Digital Intermediate Frequency Research Articles

A novel digital intermediate frequency module for hyperspectral microwave radiometers based on the parallel fast Fourier transform algorithm.

Microwave radiometers, possessing all-day and all-weather operational capabilities, are extensively utilized in the exploration of planetary atmospheres and surfaces. The potential of the hyperspectral detection technology to enhance the precision and resolution of microwave radiometer detection has made it a crucial research focus. This paper introduces an intermediate frequency (IF) module for hyperspectral microwave radiometers. The IF module is constructed with two 6.4 gigabit samples per second sampling-rate analog-to-digital converter (ADC) chips and a Xilinx Virtex-7 field programmable gate array. By implementing a parallel fast Fourier transform algorithm and a pipeline architecture, the IF module can efficiently process all ADC sampling data in real-time, generating 512 channels of output for each ADC. The test results, including linearity, sensitivity, and flatness, are presented and thoroughly analyzed for the IF module. Furthermore, the module is interfaced with the radio frequency front-end of the microwave radiometer to measure hot and cold calibration sources and assess its sensitivity. When combined with a suitable front-end receiver, the IF module can form a radiometer system suitable for various applications of microwave remote sensing.

Acquisition of Weak BDS Signal in the Lunar Environment

Autonomous navigation using the GNSS has been increasingly used in lunar exploration missions, as it is considered an efficient method for spacecraft to operate without relying on ground facilities. However, so far, only GPS and Galileo have been studied and implemented in lunar missions, whereas the potential of BDS-3 for such missions remains largely unexplored. This paper presents an analysis and evaluation of the navigation service capabilities for spacecraft at lunar altitudes by utilizing existing GNSS satellite resources in orbit. In detail, we investigate the number of GNSS signals received by low lunar orbit (LLO) receivers, as well as the carrier-to-noise ratio (C/N0), Doppler shift, and geometric dilution of precision (GDOP) of the received signal. Additionally, a digital intermediate frequency (IF) signal simulation program to emulate the BDS B1I signal is utilized, which allows to freely set the carrier-to-noise ratio, Doppler shift, and code phase. Based on this framework, we discussed a high-sensitivity BDS B1I signal receiver and validated its performance with simulated signals. We verified the capabilities of coherent integration, non-coherent integration, differential integration, and semi-bit methods to detect weak BDS B1I signals in a lunar environment. The results indicate that the semi-bit coherent differential integration method is still capable of acquiring signals at a C/N0 of 15 dB-Hz and can effectively suppress the navigation data bit sign transition.

Comparison of Radio Interferometers with Analog and Digital Extraction of Recorded Signal

Introduction. Radio telescopes of Very Long Baseline Interferometry (VLBI) networks usually record several signals with relatively narrow (up to 32 MHz) bands, which are extracted by means of base band converters (BBC) from an analog noise signal of an intermediate frequency (IF) with bands up to 1 GHz. When processing data, frequency band synthesis is used. At new small radio telescopes (for example, RT-13), directly wideband IF signals are digitized. An ability to connect the RT-13 radio telescope to the “Quasar” VLBI complex and to international VLBI networks provides by a digital narrow-band signal extraction module developed in 2019.Aim. Determining the measuring accuracy of an interferometric group delay of a signal by a radio interferometer with a digital narrow-band signal extraction module and comparing the sensitivity of interferometers with analog and digital signal extraction systems.Materials and methods. Sensitivity losses of interferometers with different systems for detecting recorded signals were calculated. The accuracy of a multi-channel interferometer with the synthesis of a frequency band and of an interferometer with recording of digital broadband IF signals without band synthesis was compared. The results were confirmed by VLBI observations in the observatories of the “Quasar” complex.Results. When replacing the analog system of signal extraction with digital system the sensitivity losses of the interferometer were slightly reduced. The measurement accuracy of the interferometric group delay had not changed. Accuracy increased when digitally recording broadband IF signals and when synthesizing a frequency band significantly larger than the IF bandwidth. Conditions and minimum synthesized bands were determined under which the accuracy of the interferometer with the registration of narrowband signals can be higher than the accuracy of the interferometer with the registration of wideband IF signals.Conclusion. The problem of combining RT-13 radio telescopes with VLBI networks with recording of video frequency signals was solved. The efficiency of the installation of digital signal conversion systems at radio telescopes was shown.

