Research On Measurement Of System Frequency Characteristics Based On Periodic Narrow Pulse

Frequency response measurement is very important for the analysis and design of electronic systems.So an approach based on impulse response,for system frequency characteristics testing using periodic narrow pulse as input,is proposed in this work.There are some instruments for measuring system frequency characteristics,such as frequency sweeper and network analyzer in which the sweeping frequency signal applied to the system is generally provided by direct digital synthesizer(DDS)technology and then the amplitude of the system output is detected with a peak detector(high-speed comparators and high-speed ADC)to form the amplitude frequency characteristic;Meanwhile phase frequency characteristic is obtained by phase detection circuit.The measurement method has advantages of wide range,high accuracy and mature technology;but some disadvantages are of low sweeping speed due to the limited system response,and large scale.The resulting instruments are of generally complex structure and high price.To solve problems above,the impulse response theory is deeply studied and the feasibility of periodic narrow pulse as exciting signal for frequency characteristics measurement is analyzed;Secondly,the reconfigurable phase-locked loop in FPGA is successfully controlled in high precision,so as to produce periodic short pulses with nanosecond pulse width used for measurement;Thirdly,the periodic narrow pulse signal is applied into a system under test and the system output is sampled with an analog to digital converter;Finally,the data obtained are processed with fast Fourier transform to get the frequency characteristics of the system.The experimental results show that a periodic narrow pulse signal with rich frequency components can be used to simulate impulse signal in system frequency characteristics measurement,but its measuring accuracy should be further improved;And the lower the repetition frequency of periodic narrow pulse signal is,the higher the frequency resolution is;The narrower the pulse width of the periodic narrow pulse signal is,the higher the measurement accuracy is.The proposed method has practical significance and value because of simple hardware,low cost,fast speed and adjustable accuracy within a certain range.