Duration of ascent and bandwidth of the ondoscope probe
Most master three pieces of limitation of ondoscope are: Degree of sensitivity insufficient and permissible range of input voltage too little and the bandwidth is limited.
Except in very high special occasion of the signal sensibility requirement, usually all of us can guarantee the level of minimum signal sensibility that the signal level is higher than the general ondoscope: The maximum level of the high level digital signal is smaller than 5V, this is within the measurement limits of peak voltage of most ondoscopes too. In view of this, the most severe restriction is the bandwidth.
Undoubtedly, the probe of the ondoscope of the wealth is the same, the vertical amplifier of the ondoscope has a bandwidth rate too. What meaning is this number value Few engineers will measure digital signal of 200MHZ with ondoscope of 100MHZ, how but measure the signal of 99MHZ with it What is the accurate meaning with width on earth How does it exert an influence on the digital signal
Fig. 3.1 has provided some clues for us. Two waveforms in the picture are to observe the result that the same signal sees by two ondoscope probes that bandwidth differs greatly. Rise quickly waveform on it is above,but under slow much. What the waveform recorded above is used is the probe quickly of duration of ascent, and following waveform, it was the probe of 6MHZ bandwidth that used. Probe of this 6MHZ bandwidth. Original document use for, filter noise, have very high input impedance at the same time, in here being mainly difference at being for outstanding the intersection of signal passing and different probes. The probe lower in bandwidth makes to export the signal ambiguity, make its rising edge and negative edge all slower. Explain with term of SIGPROC signal processing, the probe that it is the low bandwidth strains except the high frequency commponent of the measured signal.
For afford to reveal, it is the input signal respectively, probe and vertical amplifier, the rising edge of an ideal signal is extremely narrow in Fig. 3.2, input into the parts at all levels separately, so that we can see the distortion intensity when signals are during the course of systems are different to passing. Probe and vertical amplifier have same influence on signal; Slow down the duration of ascent of the signal.
Intensity of each process stage deterioration of quantization separately of Fig. 3.2.
When a probe and vertical amplifier of actual signal passing make up the system, square root that the duration of ascent when is got is equal to the sum of square of duration of ascent of each part.
So long as processing procedure cascade connected way, should each duration of ascent the square of totalizing. In this example, the appropriate duration of ascent value should fetch 10~90% duration of ascent.
It is 3DB bandwidth of probe and vertical amplifier that production firm usually adopts the ondoscope, namely F3DB, but not its duration of ascent. 3DB bandwidth and conversion relation for 10~90% duration of ascent are like being shown as follows, can also see the association that this approximate value supposed the frequency response of the probe is random electric-wave filter that the limit of several pieces of frequency is close to each other, it is gauss type.
Will refer to RMS bandwidth in index for producing manufacturer of this ondoscope, are also called the equivalent noise bandwidth FRMS, its transforming type can also see as followsing type:
We will use the probe bought from market sometimes, analyze its simple low-pass filter characteristic at this moment, these electric-wave filters do not have one gauss of frequency response curves. In this case, there are the following relations in the time constants of 10~90% of the duration of ascent and electric-wave filters of the circuit:
