Measurement Bench • Accessories • Power supply • Wave form generator • Multimetre • Oscilloscope Dr. L.Scucchia OSCILLOSCOPE Dr. L.Scucchia Oscilloscope (1) The oscilloscope allows to display a voltage (vertical axis - Y axis) versus time (horizontal axis - X axis). The oscilloscope can also display two voltages on both the axes (XY mode). The quantities shown on the screen are voltages. To facilitate reading of the magnitudes, on the screen there is a grid consisting of some horizontal and vertical divisions. The oscilloscopes in the laboratory are DSO3202A and MSO-X 3012T by Keysight (ex Agilent). DSO stands for Digital Storage Oscilloscope MSO stands for Mixed Signal Oscilloscope Both oscilloscopes use an analog-to-digital converter (ADC) to convert the measured voltage into digital information. The digitized data are stored in a “channel memory” Dr. L.Scucchia Oscilloscope (2) Attenuator Input BNC + Amplifier - DC Offset Trigger Coupling + DC Trigger Level Channel Memory ADC Trigger signal Trigger Comp - Yellow = Channel specific blocks Blue = System blocks DSO Block Diagram Display DSP Timebase System Trigger Logic CPU System Dr. L.Scucchia Oscilloscope (3) A probe feeds the input signal into the oscilloscope where the attenuator and the amplifier are used to compensate for input levels for various voltage per division settings. The trace position is adjusted changing the DC Offset. Attenuator Input BNC + Amplifier - DC Offset Trigger Coupling + DC Trigger Level Channel Memory ADC Trigger signal Trigger Comp - Yellow = Channel specific blocks Blue = System blocks DSO Block Diagram Display DSP Timebase System Trigger Logic CPU System Dr. L.Scucchia Oscilloscope (4) The ADC provides a discrete form of the signal: • in the time domain (sampling) and • in the amplitude domain (quantization). The ADC converter operates continuously at the maximum sampling frequency. Attenuator Input BNC + Amplifier - DC Offset Trigger Coupling + DC Trigger Level Channel Memory ADC Trigger signal Trigger Comp - Yellow = Channel specific blocks Blue = System blocks DSO Block Diagram Display DSP Timebase System Trigger Logic CPU System Dr. L.Scucchia Oscilloscope (5) The memory is organized as a circular buffer. The write pointer advances at the rate of the ADC. Attenuator Input BNC + Amplifier DC Offset Trigger Coupling + DC Trigger Level Channel Memory ADC - Trigger signal Trigger Comp - Yellow = Channel specific blocks Blue = System blocks DSO Block Diagram write pointer Display DSP Timebase System Trigger Logic CPU System Dr. L.Scucchia Oscilloscope (6) The trigger signal, through the timebase system, causes the start of the reading cycle of the channel memory Attenuator Input BNC + Amplifier DC Offset Trigger Coupling + DC Trigger Level Channel Memory ADC - Trigger signal Trigger Comp - Yellow = Channel specific blocks Blue = System blocks DSO Block Diagram write pointer read pointer Display DSP Timebase System Trigger Logic CPU System Dr. L.Scucchia Oscilloscope (7) The trigger event defines a reading interval. The trigger determines when captured data are stored and displayed. On the display the result is a signal portion preceding and following the trigger event read pointer Trigger level 0 k n-1 Dr. L.Scucchia Oscilloscope (8) Trigger problems (different trigger events) read pointers Two or more trace on the display. A trace in movement on the display Trigger level 0 0 0 k k n-1 n-1 k n-1 Dr. L.Scucchia Oscilloscope (9) Newer DSOs use custom DSPs to quickly process data and then send waveform data into display memory. Attenuator Input BNC + Amplifier - DC Offset Trigger Coupling + DC Trigger Level Channel Memory ADC Trigger signal Trigger Comp - Yellow = Channel specific blocks Blue = System blocks DSO Block Diagram Display DSP Timebase System Trigger Logic CPU System Dr. L.Scucchia • • • • • Sample Rate Oscilloscope Bandwidth Rise Time Memory Depth Actual Sample Rate Dr. L.Scucchia Oscilloscope (10) Sampling Theory The Nyquist sampling theorem states that for a limited bandwidth signal with maximum frequency fMAX, in order to reconstruct the sampled signal without aliasing, sampling frequency