Study of ultra-wideband radar signals-generated technology using two-channel signal generator

Synthesis of ultra-wideband （UWB） linear frequency modulation radar signals is a very important technology for microwave imaging, target identification and detection of low radar-cross-section （RCS） targets. A new method of UWB radar signals generation with two-channel signal generator is presented. The realization structure is given; the principle and errors of signal synthesis are analyzed. At the same time, an automatic .adjustment measure of signal phase is proposed because of phase discontinuity of waveform in this method. The simulation experiment and analysis results indicate that radar signals with large instantaneous bandwidth can be generated by means of this method on the condition that the high-speed digital devices are limited.

Digital Predistortion and Measurement Method

Digital PreDistortion(DPD)is a very useful method to improve the linearity of Power Amplifiers(PAs)for LTE and upcoming 5 G networks.As the spectrum resources are becoming more and more crowded,and the communications bandwidth are broader,the ACPR(Adjacent Channel Leakage Ratio)is very important to communication systems.DPD is one of the useful means for PA to reduce ACPR.This article demonstrates what DPD is and how DPD is achieved,the measurement of the Digital Distortion of a PA using a vector generator and vector analyzer,and the measurement results has been discussed.

Design and implementation of the NaI(Tl)/CsI(Na) detectors output signal generator

We designed and implemented a signal generator that can simulate the output of the NaI（Tl）/CsI（Na）detectors＇pre-amplifier onboard the Hard X-ray Modulation Telescope（HXMT）.Using the development of the FPGA（Field Programmable Gate Array）with VHDL language and adding a random constituent,we have finally produced the double exponential random pulse signal generator.The statistical distribution of the signal amplitude is programmable.The occurrence time intervals of the adjacent signals contain negative exponential distribution statistically.

Millimeter-wave modulated optical pulse generated by pulse repetition rate multiplication and temporal Talbot effect

A novel scheme was proposed to generate a millimeter-wave （MMW） optical pulse by combining pulse repetition rate multiplication （PRRM） technology and temporal Talbot effect （TTE）. A cascaded Mach- Zehnder interferometer （MZI） lattice was used for PRRM, and a linearly chirped fiber grating （LCFG） was used as TTE. The basic principle was analyzed by using a Gaussian input short pulse and its characteristics were discussed by numerical simulation. It is shown that the proposed scheme is feasible for MMW signal generation and has potential merits for practical application of radio over fiber （ROF） technology.

4 GHz bit-stream adder based on ∑△ modulation

The conventional circuit model of a bit-stream adder based on sigma delta（∑Δ） modulation is improved with pipeline technology to make it work correctly at high frequencies.The integrated circuit（IC） of the bit-stream adder is designed with the source coupled logic structure and designed at the transistor level to increase the operating frequency.The IC is fabricated in TSMC＇s 0.18-μm CMOS process.The chip area is 475×570μm^2.A fully digital∑Δsignal generator is designed with a field programmable gate array to test the chip.Experimental results show that the chip meets the function and performance demand of the design,and the chip can work at a frequency of higher than 4 GHz.The noise performance of the adder is analyzed and compared with both theory and experimental results.

A New Full Bridge High Intensity Focused Ultrasound Power System with Harmonic Cancellation

The feasibility of a new full bridge high intensity focused ultrasound(HIFU) amplifier system with harmonic cancellation is evaluated in this study. Harmonic cancellation technique is applied to these power amplifiers, which can eliminate the 3rd harmonic and all even harmonics. Since this technique requires two channels of phase signal to control one channel of power amplifier, the signal generator is required to double its output. The transducer array proposed in this study has 100 elements. So we choose an FPGA chip to generate 200 driving signals, and each channel has a phase resolution of 2ns, less than 1°. The phase signal from the FPGA meets the requirement of driving the power amplifiers. The output waveform of one channel of power amplifier(voltage across the transducer) is evaluated, and shows fewer harmonic components.