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Modern DSO (Digital Storage Oscilloscope)
Horizontal Trace
Horizontal Trace
Let’s apply a time-varying voltage 𝑣^ℎ(𝑡) only to the horizontal deflection plates.
It would be useful to choose a waveform that sweeps the beam uniformly from left to right, then returns the beam to the left-hand side of the screen abruptly for the next sweep.
–> This way the beam moves proportional to time.
The horizontal waveform is created by the sweep generator, the “clock” of the oscilloscope.
By controlling the period 𝑇 of the sawtooth (the timebase), we control how much time is “shown” by the scope.
The sweep generator can be triggered by various events
Vertical Trace
Vertical Trace
Let’s apply a time-varying voltage 𝑣^𝑣(𝑡) only to the vertical deflection plates.
The beam deflection is proportional to the signal applied.
We can scale the deflection using a vertical deflection amplifier to make our waveform fill the screen (for more accurate measurements).
Together (Vertical + Horizontal)
Together (Vertical + Horizontal)
Driving the horizontal plates with the sweep generator and the vertical plates with the test signal, we can now plot the test signal versus time.
Visual measurement example:
– Timebase: 1 𝜇s/div
– Vertical deflection: 50 mV/div
The sine wave has a period of 10 𝜇s (𝑓 = 100 kHz) and is 300 mVpp in amplitude
Waveform Display basics: Sampling & Bandwidth
Waveform Display basics: Sampling & Bandwidth
General sampling process:
An analog-to-digital converter (ADC) samples and converts the voltage waveform into a series of digital numbers processed by a computer.
ADC bit resolution determines quantization level, e.g. 8 bits divides the input into 2^8 = 256 quantization bins.
All samples are taken on a single trigger event.
Sampling frequency must be chosen orrectly to avoid aliasing and for the bandwidth of the anticipated signal.
Sampling Concepts:
Nyquist’s sampling theorem requires that the sample rate is atleast twice the highest frequency of the input signal: f𝑠 > 2𝑓max
This is to avoid aliasing of our original signal.
𝑓𝑠 is called the Nyquist sampling frequency.
The sample rate of the EDU1052G is 1 GSa/s (1 billion samples/sec).
Oscillscope Bandwidth:
Defines the highest frequency component that the oscilloscope can capture.
Any signals higher than the scope BW will not be accurately shown, if at all.
We can sample at rates far exceeding the bandwidth (to get lots of samples) but this does not improve the bandwidth of the scope.
100 MHz Clock Signal (same sample rate, higher BW = more detailed)
Triggering
Triggering
Purpose:
triggering = synchronized photo taking
Our waveform “picture” consists of many consecutive sample points forming the test waveform.
We must synchronize taking the photo to a point on the waveform that repeats.
Easy choice: a rising or falling edge in the test waveform at a specific voltage level.
2. Default Triggering:
The default trigger location (𝑡 = 0) on DSOs is the (horizontal) centre of the screen.
–> On older CROs, it was on the left side.
Example:
– Trigger level @ 0.0 V
– Trigger on a rising edge of the waveform
We successfully “photograph” our sinusoid with the positive-going zero crossing at time zero.
3. Triggering Mode:
Auto / Normal
In the Auto trigger mode (default), if the specified trigger conditions are not found, triggers are forced and acquisitions are made so that the signal is displayed.
In the Normal trigger mode, triggers and acquisitions occur only when the specified trigger conditions are found.
– If your trigger is not set properly, the screen will be blank with “Trig’d?”
Single / Continuous
A single trigger initiates one sweep and holds the waveform on the screen.
A continuous trigger plots successive acquisitions on top of each other, allowing you to see the evolution of the signal at various time instants.
Potential Condition Solutions
Potential Condition Solutions
Mis-Configured Trigger in Auto Mode:
-> useless output 🚨:
If we set the trigger level outside the range of voltages the input has, we fail to meet the conditions for triggering.
Auto trigger mode will initiate acquisitions at random time intervals.
-> solution💡:
proper scaling the test waveform
Adjust V/div knob until waveform fills most of the screen vertically (to maximize vertical resolution).
Adjust s/div knob so only a few cycles are displayer horizontally (for better horizontal resolution).
Adjust the Trigger Level knob until level set near middle of waveform vertically.
auto-scale lololololol
2. DC Offset of test signal:
-> useless output 🚨:
Waveform gets clipped and can’t be properly measured
reduce vertical scale will loss resolution (eg. 256 quantization levels spread across 30v, but signal only occupies about 20% of the spread)
-> solutions 💡:
Use vertical Position knob to centre the waveform
if still happen use Channel Coupling!
Changing the channel coupling to AC suppresses the DC component (offset) using a blocking capacitor on the input.
This allows you to use the greater sensitivity to display the AC component of the signal.
Basically, DC coupling is only useful for AC signals with verys mall DC offsets, or if I want to measure the DC component of the signal by noting its distance from the ground symbol.
Multi-channel Measurement
Multi-channel Measurement
Mixed-Signal Oscilloscopes (MSO)
Mixed-Signal Oscilloscopes (MSO)
MSOs measured analog and digital signals, plotting them all together.
Example: MSO-X 3104T has 4 analog channels, 16 digital channels
Generally have very high sample rates for capturing high-speed signals (e.g. 1 GHz / 5 GSa/s)
Generally loaded with software to analyze waveforms for serial protocols: I2C, SPI, UART, CAN, etc.
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