fS must satisfy this equation: fMAX fS /2 Nyquist frequency (fN ) Aliasing Aliasing occurs when signals are under-sampled (fMAX>fS/2). Aliasing is the signal distortion caused by low frequencies falsely reconstructed from an insufficient number of sample points. Dr. L.Scucchia Oscilloscope (11) Oscilloscope Bandwidth and Sample Rate (1) For the sampling theory the banwidth should be fBW =fS/2 assuming there are no frequency components above fMAX (fBW) and it requires a system with an ideal brick-wall frequency response. Attenuation 0 dB fBW= fs/2 Frequency Dr. L.Scucchia Oscilloscope (12) Oscilloscope Bandwidth and Sample Rate (2) • All oscilloscopes exhibit a low-pass frequency response – typically called a Gaussian response. • A Gaussian frequency response closely approximates a single-pole low-pass filter. As the frequency of an input signal increases, the Oscilloscope will begin to attenuate the input signal and then begin to make inaccurate measurements. • The frequency at which a sine wave input signal is attenuated by -3 dB is the oscilloscope bandwidth. But -3 dB attenuation is about -30% attenuation (considering the formula 20 Log(Vo/Vi)) . Dr. L.Scucchia Oscilloscope (13) Oscilloscope Bandwidth and Sample Rate (3) On the other hand, • digital signals have frequency components above the fundamental frequency (square waves are made up of sine waves at the fundamental frequency and an infinite number of odd harmonics), and • typically oscilloscopes (with 500MHz bandwidths and below) have a Gaussian frequency response. So, in practice, the oscilloscope bandwidth should be equal or less than a fourth of sampling frequency: fBW ≤ fS/4. This way, there is less aliasing, and aliased frequency components have a greater amount of attenuation. fBW≤ fs/4 Frequency Dr. L.Scucchia Oscilloscope (14) Example: bandwidth effect This slide shows two different bandwidth oscilloscopes capturing the same 100 MHz square waveform. The first oscilloscope has fBW=fMax=100MHz The second oscilloscope has fBW=5fMax=500MHz, it is able to capture up to the fifth harmonic with minimal attenuation. Input = 100-MHz Digital Clock Response using a 100-MHz BW scope Response using a 500-MHz BW scope Dr. L.Scucchia Oscilloscope (15) Oscilloscope Rise Time It is the fastest edge speed the oscilloscope can produce and not the fastest edge speed that it can accurately measure. Closely related to an oscilloscope bandwidth specification is its rise time specification. Bandwidth Rise time Oscilloscopes with a Gaussian-type frequency response have rise time ≈ 0.35/fBW With rise time obtained from 10% to 90% of the Vtop. Dr. L.Scucchia Oscilloscope (16) Oscilloscope Bandwidth Required • The oscilloscope bandwidth required to accurately measure a signal is determined by signal rise time. • Faster edges have a spectrum with higher frequency components. • However, there is an inflection (or "knee") in the frequency spectrum of fast edges where frequency components higher than fknee are insignificant in determining the shape of the signal [1]. fknee = 0.5 / signal rise time (based on 10% - 90% thresholds) fknee = 0.4 / signal rise time (based on 20% - 80% thresholds) Required accuracy Oscilloscope band width required 20% fBW = 1.0 x fknee 10% fBW = 1.3 x fknee 3% fBW = 1.9 x fknee [1] Howard W. Johnson's ,”High-Speed Digital Design – A Handbook of Black Magic” Dr. L.Scucchia Oscilloscope (17) Memory Depth and Sample Rate o For an oscilloscope's analog-to-digital converter there is a maximum sample rate. o The memory point number (memory depth) of an oscilloscope is fixed. o The actual sample rate is determined by the time of the acquisition (related to the oscilloscope horizontal time/div scale). Actual sample rate = memory depth/ acquisition time • Storing 50μs of data in 50000 memory points, the actual sample rate is 1 GSa/s. • Storing 50ms of data in 50000 memory points, the actual sample rate is 1 MSa/s. 50 ms Sample rate = 1 MSa/s 50000 points Oscilloscope achieves the actual sample rate decimating the unneed samples. The actual sample rate is displayed in the summary box in the right-side information area. Dr. L.Scucchia