A Novel High-Pass Delta–Sigma Modulator-Based Digital-IF Transmitter With Enhanced Performance for SDR Applications

This brief presents a new transmitter architecture based on digital-intermediate frequency (IF) high-pass delta–sigma modulator (HPDSM). The proposed digital-IF transmitter topology utilizes a novel complex HPDSM topology to address the high quantization-noise power problem in Cartesian band-pass BPDSM and HPDSM-based digital-IF transmitters, without increasing the oversampling ratio of the signal or the clock rate of the system. To evaluate the performance of the new digital-IF transmitter system, a comparison with its Cartesian band-pass and high-pass counterparts, in terms of signal to noise and distortion radio (SNDR) and coding efficiency, was established. A simulation using 8 dB peak to average power ratio long term evolution signals with 1.24-MHz bandwidth showed that by integrating the proposed second-order complex HPDSM digital-IF in the transmitter, the power of the quantization noise is significantly reduced. The transmitter digital blocks were implemented on the BEEcube software-defined radio prototyping platform. The input signal is encoded by the new HPDSM topology and is up-converted and then fed to the inverse class-F switch-mode power amplifier. An overall efficiency of 12% was achieved by the proposed topology. Moreover, the output signal SNDR reached 37.8 dB and the adjacent channel leakage ratio at the lower and upper 1.25-MHz offset frequencies measured is equal to −35 dBc.

A re-configurable MASH 2-2 bandpass DQEFM for multi-standard applications

ABSTRACTThe design, analysis and implementation of a multi-stage noise shaping (MASH) bandpass modulator that employs a differentially quantized error feedback modulator (DQEFM) structure is described. The re-configurability, reduction of power-hungry active blocks and reduced sensitivity to circuit non-idealities makes this proposed bandpass modulator a suitable candidate for a digital intermediate frequency receiver system. The mathematical analysis and simulation results indicate the resemblance of the proposed modulator with the conventional sigma-delta modulator. The circuit level simulations indicate the better performance of the proposed modulator in terms of hardware complexity and power. The proposed cascaded modulator when implemented using 45nm CMOS process attains a signal-to-noise plus distortion ratio of 81.4 dB for a bandwidth of 200 kHz (GSM) and 61 dB for a bandwidth of 5 MHz (WCDMA). The circuit level simulation of the proposed bandpass architecture indicates a power consumption of 3.7 mW and 6.9 mW for GSM and WCDMA modes with 1V supply.

Design of Reconfigurable Digital IF Filter With Low Complexity

Due to limited frequency resources, new services are being applied to the existing frequencies, and service providers are allocating some of the existing frequencies for newly enhanced mobile communications. Because of this frequency environment, repeater and base station systems for mobile communications are becoming more complicated, and frequency interference caused by multiple bands and services is getting worse. Therefore, a heterodyne receiver using intermediate frequency (IF) filters with high selectivity has been used to minimize the interference between frequencies. However, repeater and base station systems in mobile communications employing fixed IF filters cannot actively cope with the usage of multiple frequency bands, the application of various services, and frequency recycling. Therefore, this brief proposes a reconfigurable digital IF filter with variable center frequency and bandwidth while achieving high selectivity as existing IF filters. The center frequency of a filter can vary from 10 MHz to 62.5 MHz, and the filter bandwidth can be selective to one of 10 MHz, 15 MHz, and 20 MHz. The proposed digital filter also reduces the complexity of adders and multipliers by 38.81% and 41.57%, respectively, compared to an existing digital filter by using a filter bank and a multi stage structure. This digital IF filter is fabricated on a 130-nm CMOS process and occupies 5.90 mm2.

GNSS IF Signal Simulation Considering Oscillator Phase Noise

Oscillator phase noise has a negative effect on the tracking performance of Global Navigation Satellite System (GNSS) receivers. To provide GNSS software receivers with real test environments, this paper proposes a method to simulate the GNSS Intermediate Frequency (IF) signal, taking the oscillator phase noise effect into consideration. The oscillator parameters are first measured via a pseudolite transmitter and receiver system. According to the measured oscillator parameters, an oscillator-induced frequency fluctuation is then generated, and added to the digital IF signal. Further simulation experiments are conducted that attempt to measure the oscillator phase noise effect on a second-order Phase Lock Loop (PLL) performance. Results indicate that the IF signal simulator considering the oscillator phase noise is able to provide software receivers with real signal dynamics, helping to evaluate the performance of signal processing algorithms on a software platform.

基于数字零中频纳米位移遥测技术研究

基于数字零中频纳米位移遥测技术研究

Noncontact Physiological Dynamics Detection Using Low-power Digital-IF Doppler Radar

The instantaneous vital sign rates, which are related to physiological dynamics, are important indicators of human health condition. This paper presents a noncontact way to measure the human instantaneous vital signs using digital-intermediate frequency (IF) Doppler radar. The synchrosqueezing transform-based algorithm has been proposed to get a concentrated time-frequency (TF) distribution, so that the high-resolution instantaneous heartbeat and respiratory rates and the time-domain signals can be acquired. Moreover, the developed radar with customized radio frequency module employs the direct IF sampling technique to achieve high sensitivity to capture the tiny vital sign variations. Experiments with different human subjects and physiological conditions have been carried out. Compared with the landmark-based method and traditional TF algorithms, the results show that instantaneous vital signs can be acquired more accurately within 3 m at a -13 dBm transmit power by the proposed method. Therefore, the radar can be used for evaluating the physiological dynamics and assessing health condition.

All-optical, ultra-wideband microwave I/Q mixer and image-reject frequency down-converter.

An all-optical and ultra-wideband microwave in-phase/quadrature (I/Q) mixer, based on a dual-parallel Mach-Zehnder modulator and a wavelength division multiplexer, is proposed. Due to the simultaneous frequency down-conversion and 360-deg tunable phase shifting in the optical domain, the proposed I/Q mixer has the advantages of high conversion gain and excellent quadrature phase balance (<±1.3 deg⁡) with a wide operating frequency from 10 to 40GHz. Assisted by an analog or digital intermediate-frequency quadrature coupler, an image-reject frequency down-converter is then implemented, with an image rejection exceeding 50dB over the working band.

Real-Time Generation and Reception of OFDM Signals for $X$ -Band RoF Uplink With Heterodyne Detection

A field-programmable gate arrays-based real-time orthogonal frequency-division multiplexing (OFDM) transceiver is implemented for the uplink of an $X$ -band radio-over-fiber (RoF) system with heterodyne detection for the first time. Digital intermediate-frequency $I/Q$ modulation and demodulation, and forward error correction are applied. Minn’s timing synchronization method is slightly modified with reduced implementation complexity for the proposed OFDM-RoF system. By using Reed–Solomon code with symbol interleaving technique, the real-time transmission of the $X$ -band 16-ary quadrature amplitude modulation OFDM-RoF signal over 10-m wireless and 2.26-km single mode fiber link is successfully achieved with a post-FEC bit error rate below $1\times 10^{-9}$ .

