Scope Tab

The Scope is a powerful time domain and frequency domain measurement tool as introduced in Unique Set of Analysis Tools and is available on all SHFLI instruments.

Features

• Two input channels
• 14 bit nominal resolution
• Fast Fourier Transform (FFT): up to 2 GHz span (800 MHz in baseband), spectral density and power conversion, choice of window functions

Description

The Scope tab serves as the graphical display for time domain data. Whenever the tab is closed or an additional one of the same type is needed, clicking the following icon will open a new instance of the tab.

Table 1: App icon and short description

Control/Tool	Option/Range	Description
Scope		Displays shots of data samples in time and frequency domain (FFT) representation.

Figure 1: LabOne UI: Scope tab - Time domain

The Scope tab consists of a plot section on the left and a configuration section on the right. The configuration section is further divided into a number of sub-tabs. It gives access to a single-channel oscilloscope that can be used to monitor a choice of signals in the time or frequency domain. Hence the X axis of the plot area is time (for time domain display, Figure 1) or frequency (for frequency domain display, Figure 3). It is possible to display the time trace and the associated FFT simultaneously by opening a second instance of the Scope tab.

The Scope records data from a single channel at up to 2 GSa/s. The channel can be selected among the two Signal Inputs. The Scope records data sets of up to 64'000 samples.

The product of the inverse sampling rate and the number of acquired points (Length) determines the total recording time for each shot. Hence, longer time intervals can be captured by reducing the sampling rate. The Scope can perform sampling rate reduction either using decimation or BW Limitation as illustrated in Figure 2. BW Limitation is activated by default, but it can be deactivated in the Advanced sub-tab. The figure shows an example of an input signal at the top, followed by the Scope output when the highest sample rate of 2 GSa/s is used. The next signal shows the Scope output when a rate reduction by a factor of 4 (i.e. 500 MSa/s) is configured and the rate reduction method of decimation is used. For decimation, a rate reduction by a factor of N is performed by only keeping every N^th sample and discarding the rest. The advantage of this method is its simplicity, but the disadvantage is that the signal is undersampled because the input filter bandwidth of the SHFLI instrument is fixed at 1 GHz. As a consequence, the Nyquist sampling criterion is no longer satisfied and aliasing effects may be observed. The default rate reduction mechanism of BW Limitation is illustrated by the lowermost signal in the figure. BW Limitation means that for a rate reduction by a factor of N, each sample produced by the Scope is computed as the average of N samples acquired at the maximum sampling rate. The effective signal bandwidth is thereby reduced and aliasing effects are largely suppressed. As can be seen from the figure, with a rate reduction by a factor of 4, every output sample is simply computed as the average of 4 consecutive samples acquired at 2 GSa/s.

Figure 2: Illustration of how the Scope output is generated in BW Limitation and decimation mode when the sampling rate is reduced from the default of 2 GSa/s to 500 MSa/s

Important

When operating in RF mode, the SHFLI’s Scope shows two traces per channel in the time domain, labeled I and Q. This is because it visualizes the data coming from the frequency mixing stage, which is composed of an in-phase and a quadrature component, similar to the data from the demodulators. In the frequency domain, this corresponds to a spectrum with symmetrical positive and negative frequencies centered around the channel’s center frequency.

The frequency domain representation is activated in the Control sub-tab by selecting Freq Domain FFT as the Horizontal Mode. It allows the user to observe the spectrum of the acquired shots of samples. All controls and settings are shared between the time domain and frequency domain representations.

The Scope supports averaging over multiple shots. The functionality is implemented by means of an exponential moving average filter with configurable filter depth. Averaging helps to suppress noise components that are uncorrelated with the main signal. It is particularly useful in combination with the Frequency Domain FFT mode where it can help to reveal harmonic signals and disturbances that might otherwise be hidden below the noise floor.

Figure 3: LabOne UI: Scope tab - Frequency domain

The Trigger sub-tab offers all the controls necessary for triggering on different signal sources. When the trigger is enabled, then oscilloscope shots are acquired whenever the trigger conditions are met. Trigger and Hysteresis levels can be indicated graphically in the plot. A disabled trigger is equivalent to continuous oscilloscope shot acquisition.

