The digital sampling oscilloscope is a core tool for modern electronic debugging, and its performance depends 80% on three stages: triggering, storage, and analysis. This article condenses the most common pitfalls in the laboratory into 800 words, allowing you to get started in just 10 minutes after reading.
1、 Trigger: Change 'Capture' to 'Lock'
1. Select the type first and then adjust the parameters
Edge triggering is commonly used, but anomalies such as burrs, short pulses, and violations of establishment and maintenance must be detected using pulse width or logic triggering. First identify the abnormal form, then select the corresponding type, which can save 90% of detours.
2. Trigger the principle of proximity to the source
Use SCL as the source for measuring the I ² C clock, and don't hesitate to use the spare channel on the probe tip. The closer the source signal is, the smaller the triggering jitter, so that the waveform will not drift left and right.
3. Trigger mode "syllogism"
Unknown signal → Auto finds amplitude; Stable screen → Normal leakage prevention; Occasional event → Single sequence capture. Three step progression, neither missing anomalies nor being dazzled by screen crashes.
4. Pre trigger 10% start
80% of digital system failures have been exposed within 100ns of startup. Move the trigger point to 10% -20% to see if the setup time has been consumed.
2、 Storage: Transforming 'One Frame' into 'One Movie'
1. Sampling rate ≥ 5 x bandwidth
A 100MHz signal should have at least 500MSa/s, otherwise high-frequency components will be mixed and trigger false waveforms even if they are stable.
2. Storage depth "changing time"
Formula: t=M/fs. A 10M point @ 1GSa/s provides a continuous duration of 10ms, which is sufficient to cover a USB enumeration process. The greater the depth, the sacrificed is the scrolling refresh speed, in exchange for capturing the complete protocol in one go.
3. Segmented storage
The motor is driven by 10kHz PWM, with a duty cycle of 1% and effective information of only 1 µ s. Using 1k segments x 10k points, all switch cycles within 100 seconds can be recorded, but only occupy 10M points, saving 99% of space compared to traditional scrolling mode.
4. Automatically save three piece set
Set "trigger save": waveform → internal SSD, screenshot → USB drive, parameters → CSV. Night shift debugging will no longer lose data due to power outages.
3、 Data Analysis: From "Seeing" to "Understanding"
1. Measurement items are first "counted" and then "extreme"
Open the 100k sample statistics and check the σ value; Set the limit template to ± 3 σ again, and the next run will automatically determine PASS/FAIL, which is a hundred times more efficient than aligning grid by grid with the naked eye.
2. Choose one of three FFT window functions
Hanning is used for periodic signals, Rectangular for burst signals, and Flat Top for precise frequencies. The window is wrong, -3dB bandwidth looks like 10dB attenuation.
3. Protocol decoding "three-layer filtering"
Observe amplitude and timing at the physical layer; Check ACK/NACK at the link layer; Search for keywords at the application layer. Complete DSO in one go to avoid catching it again.
4. Subtraction is the most valuable waveform operation
By using a differential probe to measure the half bridge, subtracting the VGS of the upper tube from the VGS of the lower tube, the actual driving voltage can be directly obtained, eliminating the risk of reconstructing the floating head of the ground reference.
5. Historical replay "deconvolution"
Occasional crash during startup? Open the History mode, enter 50% amplitude as the search condition, and the oscilloscope will automatically list all suspicious pulses within 2 hours, and then superimpose them onto the same time base. The abnormal waveform will be compared with the normal waveform to locate it at a glance.