Oscilloscope Sample Rate Oscilloscope Bandwidth Memory Depth Oscilloscope Bandwidth Rise Time Actual Sample Rate Dr. L.Scucchia Oscilloscope (18) DSO3202A (Agilent) 200-MHz Bandwidth 2 analog channels 1 GSa/s sample rate MSO-X 3012T (Keysigth) 100 MHz Bandwidth 2 analog +16 digital channels 5 GSa/s sample rate Dr. L.Scucchia Oscilloscope (19) Run Control Softkeys Horizontal Controls Measure controls Waveform controls Vertical controls Trigger controls Auto Scale Analog channel Inputs Compensation terminals Dr. L.Scucchia Oscilloscope DSO3202A (Agilent) Display Dr. L.Scucchia Oscilloscope (20) MSO-X 3012T (Keysight) Display Dr. L.Scucchia Oscilloscope (21) Softkeys The functions of these keys change based upon the menus shown on the display directly above the keys. MSO-X 3012T DSO3202A The Back/Up key moves up in the softkey menu hierarchy. At the top of the hierarchy, the key turns the menus off, and oscilloscope information is shown instead. Entry knob It is used to select items from menus and to change values. The function of the Entry knob changes based upon the current menu and softkey selections. The curved arrow symbol next the entry knob illuminates whenever the entry knob can be used to select a value. When the Entry knob symbol appears on a softkey, you can use the Entry knob, to select values. Often, rotating the Entry knob is enough to make a selection. Sometimes, you can push the Entry knob to enable or disable a selection. Pushing the Entry knob also makes popup menus disappear. Dr. L.Scucchia Oscilloscope (22) Low Frequency Compensation 1. Set the Probe menu attenuation to 10X. 2. Attach the probe tip to the probe compensation connector. 3. Press the Autoscale front panel button. 4. If the waveform is not rectangular you must compensate. 5. Through a nonmetallic tool adjust the screw located near the probe up to get a signal perfectly compensated. High Frequency Compensation 1. Using the BNC adapter, connect the probe to a square wave generator. 2. Set the square wave generator to a frequency of 1 MHz and an amplitudeof 1 Vp-p. 3. Press the Autoscale front panel button. 4. If the waveform does not appear like the Correctly Compensated waveform shown in figure, then adjust the 2 high frequency compensation adjustments on the probe for the flattest square wave possible. Dr. L.Scucchia Oscilloscope (23) Vertical controls DSO3202A They include: [1] and [2] analog channel on/off keys: these keys permit to switch a channel on or off, or to access a channel menu in the softkeys. There is one channel on/of for each analog channel. Vertical scale knobs: for each channel there is a knob marked with . Use these knobs to change the vertical sensitivity (gain) of each analog channel. Vertical position knobs: use these knobs to change the channel vertical position on the display. sensitivity (gain) of each analog channel. MSO-X 3012T MSO-X 3012T Mathematical operations are activated by pressing Math. The waveforms may be stored using the menu Ref. Dr. L.Scucchia Oscilloscope (24) Vertical controls: Channel menu (softkeys) It appears after pressing channel keys [1] or [2] DSO3202A • Channel Coupling Control • Bandwidth Limit Control • Probe Attenuation Control • Invert Control • Digital Filter Controls MSO-X 3012T • To specify channel coupling • To specify channel input impedance • To specify bandwidth limiting • To change the vertical scale knob's coarse/fine adjustment setting • To invert a waveform • Setting Analog Channel Probe Options Dr. L.Scucchia Oscilloscope (26) MSO-X 3012T To specify channel coupling In the Channel Menu, press the Coupling softkey to select the input channel coupling: • DC — DC coupling is useful for viewing waveforms with a not large DC offsets. • AC — AC coupling is useful for viewing waveforms with large DC offsets. AC coupling places a 10 Hz high-pass filter in series with the input waveform that removes any DC offset voltage from the waveform. When AC coupling is chosen, you cannot select 50Ω mode. This is done to prevent damage to the oscilloscope. To specify channel input impedance In the Channel Menu, press Imped (impedance); then, select either: • 50 Ohm — matches 50 ohm cables commonly used in making high frequency measurements, and 50 ohm active probes. When AC coupling is selected or excessive voltage is applied to the input, the oscilloscope automatically switches to 1M Ohm mode to prevent possible damage. • 1M Ohm— is for use with many passive probes and for general-purpose measurements. The higher impedance minimizes the loading effect of the oscilloscope on the device under test. Dr. L.Scucchia Oscilloscope (28) MSO-X 3012T To specify the probe attenuation This is set automatically if the oscilloscope can identify the connected probe. If the connected probe is not automatically identified by the oscilloscope, you can manually set the attenuation factor as follows: 1. Press the Probe softkey until you have selected how you want to specify the attenuation factor, choosing either Ratio or Decibels. 2. Turn the Entry knob to set the attenuation factor for the connected probe. • When measuring voltage values, the attenuation factor can be set from 0.1:1 to 10000:1. • When measuring current values with a current probe, the attenuation factor can be set from 10 V/A to 0.0001 V/A. • When specifying the attenuation factor in decibels, you can select values from -20 dB to 80 dB. Dr. L.Scucchia Oscilloscope (26) DSO3202A Connection control - pushing the button to the right of Coupling you can choose between three possible connections: AC for a connection via capacitor (display the AC component) DC for a direct connection (display full signal) GND for the check of the reference level (ground voltage) Bandwidth Limit Control - allows to remove, from the waveform examined, the high frequency components not relevant to the measurement made. Press the key corresponding to BW Limit function is activated (ON) and all components at frequencies greater than 20 MHz are rejected. Dr. L.Scucchia Oscilloscope (27) DSO3202A Control probe attenuation - Allows you to specify the attenuation on the probe selected. The probe attenuation control changes the attenuation factor for the probe. The attenuation factor changes the vertical scaling of the oscilloscope so that the measurement results reflect the actual voltage levels at the probe tip. Invert control - The invert control inverts the displayed waveform with respect to the ground level. Digital filter controls - Pressing the Digital Filter menu key displays the Filter Controls. The filter controls set the digital filter used to filter the sampled waveform data. The types of filters that are available are shown in the table. Dr. L.Scucchia Oscilloscope (28) Horizontal controls DSO3202A The oscilloscopes permit to fix only one value of time per division for all waveforms. • Horizontal scale knob: it is marked with the symbol and permit to adjust the time/div (sweep speed) setting. • Horizontal position knob: turn the knob marked ◄► to see through the waveform data horizontally. MSO-X 3012T The menu associated with the time base is activated by pressing: • [Main/Delayed] (DSO3202A), • [Horiz] and Zoom key (MSO-X 3012T). Dr. L.Scucchia Oscilloscope (29) Horizontal controls MSO-X 3012T • You can see the captured waveform before the trigger or after the trigger. If you pan through the waveform when the oscilloscope is stopped (not in Run mode) then you are looking at the waveform data from the last acquisition taken. • [Horiz] key: press this key to open the Horizontal Menu where you can select XY and Roll modes, enable or disable Zoom, enable or disable horizontal time/division fine adjustment, and select the trigger time reference point. • Zoom key : Press the zoom key to split the oscilloscope display into Normal and Zoom sections without opening the Horizontal Menu. • [Search] key — Lets you search for events in the acquired data. • [Navigate] keys — Press these keys to navigate through captured data via time, search events, or segmented memory acquisition. Dr. L.Scucchia Oscilloscope (30) Horizontal controls MSO-X 3012T The figure shows the Horizontal menù obtained pressing the [Horiz] key. • • • • To change the horizontal time mode (Normal, XY, or Roll) To display the zoomed time base To change the horizontal scale knob's coarse/fine adjustment setting To position the time reference (left, center, right) Dr. L.Scucchia Oscilloscope (33) Trigger controls DSO3202A Level: it changes the voltage level of the trigger signal. Force: it forces the acquisition. 