Basic principle and measuring method of oscilloscope
Oscilloscope is one kind of electrical measurement equipment with wide application. It could transfer invisible electrical signal to visible image to facilitate people research change processes of all kinds of electricity phenomenon. Oscilloscope use narrow electron beam which consists high-speed electronics and project onto screen coated with fluorescent substance to produce small spot (this is original working principle of analog oscilloscopes. Under the function of measured signal, electronics like the point of a pen which could on screen describe change curve of measured signal during instantaneous value. An oscilloscope can be used to observe the waveform curves of various signal amplitudes varying with time. It could also be used to measure various electricity, such as voltage, current, frequency, phase, amplitude modulation and etc.
(1) pre-adjusting: counterclockwise rotate the brightness button to the bottom, shift vertical and horizontal positions to the middle, set the attenuation gear at the highest level, place scan “outside X gear”
(2) turn on the power, do following steps waiting for one or two minutes after the indicator light is on
(3) adjust luminance first, then adjust the focus, adjust vertical and horizontal displacement to make the light point in center of suitable area.
(4) adjust scan, scan fine tuning and X gain, observe scan.
(5) adjust outside X gear to suitable scan range, observe the voltage waveform according to sine and cosines law on vertical direction inside the device.
(6) Connect the applied voltage to be studied to oscilloscope through Y input and earth. Adjust all gears to suitable position and observe waveform (the picture changes with time) (the synchronous polarity switch can make the starting point of the image start from positive half cycle or negative half cycle.)
(7) If you want to observe the vertical migration of light spot (with one added DC voltage), could adjust scan to “outside X gear”.
In general, the frequency of the calibration signal is 1kHz and the amplitude is 0.5v, which is used to calibrate the internal scanning oscillator frequency of the oscilloscope. If it is abnormal, the corresponding potentiometer of the oscilloscope (internal) should be adjusted until it is consistent.
For the analog front end, main performance index of oscilloscope
The simulation bandwidth, including the amplitude-frequency response characteristics to the measured signal, is presented as the rise time index and the overshoot performance index in the time domain;
Dynamic range of input signal amplitude (range from minimum vertical sensitivity to maximum vertical sensitivity for non-digital processing);
Initial error characteristics and temperature drift characteristics of dc gain accuracy and offset accuracy;
Input impedance characteristics (parasitic capacitance of resistance in parallel) affect the effect on the circuit under test with or without a probe.
High precision dither test of digital oscilloscope
Jitter can be described as the periodic change of edge period or phase of adjacent pulse edge or even non-adjacent pulse edge. These indicators are suitable for measuring long-term and short-term clock and data stability.The data transmission performance of complex system is predicted by analyzing the jitter index and using the jitter test results.
Periodic jitter is used to measure edge - to - edge timing of clock or data cycle samples. For example, by measuring the time between the rising edges of 1,000 clock cycles, you can sample the statistical cycles that will tell you the quality of the signal.The standard deviation becomes RMS periodic jitter, the maximum period minus the minimum period, to get peak to peak period jitter.The precision of each measurement period determines the precision of jitter measurement.
Phase jitter is used to measure the time deviation between the edge of the measured signal and the edge of a reference signal so that any change in the signal phase can be detected.This indicator is different from periodic measurement in many ways. First, it USES each edge alone, without saying "period" or "cycle."Second, it can measure large time shifts.The edge phase can be deviated by hundreds or thousands of degrees, but can still be measured with very high precision (360 degrees equals one cycle or cycle time). The commonly used measure of phase error is the time interval error (TIE), and the measurement results are expressed in seconds relative to degrees.TIE matches the signal edges to the reference edges, and sums up the differences between the edges.After comparing a large number of edges, a sample set can be provided for analysis.As with the above periodic measurements, the standard deviation becomes RMS TIE, the maximum time minus the minimum time to get peak to peak TIE and so on.