Design Of High-precision Stable Sine Wave Module For Oscilloscope Calibrator

The development of science is inseparable from the advancement of measurement technology.As the most basic scientific research instrument,the oscilloscope's performance index is directly related to the development of electronic science and its application research.As the main equipment for calibrating and testing the oscilloscope,the oscilloscope calibrator is the cornerstone for the oscilloscope to work properly.With the advent of the 5G era,electronic signals in various applications require higher frequencies and better quality,which undoubtedly puts higher demands on the oscilloscope and also requires the oscilloscope calibrator to generate higher quality calibration signals.The main content of this subject is based on the oscilloscope calibrator to study the generation of high-precision and stable sine wave signals,and provide bandwidth test and amplitude calibration for the oscilloscope.The sine wave module designed in this thesis has the characteristics of wide frequency range,high frequency stability,high power flatness and low harmonic noise.The main research contents are as follows:1.The implementation of a sine wave signal.The sine wave module designed in this thesis covers wide-band signals from 0.1Hz to 4.4GHz.By analyzing the requirements of indicators and the current development of signal generation technology,a high-low frequency segmentation scheme is proposed.The low-frequency sine wave signal is generated by direct digital frequency synthesis(DDS),and the high-frequency sine wave signal is realized by phase-locked loop(PLL)frequency synthesis.2.The amplitude adjustment of the sine wave signal.The oscilloscope calibrator requires a large dynamic range and high resolution for the amplitude adjustment of the sine wave signal.In order to achieve a wide range of precise control of signal power,signal conditioning circuits such as high-precision voltage-controlled attenuation,fixed attenuation,and power amplification are designed.To ensure the stability of the devices and the reliability of the system,the corresponding current and temperature protection circuits are designed.3.Stable design of sinusoidal signals.The oscilloscope calibrator requires strict accuracy and flatness of the sine wave signal,and it is difficult to meet the index requirements by using amplitude conditioning methods such as direct amplification and attenuation.Therefore,this thesis studies the automatic level control(ALC)technology,through the coupling,detection and integration operations to achieve negative feedback control,eliminating the amplitude error introduced by other factors in the analog path.Temperature compensation is performed to further increase the amplitude stability.4.Filter network design for sinusoidal signals.The signal introduces noise and increases the harmonic components during the synthesis and amplification process,seriously affecting the waveform quality.Due to the frequency bandwidth of the signal,the complexity of the filter network design is increased.Therefore,this thesis adopts frequency segmentation design,and designs different filtering networks for different filtering requirements in the path,and optimizes the layout and filtering structure to achieve the requirements of sine wave purity index.After many experiments,the high-precision stable sine wave module designed in this thesis can meet the oscilloscope calibration below 4.4GHz bandwidth.The frequency range is from 0.1Hz to 4.4GHz,the amplitude accuracy is up to 1%,the flatness is up to 3%,the second harmonic is <-40 dBc,the third harmonic,other harmonics and nonharmonic <-45 dBc.