Oscilloscope Response Systems and Characteristics
The response characteristics of the oscilloscope will have an effect on the waveform of the signal and change the calculation of the rise time of the signal. When Pentium 4 entered the gigahertz era, Serial ATA and PCI Express and other high-speed interfaces or buses have also surpassed Gbps one after another, choosing the appropriate probe is of course an important thing, but choosing the right oscilloscope is also an indispensable task.
Measurement waveforms from the input connector are sampled and processed to be displayed on the screen, and the data is saved at the same time. Once an inappropriate oscilloscope is selected, the waveform may be distorted. Especially when measuring waveforms of high-speed serial interfaces such as PCI Express, it is important not only to measure the sampling frequency and bandwidth, but also to be aware of the oscilloscope's response characteristics. For example, when measuring a very steep signal change, it will be different due to the difference in oscilloscope response characteristics.
The response system is divided into two main categories
Oscilloscope response characteristics refer to the "transfer characteristics" of the entire measurement system from the input connector to the screen display. Generally, they can be divided into two categories: Gaussian Response and Brick-wall Response. Brick-wall response systems are also known as Flat Response.
To distinguish or compare the difference between these two types of systems, the easiest way is to look at the "-3dB frequency characteristics" and "step (Step) waveform response" of the two basic parameters.
Commonly used analogue oscilloscopes belong to the Gaussian response system, its frequency characteristics will be in the right shoulder end of the slow decline, and step waveform input even if the steeper, but also not prone to waveform distortion, that is, does not produce step waveform momentary forward (Preshoot), waveforms after the overshoot (Overshoot), or the waveforms up and down vibration of the ringing (Ringing) and other phenomena. This is a desirable characteristic when measuring digital circuit signals with short transition times.
Analogue oscilloscopes must convert a small voltage signal of a few mV at the input into hundreds of mV through several stages of amplification circuits to ensure that it is sufficient to drive a CRT display. The frequency response characteristics of these amplifier circuits are precisely Gaussian.
When measuring the waveforms of high-speed serial interfaces, broadband digital oscilloscopes with real-time sampling are generally used, and these oscilloscopes mostly use a brick-wall response type of answering system.
Brick wall response type of response characteristics, also known as the "highest flat response", in the frequency band frequency response is extremely flat, and out of the frequency band to the turn down (Roll-Off), the signal is quite steep. With such ideal frequency characteristics, there is no attenuation of the signal amplitude in the frequency band. Beyond the band, the signal amplitude becomes zero.