50%: voltage level of the trigger signal is set equal to the average value. Ext Trig: external trigger. Mode/Coupling: Trigger menu is activated. • • • • • Mode Edge, Pulse e Video (metods) Source CH1, CH2, ext, … Slope Sweep Auto, Normal Coupling AC, DC, LFrejet e HFrejet Dr. L.Scucchia Oscilloscope (34) Trigger controls MSO-X 3012T These controls determine how the oscilloscope triggers to capture data. • • • • • • • • • • • • • • Adjusting the Trigger Level Forcing a Trigger Trigger Edge then Edge Trigger Pulse Width Trigger Pattern Trigger OR Trigger Rise/Fall Time Trigger Nth Edge Burst Trigger Runt Trigger Setup and Hold Trigger Video Trigger Serial Trigger Zone Qualified Trigger Trigger menù Dr. L.Scucchia Oscilloscope (35) Trigger controls MSO-X 3012T You can adjust the trigger level for a selected analog channel by turning the Trigger Level knob or using the touchscreen. The [Force Trigger] key causes a trigger (on anything) and displays the acquisition. The [Trigger] key displays the trigger menu: • Press the Trigger softkey, and use the Entry knob to select Edge. • Select the trigger source (Analog channel, Digital channel, External, Line, WaveGen, WaveGen Mod (FSK/FM)) • Press the Slope softkey and select: Rising, Falling, Alternating and Either edges. Dr. L.Scucchia Oscilloscopio (27) DSO3202A (Agilent) Real-time sampling In the real-time sampling mode, single waveforms are sampled at same intervals. The digitizer works at maximum speed to acquire as many points as possible in one sweep, and the 3000 Series oscilloscopes provide actual sampling rates up to 1 GSa/s the maximum sample rate. In real-time sampling the trigger event happens on a particular feature of the waveform (amplitude). In this type of data acquisition, the sample rate of the ADC determines the sample spacing and the number of points that will be displayed. Equivalent time Sampling The input signal is only sampled once per trigger. At the next triggered, a small delay is added and another sample is taken. The number of samples determines the necessary number of cycles to reproduce the waveform. Dr. L.Scucchia Oscilloscope (42) Waveform keys MSO-X 3012T [Acquire] key: lets you select Normal, Peak Detect, Averaging, or High Resolution acquisition modes and use segmented memory [Display] key: lets you access the menu where you can enable persistence, clear the display, and adjust the display grid (graticule) intensity. [Touch] key: press this key to disable/enable the touchscreen. Dr. L.Scucchia Oscilloscope (43) MSO-X 3012T To select the acquisition mode: 1 Press the [Acquire] key on the front panel. 2 In the Acquire Menu, press the Acq Mode softkey; then, turn the Entry knob to select the acquisition mode. The Infinii Vision oscilloscopes have the following acquisition modes: • Normal — at slower (greater) time/div settings, normal decimation occurs, and there is no averaging. Use this mode for most waveforms. • Peak Detect — at slower (greater) time/div settings, the maximum and minimum samples in the effective sample period are stored. Use this mode for displaying narrow pulses that occur infrequently. • Averaging —this mode permit to average multiple acquisitions together to reduce noise and increase vertical resolution (at all time/div settings). Averaging requires a stable trigger. • High Resolution — at slower time/div settings, all samples in the effective sample period are averaged and the average value is stored. Use this mode for reducing random noise. It extracts an average from sequential sample points within the same acquisition. In MSO-X 3012T model you can use only the Realtime sampling. The Equivalent time sampling option is present in MSO-X 3102T, MSO-X 3104T model. Dr. L.Scucchia Oscilloscope (41) Run Control keys • When the [Run/Stop] key is green, the oscilloscope is acquiring data (is running) when trigger conditions are