Comparison and Realization of Fast Acquisition Method for GPS Signal under High Dynamic

In order to solve the problem of fast acquisition for GPS signal under high dynamic, the paper add window in traditional Partial Matched Filter (PMF) plus Fast Fourier Transform (FFT) for fast acquisition with the purpose of reducing the scalloping loss and improving the acquisition performance. And comparing the parallel code phase acquisition based on FFT with the new acquisition method based on the improved PMF+FFT. The high dynamic digital intermediate frequency signal is generated based on high dynamic trail. For the quicker acquisition speed, a method of fast blind search combining pseudo code correlation is used in acquisition. The results of simulation based on Matlab show that the new acquisition method can achieve the performance of 100g dynamics.

Sample-Wise Aiding in GPS/INS Ultra-Tight Integration for High-Dynamic, High-Precision Tracking.

By aiding GPS receiver tracking loops with INS estimates of signal dynamics, GPS/INS ultra-tight coupling can improve the navigation performance in challenging environments. Traditionally the INS data are injected into the loops once every loop update interval, which limits the levels of dynamics accommodated. This paper presents a sample-wise aiding method, which interpolates the aiding Doppler into each digital sample of the local signal to further eliminate the dynamic errors. The relationship between the tracking error and the aiding rate is derived analytically. Moreover, the effects of sample-wise aiding using linear and spline interpolations are simulated and compared with traditional aiding under different INS data update rates. Finally, extensive tests based on a digital IF (intermediate frequency) signal simulator and a software receiver validate the theoretical equations and demonstrate that the dynamic stress error can be significantly reduced by sample-wise aiding.

The Design of Radar Digital Intermediate Frequency Test System

To satisfy the requirement of high performance signal processing technique, it is necessary to use the direct sampling of intermediate frequency signal to obtain quadrature signals. Digital intermediate frequency (DIF) system is widely used in radar and communication system. This paper briefly introduces the principle of test system based on DIF. We design this DIF test system to test the performance of ADC and I/Q. The design has the advantages of convenient use, and reliable performance.

A high-field magnetic resonance imaging spectrometer using an oven-controlled crystal oscillator as the local oscillator of its radio frequency transceiver

A home-made high-field magnetic resonance imaging (MRI) spectrometer with multiple receiving channels is described. The radio frequency (RF) transceiver of the spectrometer consists of digital intermediate frequency (IF) circuits and corresponding mixing circuits. A direct digital synthesis device is employed to generate the IF pulse; the IF signal from a down-conversion circuit is sampled and followed by digital quadrature detection. Both the IF generation and the IF sampling use a 50 MHz clock. An oven-controlled crystal oscillator, which has outstanding spectral purity and a compact circuit, is used as the local oscillator of the RF transceiver. A digital signal processor works as the pulse programmer of the spectrometer, as a result, 32 control lines can be generated simultaneously while an event is triggered. Field programmable gate array devices are utilized as the auxiliary controllers of the IF generation, IF receiving, and gradient control. High performance, including 1 μs time resolution of the soft pulse, 1 MHz receiving bandwidth, and 1 μs time resolution of the gradient waveform, is achieved. High-quality images on a 1.5 T MRI system using the spectrometer are obtained.

Polar Transmitter with Differential DSM Phase and Digital PWM Envelope

A low-power low-cost polar transmitter for EDGE is designed in 0.18μm CMOS. A differential delta-sigma modulator (DSM) tunes a three-terminal voltage-controlled oscillator (VCO) to perform RF phase modulation, where the VCO tuning curve is digitally pre-compensated for high linearity and the carrier frequency is calibrated by a dual-mode lowpower frequency-locked loop (FLL). A digital intermediate-frequency (IF) pulse-width5 modulator (PWM) drives a complementary power-switch followed by an LC filter to achieve envelope modulation with high efficiency. The proposed transmitter with 9mW power dissipation relaxes the time alignment between the phase and envelope modulations, and achieves an error vector magnitude (EVM) of 4% and phase noise of ?123dBc/Hz at 400kHz offset frequency.

A Generalized Architecture for the Frequency- Selective Digital Predistortion Linearization Technique

This paper presents a new architecture for the frequency-selective digital predistortion (DPD) for two- and three-band power amplifier (PA) linearization. Also, largely spaced-signal DPD using a digital intermediate frequency (IF) technique is demonstrated. The algorithm used accounts for differential memory effects up to fifth order for bands that can be arbitrarily spaced. The simulation and experimental studies are performed using various signal sets; two- and three-band multitone signals with various tone spacing, band separation, and complementary cumulative distribution function. An improvement of 10 dB over third-order linearization is demonstrated in simulation for more than 20 dB of adjacent channel power ratio reduction. The test signal and the linearization algorithm were implemented on a field-programmable gate array. The linearization algorithm was applied to an RF amplifier at 700-900 MHz. For the two-band case, more than 15 dB on the in-band, 13 dB on the third, and 5 dB on the fifth intermodulation distortion (IMD) cancellation were achieved. For the three-band case, more than 12 dB of IMD cancellation was observed. For largely spaced signal DPD, more than 15 dB of IMD cancellation was achieved. In the three-band case, the linearization of intermodulation byproducts overlapping with the in-band distortion is found to be of critical importance.

Performance Optimization of Digital Spectrum Analyzer With Gaussian Input Signal

Analog to digital converters (ADC) and cascade integrator-comb (CIC) filters are the basic modules in a digital intermediate frequency (IF) spectrum analyzer. The optimal output signal-to-noise ratio (SNR) of the digital IF spectrum analyzer with the Gaussian input signal is considered in this letter. The idea is to strike a trade-off between the saturation error and granular error when quantizing the Gaussian input signal. This letter firstly derives a relationship among the maximum allowed input signal amplitude, input signal power, ADC quantization bits and optimal quantization SNR. Besides, an optimal clipping strategy for the CIC decimation filter with variable decimation rates is proposed. Both numerical and simulation results are presented to demonstrate that the proposed clipping method is able to achieve significant SNR gain compared with the traditional rounding or truncation method.

Polynomial based Design of CIC Compensation Filter used in Software Defined Radio for Multirate Signal Processing

oftware defined radio has find important place in modern communication systems where majority of signal processing is performed in the digital domain using programmable DSPs.Digital down conversion (DDC) is one of the core technologies in SDR, as well as an important component of digital intermediate frequency receiver system. DDC use CIC decimation filters for sample rate decimation. CIC decimation filters require less computation but large passband droop occurs in the frequency response. This paper presents a simple design of compensation FIR filter for CIC decimation filter which will correct the passband droop. Compensation filter design consists of polynomial based design of FIR filter which are used in cascade with CIC filter. As proposed filter depends on simple transformation less approach and computation is required. The resulting structure is multiplier less and exhibits small passband droop in comparison to CIC filter. It modifies the frequency response of CIC decimation filter while maintaining the linear phase.

Sampling Jitter Effect on a Reconfigurable Digital IF Transceiver to WiMAX and HSDPA

This paper outlines the time jitter effect of a sampling clock on a software-defined radio technology-based digital intermediate frequency (IF) transceiver for a mobile communication base station. The implemented digital IF transceiver is reconfigurable to high-speed data packet access (HSDPA) and three bandwidth profiles: 1.75 MHz, 3.5 MHz, and 7 MHz, each incorporating the IEEE 802.16d worldwide interoperability for microwave access (WiMAX) standard. This paper examines the relationship between the signal-to-noise ratio (SNR) characteristics of a digital IF transceiver with an under-sampling scheme and the sampling jitter effect on a multichannel orthogonal frequency-division multiplexing (OFDM) signal. The simulation and experimental results show that the SNR of the OFDM system with narrower band profiles is more susceptible to sampling clock jitter than systems with relatively wider band profiles. Further, for systems with a comparable bandwidth, HSDPA outperforms WiMAX, for example, a 5 dB error vector magnitude improvement at 15 picoseconds time jitter for a bandwidth of WiMAX 3.5 MHz profile.