Several Factors Affecting Oscilloscope Testing

　　Factors Affecting Oscilloscope Testing

　　There are no indicators of flat response and Gaussian response in the specifications of oscilloscopes. Similar comparisons or discussions may appear in oscilloscopes for the following reasons:

　　As we all know, oscilloscopes are time-domain instruments. Since Tektronix invented the first triggerable analog oscilloscope, the bandwidth of an oscilloscope has always been the most important indicator. It refers to the analog bandwidth of the preamplifier inside the oscilloscope. However, the definition of oscilloscope bandwidth is in the frequency domain, that is, the frequency point when the sine wave amplitude decays to the -3dB point. A complex high-speed signal contains a wealth of spectral components. If you need to accurately measure the signal, you must know the amplitude and phase of each of their spectral components, so the amplitude-frequency characteristic and phase-frequency characteristic of the oscilloscope are very important.

　　From the development in recent years, the bandwidth of digital oscilloscopes is getting higher and higher. From the TDS7000 4GHZ bandwidth oscilloscope launched by Tektronix in 2000, the TDS6000 6GHZ bandwidth oscilloscope launched in 2001, the TDS7704B 7GHZ bandwidth oscilloscope launched in 2003, to the recent TDS6804B 8GHZ bandwidth oscilloscope, the bandwidth has been increasing almost every year. When the bandwidth of the oscilloscope reaches several GHZ, it is increasingly difficult for the preamplifier as an analog device to ensure good amplitude-frequency and phase-frequency characteristics. Tektronix is ​​the only company that has mastered this most critical technology. Some manufacturers cannot do this, so they have to use other methods to remedy the lack of bandwidth of analog devices and obtain higher bandwidth, and the frequency response curve will naturally change.

　　As more and more high-speed signals are being generated and the signal rates are getting faster, new requirements are being put forward for real-time oscilloscopes. Oscilloscope manufacturers have also seen some new technologies in their digital oscilloscopes. The most notable one is that oscilloscopes use digital signal processing technology (DSP) to achieve better performance. The main applications of DSP in digital oscilloscopes include:

　　Enhanced bandwidth

　　Faster rise time

　　Gain and waveform calibration and improvement

　　Amplitude and phase improvements

　　Optical Reference Receiver Normalization

　　Among them, the third generation oscilloscope (DPO) of Tektronix is ​​the best embodiment of DSP technology. Reasonable use of DSP can improve the signal fidelity of oscilloscope testing.

　　However, the use of DSP technology will confuse every oscilloscope user, especially in the following questions: "Can bandwidth be improved through DSP?", "The bandwidth of the oscilloscope is analog bandwidth, what is the relationship with DSP technology?", "Is the current oscilloscope bandwidth analog bandwidth or DSP bandwidth?", "What are the negative effects of DSP technology?"

　　The analog bandwidth of Tektronix's latest TDS6804B 8GHZ bandwidth oscilloscope is 7GHZ, and the bandwidth after DSP enhancement is 8GHZ. In order to ensure that every tester understands these two methods, the DSP bandwidth enhancement function can be turned on and off in TDS6804B. Tektronix tells every tester the advantages and problems brought by DSP enhanced bandwidth, helping them understand the test results of analog bandwidth and DSP enhanced bandwidth, and better perform high-speed signal testing.