met. To stop acquiring data, press [Run/Stop]. • When the [Run/Stop] key is red, data acquisition is stopped. To start acquiring data, press [Run/Stop]. • To capture and display a single acquisition (whether the oscilloscope is running or stopped), press [Single]. The [Single] key is yellow until the oscilloscope triggers. DSO3202A MSO-X 3012T Dr. L.Scucchia Oscilloscope (45) Autoscale Control MSO-X 3012T Tools keys : • [Utility] key —the utility Menu, which lets you configure the oscilloscope's I/O settings, use the file explorer, set preferences, access the service menu, and choose other options. • [Quick Action] key — Press this key to perform the selected quick action: measure all snapshot, print, save, recall, freeze display, and more. • [Wave Gen] key — Press this key to access waveform generator functions. • [Analyze] key — To access analysis features like: - Measurement threshold setting. Trigger level setting. Video trigger automatic set up and display. Counter (DVMCTR). Digital voltmeter (DVMCTR) Mask testing The DSOX3PWR power measurement and analysis application. File keys [Save/Recall] key: it is used to save or recall a waveform or setup. [Print] key: it opens the Print Configuration Menu so you can print the displayed waveforms. Dr. L.Scucchia Oscilloscope (28) Measure Controls DSO3202A Meas Cursor Sourcee: Voltage: Time Clear Display All: CH1, CH2 Vpp,Vmax, Vmin, Vavg,... Freq, Period, OFF, ON Manual: Menù Track: Menù Auto Measure: Menù Meas button on the front panel activates the automatic measurement system, in particular this enables oscilloscope to perform 20 different measures including: Vpp, Vmax, Vmin, Vamp, Vavg, Vrms, Freq, Period, risetime and Fall Time. The Cursor button on the front panel activates the menu corresponding to the measures concerning the marker. There are three modes: Manual, Track and Auto Measure. • Manual, the screen shows two parallel cursors that can be moved on the track in order to obtain the measures of voltage or of time desired. The values corresponding to the cursors are shown in the upper part of the screen. • Track, two sliders are automatically activated that can be adjusted using the added knob. • Auto Measure, available when the measurement system is automatically activated, the oscilloscope displays the cursor in relation to the latest measures Dr. L.Scucchia used. Oscilloscope (44) Measure controls MSO-X 3012T The measure controls consist of: • Cursors knob: Push this knob to select cursors from a popup menu. Then, after the popup menu closes (either by timeout or by pushing the knob again), rotate the knob to adjust the selected cursor position. • [Cursors] key: Press this key to open a menu that lets you select the cursors mode and source. • [Meas] key: Press this key to access a set of predefined measurements. Dr. L.Scucchia Oscilloscope (29) DSO3202A (Agilent) Voltage measurements: • Vpp • Vmax • Vmin • Vavg • Vamp • Vtop • Vbase • Vrms • Overshoot • Preshoot (Peak-to-Peak Voltage) (Maximum Voltage) (Minimum Voltage) (Average Voltage) (Amplitude Voltage = Vtop - Vbase) (Top Voltage) (Base Voltage) (True Root-Mean-Square Voltage) (Measure the overshoot voltage in percent (Vmax-Vtop)/Vamp. Overshoot is a waveform distortion which follows a major edge transition) (Measure the preshoot voltage in percent (Vmin-Vbase)/Vamp,. Preshoot is a waveform distortion which precedes a major edge transition) Dr. L.Scucchia Oscilloscopio (30) 3202A (Agilent) Time Measurements: • Frequency • Period • Rise Time • Fall Time • +Width • -Width • +Duty • -Duty • Delay 1→2 • Delay 1→2 Dr. L.Scucchia Oscilloscope (31) DSO3202A (Agilent) Delay 1-2, rising edges Delay 1-2, falling edges 50% Channel 1 Dta 50% t1 Channel 2 Left display side Left display side Dta t2 Delay From channel 1 to channel 2 rising edges ( t2-t1) Channel 1 50% 50% t1 Channel 2 t2 Delay From channel 1 to channel 2 Falling edges ( = t2-t1) t2-t1=Dta>0 Dr. L.Scucchia Oscilloscope (32) DSO3202A (Agilent) Left display side Delay 1-2, rising edges Channel 1 t2-t1=-Dtb<0 50% Dta 50% t2 50% Dta=T-Dtb>0 Channel 2 t1 Delay From channel 1 to channel 2 rising edges ( = t2-t1) Dr. L.Scucchia