring its low dropout regulator (LDO) voltage. The RX achieves a 15.3-dB noise figure at 600-kHz IF and a −8.5-dBm RF input-referred P1dB. The overall power consumption is 921 mW, with two TXs and three RXs powered ON. Based on the proposed TRX chip, prototype hardware and a data process algorithm are developed. Real-time experimental results show that the distance and the angular resolution of the MIMO radar achieved are 5 cm and 9°, respectively.

A 77-GHz Mixed-Mode FMCW Generator Based on a Vernier TDC With Dual Rising-Edge Fractional-Phase Detector

A 77-GHz frequency-modulated continuous-wave (FMCW) generator is presented for millimeter-wave (mm-wave) radar applications. The FMCW chirp is provided by a mixed-mode phase-locked loop (PLL). A dual rising-edge fractional-phase detector based on time-to-digital converter (TDC) is proposed to overcome the problem caused by the rising and falling time mismatch. A 2.3 ns detection range, 10 ps resolution Vernier TDC is employed in the detector to cover the two consecutive rising edges with less power consumption. A self-calibrated delay chain is employed in the Vernier TDC to overcome process, voltage and temperature (PVT) variations. Furthermore, sampling-edge selection technique is utilized to avoid the glitch during phase detection. A divider-less frequency error estimator is presented to save area and power. By employing a coarse-fine segmented digital-to-analog converter (DAC), the generator supports triangular and sawtooth-like FMCW chirp with reconfigurable period and bandwidth. An LC voltage- controlled oscillator (VCO) with split varactor is proposed to improve the linear tuning range. Implemented in 65 nm CMOS, the FMCW generator consumes 99 mW power and 0.7 mm $\times $ 0.8 mm chip area. The measurement results show that the phase noise from 78.7 GHz carrier is −87.4-dBc/Hz at 1 MHz offset. The measured root-mean-square (RMS) frequency error of a sawtooth-like FMCW chirp with 4 GHz bandwidth and 0.1 ms period is 205 kHz.

A Study of Phase Noise and Frequency Error of a Fractional-N PLL in the Course of FMCW Chirp Generation

This paper presents the theoretical and experimental results on the phase noise spectrum and the rms frequency error of a fractional-N phase-locked loop (PLL) under frequency-modulated continuous-wave (FMCW) chirp generation. The phase noise spectrum under modulation is analytically calculated for a second-order charge pump PLL with a feedback divider ratio linearly changing over time. This is followed by an analysis of the steady-state rms frequency error of the output frequency after PLL settling is achieved during chirp generation. A fractional-N PLL with integrated frequency ramp generator is presented. Phase noise and jitter measurements on the PLL under modulation are performed at the output of the programmable feedback divider. The resulting low-frequency rms jitter is reduced by about 9dB with doubling the charge pump current, and reduced by about 6dB with halving the ramp slope. The rms frequency error under FMCW modulation is measured at the modulated voltage-controlled oscillator output. The dependence of the frequency error on the loop filter capacitance for various ramp slopes is given. A frequency error of 112kHz is achieved with a ramp slope of 1.28GHz/80 μs at a carrier frequency of 62GHz. The noise measurements are in good agreement with the developed phase noise model. A programmable loop filter capacitance is suggested to accommodate the static phase offset and the resulting noise performance to the ramp slope.

A Multi-Carrier-Frequency Random-Transmission Chirp Sequence for TDM MIMO Automotive Radar

The collocated time-division multiplexing (TDM) multiple-input multiple-output (MIMO) technique and frequency-modulated continuous-wave (FMCW) chirp sequence are widely used in automotive radar because of the low hardware complexity and the high-accurate range and velocity measurements. In conventional TDM chirp sequences, the transmitters are switched according to their natural spatial order (referred to as a fixed sequential order), thereby inducing space-Doppler frequency coupling and a relatively low unambiguous Doppler interval. In this paper, a new FMCW chirp sequence and corresponding signal processing method for TDM MIMO automotive radar are proposed. The novel waveform adopts the concept of random transmission to distort the linear phase relationship between space and Doppler, therefore, overcoming the coupling problem. Then, via compressed sensing processing, the scheme can suppress the sidelobe pedestal arisen in the conventional matched filter for targets detection. Besides, based on multiple-frequency observations of the same targets, the velocity ambiguity can be adequately resolved. Compared with conventional chirp sequence, the proposed scheme simultaneously overcomes the typical TDM MIMO chirp sequence problems, thereby avoiding a reduction in the data rate. Also, the scheme significantly reduces the mutual interference between adjacent systems. The simulations and experimental results demonstrate the effectiveness of the proposed chirp sequence scheme.

