Tian Shulin

A Research of High-speed Arbitrary Waveform Synthesis

Recently the primary method in arbitrary waveform synthesis is to use RAM as the data lookup table of DDS. This paper aims at bottleneck problem of the speed of RAM in arbitrary waveform synthesis, proposed a new way about highspeed arbitrary waveform synthesis by which arbitrary waveform data synthesis is achieved with a sampling speed of 500 MSa/s. Finally, this paper presents the simulation result of 500 MSa/s high-speed arbitrary wave synthesis.

Algorithm based on TDC to estimate and calibrate delay between channels of high-speed data acquisition system

As the modern electronic system becomes more complicated, the new situations and works require a data acquisition system with a more accurate time parameter. Time delay between channels of high-speed data acquisition system is an important time parameter to estimate and adjust. In high-speed data acquisition system, the ADC data output time is not fixed, and may lead to the delay time of each acquisition channel generated. In order to solve this problem, an algorithm based on TDC is proposed to estimate and calibrate the delay. The algorithm is based on the truth that the sampled data and the data synchronized clock of ADC are synchronized. So phase relationship of the data synchronized clocks can represent the delay between channels. Time-stretched Time-Digital-Converter (TDC) is used to measure the phase difference of the data synchronized clocks. The experiment result proves that the algorithm is faster than four-parameter sine wave fitting, and has a high accuracy up to 100ps.

Real-time wideband DDC based on parallel architecture in synthetic instrument

Restricted by the processing speed of device, bandwidth and filter performance of Wideband Digital IF Process are hard to achieve a breakthrough. In this paper, to solving the problems during wideband digital IF process, a parallel processing architecture is presented to efficiently lower the sample rate and process cost through multiple channels of parallel process. This paper deduces the digital down conversion technique principle, analyzes output phase difference of multiple Numerical Control Oscillator s (NCO) output and error factor for reducing SNR, and provides the index distribution basis for the specific engineering design. Finally, the correctness is verified by the experimental platform.

Analysis and implementation of data synchronization in time-interleaved ADCs system

Time-interleaved parallel technology is still the best way to implement a data acquisition system with higher sampling rate. In order to make a system of multiple analog to digital converters (ADCs) achieve an optimal performance, a large number of calibration works should be done on the parameters, such as gain, offset and time error, based on sampled data after ADCs. And it also should get correctly data sequence to store the sampled data and then to do correspondingly post-processing. However, along with the increase of sampling rate, a random reset operation of multiple ADCs system will lead to the uncertainty of data synchronous transmission and the incorrect of sampled data sequence that caused its incorrect digital post-processing. Based on an example of dual-ADC time-interleaved parallel sampling system, this paper analyzes the basic timing of sample data transmission process, and presents a calibration method of data synchronous recognition. And the guiding principles of practical engineering design are also proposed. Finally, these are tested on 20GSa/s high-speed acquisition system composed of four 5GSa/s ADCs. The results indicate that the calibration method of data synchronization and the guiding principles of practical engineering design are effective and reliable, and provide a strong support for structure of more complex high-speed time-interleaved ADCs system.

Algorithm of improving vertical resolution of digital storage oscilloscope

Vertical resolution is a significant indicator of digital storage oscilloscope (DSO) and the key to improving it is to increase digitalizing bits and lower noise. Averaging is a common digital processing method to improve signal to noise ratio (SNR) and the effective number of bits (ENOB). However, its effect is sometimes limited by the gross error in quantization and the nonperiodic of signal. An information entropy-based data fusion and average-based decimation filtering algorithm is proposed in this paper to improve the resolution of oscilloscope. For either periodic or nonperiodic signal, resolution is improved through eliminating gross error in quantization by data fusion utilizing the maximum entropy of sample data, and with further noise filtering via average-based decimation under the premise of oversampling. No subjective assumptions and constraints are added to the signal in the whole process, and without any impact on the analog bandwidth of oscilloscope under actual sampling rate.

Design for digital oscilloscopes with seamless measurement capability

Modern complicated signal tests have very high requirements for the sampling and capturing performance of oscilloscopes, but the signal capturing performance of digital oscilloscopes greatly lags behind their sampling performance, appearing as low waveform capture rate and large measuring gap, which seriously inhibits the improvement of measurement capability and efficiency of oscilloscopes. In order to maximize the waveform capture rate and eliminate the measuring gap of oscilloscopes thoroughly, this article provides a design for digital oscilloscopes with seamless measurement capability, aiming at satisfying the requirements for seamless acquisition storage, seamless data processing and seamless image display for realizing the seamless measurement of the complete set by improving the structure and optimizing the processing mechanism of oscilloscopes.

Study on signal conditioning technology in 2GHz broadband digital oscilloscope

Its the trend of electronic development to test the broadband signal. The channels of frond-end broadband signal conditioning constitute the key for the high-speed digital oscilloscope, in other words, the performance of such conditioning channels will determine the signal acquisition capacity of digital oscilloscope. In combination with the specific signal conditioning requirements, the paper describes the design of functional circuit for the high-speed digital oscilloscope, which includes broadband impedance transfer circuit, variable gain circuit, high-speed parallel drive circuit and high-speed trigger circuit. The major technologies of broadband signal conditioning is further analyzed. In view of the experience of practical system commissioning, the DC-2GHz broadband signal conditioning test is feasible. The design could be suggested to use in other broadband instruments.

Fault diagnosis of analog circuits based on phasor circle model

Algorithm of phasor circle model, a fault modeling on complex plane for fault dictionary in time domain analysis of linear analog circuit, is presents. The proposed algorithm achieved to characterize all potential fault status of each component with a circle on complex plane, using a voltage measurement approach on the only output node, and the unified mathematical formula of all complex circle is also presented with the parameters of center coordinate and radius. Furthermore, an approach of design for testability is discussed to minimize the ambiguous group. This algorithm can be used for identifying both soft fault and hard fault. Finally, an example circuit is presented to verify the efficient of the proposed algorithm.

Research on fast measurement method for active element pattern of phased array antenna

A novel fast measurement approach in the phase-shift measurement method to obtain the active element pattern in phased array antenna is investigated in this paper. The active element pattern is not only used in the process of solving each channel excitation, but also needed in the recovery of whole pattern. Since the accuracy of active element pattern will directly affects the precision of fast measurement results, it is more important to determine the active element pattern accurately compared with other measurement methods. In this paper, the elements in the phased array antenna are composed of half-wave dipoles, and a novel determination method of active element pattern which achieves accurate pattern calculations with less computer memory and computation time is introduced. The calculating formulas are presented, and the correctness along with the feasibility of this proposed method is verified and illustrated through experimental simulation.

Optimal design of adjustable frequency response linear-phase filters

A digital linear-phase finite-length impulse response (FIR) filter design method is proposed, which has adjustable frequency response. For this purpose, Farrow structure is employed in which the overall transfer function is a weighted linear combination of fixed subfilters and where the weights are directly determined by the input parameter. Optimal design technique is introduced which generates globally optimal overall filters in the Chebyshev sense over a whole set of filter specifications. An example is included in the paper to demonstrate the effectiveness.