Bandwidth is known as the first indicator of oscillators and the most valuable indicator of oscillators. The division of the oscillator market is often based on bandwidth, which engineers must first determine when selecting oscillators. In the course of sales, there are also many stories about bandwidth。
The bandwidth commonly referred to does not specifically indicate the bandwidth of an indicator waver to simulate the front end amplifier, which is commonly referred to as the 3db cut-off frequency point. In addition, there is the concept of digital bandwidth, which triggers bandwidth。
We often say that digital oscillators have five main functions, namely, capture, observation, measurement, analysis and archiving (d)I'm sorry. The rationale for the five functions is illustrated in figure 1。
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Figure 1, logical framework for digital oscillators
The capture component consists mainly of three chips and one circuit, i. E. Amplifier chips, a/d chips, memory chips and trigger circuits, the rationale of which is illustrated in figure 2 below. The detected signals are first converted to the voltage range that adc can receive through the probe and amplifier and integration, sampling and maintenance of circuits divides the signals into an independent sample level at a fixed sampling rate, and adc converts these electrons into digital sampling points, which are stored in the collectors for display and measurement analysis processing。
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Figure 2, figure 2
The typical circuits for oscilloscope amplifiers are shown in figure 3. This circuit is widely available in analogue circuit textbooks. This amplifier can have the equivalent of a rc low-through filter as shown in figure 4. The equivalent circuits thus extrapolate the relationship between the output voltage and the input voltage, resulting in the desired bandwidth properties, as shown in figure 5。
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Figure 3, typical circuits for amplifiers
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Figure 4, equivalent circuit model for amplifiers
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Figure 5. The ideal port chart for amplifiers
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So, we know that bandwidth f2, the output voltage, is down to 70. 7% of input voltage. Based on the equivalent model of amplifiers, we can further extrapolate the timing of the rise of the waver and the pattern of bandwidth, i. E. The relationship of 0. 35, which we often refer to: the time of rise = 0. 35 bandwidth, as shown in figure 6 below. It should be noted that 0. 35 is a theoretical value based on the goss response, which is often in the range of 0. 35-0. 45 in the actual measurement system. The "time of rise" indicator is indicated on the datasheet of the oscillator. There is a relationship between the increase time measured by the oscilloscope and the real increase time. In fast-track signal testing, the relationship is needed to correct the timing of the rise of the actually detected signal。
Measured riskime(t)2 = (tr signature)2 + (tcope)2 + (tr probe)2
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Figure 6, timing of oscillators and bandwidth
Reference: https://www. Eepw. Com. Cn/article/201702/338182. Htm
The porter chart for the front end amplifier frequency feature is the "birth certificate" issued by the new oscillator. The oscillator needs to be calibrated annually, and the porter chart is the first data to be calibrated. The measurement of the oscilloscope porter chart is shown in figure 7. The signal source starts to gradually increase the delivery of a sine wave of a certain range from the 10-mhz frequency to the power sub-unit, which divides the input of the signal energy into two-part equals and delivers it to the oscillator and to the power meter by the same length cable. The power submeters and cables are passive and can be strictly calibrated, and the frequency characteristics of the signal source itself cannot be used as a marking instrument. They need to be measured as input band values for the oscillator by the energy measured by the power gauge. Sometimes customers are interested in the port map of the oscillator, which is assessed with a direct signal source to the oscillator, and which is not very strict when the bandwidth exceeds 1 ghz. It's a power meter that needs to be used as a calibration tool
In addition, the measurement of the porter chart will require the measurement of each step of the oscillator, which will eventually result in a confluence of all steps. The measurement of the port chart takes half a day to complete, and it is not as easy as expected. As figure 8 shows, there is a porter figure for sdba 9000, and i specifically use a large amount of data from excel to give you insight into the rigour of calibration. The vertical axis is -1db/div, with test results of 10 mv/div, 20mv/div, 50mv/div, 200mv/div, 500mv/div, 1v/div etc. Many times, our competitors draw their porter charts in 10db/div, take the results of a single slot test to the client, and compare them with the results of this -db/div, all sorts of slots stacked together, and then they tell the client that their porter charts are more flat, cleaner, and even describe them as "noise." it's kind of funny. Competing parties dared to repeat this practice, assuming that chinese engineers were undifferentiated and able to think independently, and blatantly deceiving the engineers with serious disrespect. I hope to draw your attention。
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Figure 7, measurement of oscilloscope porter chart
For a more in-depth discussion of bandwidth, we need to talk about the flatness and roll-down properties of the front end amplifier bands. One from rick
This is explained in great detail in a technical white paper。
Aye pattersons in spopes
The industry now has three band characterization curves, each representing three brands: gaussian (tek), 4th oder bessel (rickey) and maximally flat (angeren)。