A 260-mW Ku-Band FMCW Transceiver for Synthetic Aperture Radar Sensor With 1.48-GHz Bandwidth in 65-nm CMOS Technology

Monolithic integration of synthetic aperture radar (SAR) transceiver with small size, lightweight, and low power consumption is suitable for uploading to a compact unmanned aerial vehicle (UAV) for SAR imaging. This paper presents a monolithic frequency-modulated continuous-wave (FMCW) SAR transceiver that works at Ku-band and centers at 15 GHz. Techniques to address the special requirements of UAV SAR are proposed. A digital-tunable mixed-signal-mode FMCW chirp synthesizer is designed to be power efficient, to provide a tunable chirp rate, and to enable digital minimization of the root-mean-square (RMS) frequency errors. A saturated driver-amplifier-power-amplifier chain and an input-load peak-staggering low-noise amplifier are implemented to nullify the ripple effects so that the degradations of imaging performances can be prevented. Moreover, a 12th order active-RC bandpass filter is used to suppress the intermediate frequency interferences of both ground reflections and antenna leakage. A binary-weighted programmable gain amplifier and a successive approximation analog-to-digital converter are also integrated into the chip. Fabricated using a 65-nm complementary metal-oxide-semiconductor technology, the prototype demonstrates 1.48-GHz chirp bandwidth and <186-kHz rms frequency errors in a programmable modulation period from 1.18 to 10 ms. The transmitter and receiver RF front end attains 1.1- and 0.51-dB ripples, respectively. The function of the FMCW SAR transceiver is validated through the delay line and near-field ranging tests. The SAR imaging experiment with a distance of around 110 m is successfully carried out using the chip prototype and a range migration algorithm. At 1.2-V supply, the transceiver chip consumes 259.4 mW.

A 77 GHz FMCW radar transmitter with reconfigurable power amplifier in 65 nm CMOS

A frequency modulated continuous-wave (FMCW) radar transmitter in 65nm CMOS is presented. The transmitter consists of one FMCW signal generator, one reconfigurable power amplifier and bias circuits. FMCW chirp signal comes from a sigma-delta modulated fractional-N phase-locked loop (PLL) with an integrated digital triangle-wave generator to control the output division-ratio of the sigma-delta modulator. A four-way power combining power amplifier is employed to improve the output power with a reconfigurable output power to satisfy different detection distance requirements. The measured results show that the chirp bandwidth achieves 2GHz, from 76GHz to 78GHz, and the power amplifier achieves 13.1dBm output P1dB with 8.1% PAE. The power amplifier and FMCW signal generator consume 228mW and 56mW power, respectively, with a 1.0V power supply. The core die area is only 2.6×0.88mm2.

Rapid‐run ionosonde observations of traveling ionospheric disturbances in the auroral ionosphere

AbstractSince 2007, the Sodankylä Geophysical Observatory routinely performs vertical ionosphere soundings once per minute, using a frequency‐modulated continuous‐wave chirp at the rate of 500 kHz/s from 500 kHz to 16 MHz. We used these data to study traveling ionospheric disturbances (TIDs) during 10–16 local time. The observations were made between April 2007 and June 2012, mostly during low solar activity. The TIDs were studied in five bands of periods corresponding to the following: infrasonic (acoustic) waves and the buoyancy cutoff (periods from 5 to 10 min); small‐scale gravity waves (GWs; 10–15 min); medium‐scale (MS; 15–30 min) GWs; medium‐large scale (MS‐LS; 30–60 min) GWs; and large‐scale (LS; 60–120 min) GWs. Relative contribution (with respect to LS TIDs) of the short‐period (5–15 min) and MS (15–30 min) TIDs shows minima in winter and maxima in summer. These annual variations anticorrelate with variations of true height, namely, the largest relative amplitudes occur in summer, when TIDs were observed at minimal heights. We suggest that the summer increase of shorter‐period TIDs is due to lowering reflection to the height where the Brunt‐Väisälä period is smaller and, hence, shorter‐period gravity waves exist. The summer maxima were most prominent during the 3 years of minimal solar activity (2008–2010). In 2011, when solar activity increased, the annual variation seems less prominent. Annual variations of the longer‐period (30–120 min) TIDs are essentially less significant. For all TIDs, no obvious dependences on the AE and Ap indices of magnetic activity were found.

A 77 GHz 90 nm CMOS Transceiver for FMCW Radar Applications

The first 77 GHz frequency modulated continuous wave (FMCW) radar transceiver IC with an accurate FMCW chirp signal generator using a 90 nm CMOS process is presented. To realize accurate FMCW radar system in CMOS, a PLL synthesizer based FMCW generator with chirp smoothing technique that is able to output linear FMCW frequency chirp using a nonlinear reference chirp signal supplied from a low spec/cost digital-oriented frequency reference is applied. The fabricated IC consists of an LNA, a down-conversion mixer with an output buffer, a driver amplifier, a power amplifier with power combiner, an LO distributer and an FMCW synthesizer. The measured FMCW signal from the proposed FMCW generator achieves 93 kHz frequency error (nonlinearity) at the 77 GHz chip signal. Radar performance of the IC has less than 1% ranging error from 1 m to 8 m distance from the measurement in a laboratory. These results show the transceiver achieves a fundamental function for radar applications with 520 mW power consumptions.