Functional Elements

Table 2: Scope tab: Control sub-tab

Control/Tool	Option/Range	Description
Single		Acquires a single shot of samples.
Channel 1/2		Selects the signal source for the corresponding scope channel. Navigate through the tree view that appears and click on the required signal. Note: Channel 2 requires the DIG option.
Enable	ON / OFF	Activates the display of the corresponding scope channel. Note: Channel 2 requires the DIG option.
Run/Stop		Runs the scope/FFT continuously.
Mode	Freq Domain (FFT)	Switches between time and frequency domain display.
	Time Domain
Sampling Rate	916 Sa/s to 60 MSa/s	Defines the sampling rate of the scope. The numeric values are rounded for display purposes. The exact values are equal to the base sampling rate divided by 2^n, where n is an integer.
Sampling Rate		Defines the sampling rate of the scope. The numeric values are rounded for display purposes. The exact values are equal to the base sampling rate divided by 2^n, where n is an integer. Warning: Due to the lack of sample averaging feature, reduced sampling rates can cause aliasing and thus artifacts in the signal spectrum. Currently, the Scope tool only supports sample decimation, but in the future it will also offer sample averaging.
Average Filter		Enable Exponential Moving Average (EMA) filter that is applied when the average of several scope shots is computed and displayed. Depending on the mode, the source data for averaging is either the Time or the Freq FFT trace.
	Off	Averaging is turned off.
	On	Consecutive scope shots are averaged with an exponential weight.
Averages	integer value	The number of shots required to reach 63% settling. Twice the number of shots yields 86% settling.
Reset		Resets the averaging filter.

For the Vertical Axis Groups, please see the table "Vertical Axis Groups description" in the section called "Vertical Axis Groups".

Table 3: Scope tab: Trigger sub-tab

Control/Tool	Option/Range	Description
Enable	ON / OFF	When triggering is enabled scope data are acquired every time the defined trigger condition is met. If disabled, scope shots are acquired continuously.
Segments	1 to 32768	Specifies the number of segments to be recorded in device memory. The maximum scope shot size is given by the available memory divided by the number of segments. This functionality requires the DIG option.
Shown Trigger	integer value	Displays the number of triggered events since last start.

Table 4: Scope tab: Advanced sub-tab

Control/Tool	Option/Range	Description
FFT Window	Cosine squared (ring-down)	Several different FFT windows to choose from. Each window function results in a different trade-off between amplitude accuracy and spectral leakage. Please check the literature to find the window function that best suits your needs.
	Rectangular
	Hann
	Hamming
	Blackman Harris
	Flat Top
	Exponential (ring-down)
	Cosine (ring-down)
Resolution (Hz)	mHz to Hz	Spectral resolution defined by the reciprocal acquisition time (sample rate, number of samples recorded).
Power Correction	ON / OFF	When activated, applies power correction to the spectrum to compensate for the shift that the window function causes. Power correction is useful for noise measurements to correct the noise floor. When deactivated, amplitude compensation is applied which corrects the peak amplitudes of coherent tones.
Absolute Frequency	ON / OFF	Shifts x-axis labeling to show the absolute frequency in the center as opposed to 0 Hz, when turned off.
Spectral Density	ON / OFF	Calculate and show the spectral density. If power is enabled the power spectral density value is calculated. The spectral density is used to analyze noise.
Power	ON / OFF	Calculate and show the power value. To extract power spectral density (PSD) this button should be enabled together with Spectral Density.
Persistence	ON / OFF	Keeps previous scope shots in the display. The color scheme visualizes the number of occurrences at certain positions in time and amplitude by a multi-color scheme.
BW Limit		Selects between sample decimation and sample averaging. Averaging avoids aliasing, but may conceal signal peaks.
	OFF	Selects sample decimation for sample rates lower than the maximal available sampling rate.
	ON	Selects sample averaging for sample rates lower than the maximal available sampling rate.
Rate		Streaming rate of the scope channels. The streaming rate can be adjusted independent from the scope sampling rate. The maximum rate depends on the interface used for transfer. Note: scope streaming requires the DIG option.

Table 5: Scope tab: History sub-tab

Control/Tool	Option/Range	Description
History	History	Each entry in the list corresponds to a single trace in the history. The number of traces displayed in the plot is limited to 20. Use the toggle buttons to hide or show individual traces. Use the color picker to change the color of a trace in the plot. Double click on a list entry to edit its name.
Length	integer value	Maximum number of records in the history. The number of entries displayed in the list is limited to the 100 most recent ones.
Clear All		Remove all records from the history list.
Clear		Remove selected records from the history list.
Load file		Load data from a file into the history. Loading does not change the data type and range displayed in the plot, this has to be adapted manually if data is not shown.
Name		Enter a name which is used as a folder name to save the history into. An additional three digit counter is added to the folder name to identify consecutive saves into the same folder name.
Auto Save		Activate autosaving. When activated, any measurements already in the history are saved. Each subsequent measurement is then also saved. The autosave directory is identified by the text "autosave" in the name, e.g. "sweep_autosave_001". If autosave is active during continuous running of the module, each successive measurement is saved to the same directory. For single shot operation, a new directory is created containing all measurements in the history. Depending on the file format, the measurements are either appended to the same file, or saved in individual files. For HDF5 and ZView formats, measurements are appended to the same file. For MATLAB and SXM formats, each measurement is saved in a separate file.
File Format		Select the file format in which to save the data.
Save		Save the traces in the history to a file accessible in the File Manager tab. The file contains the signals in the Vertical Axis Groups of the Control sub-tab. The data that is saved depends on the selection from the pull-down list. Save All: All traces are saved. Save Sel: The selected traces are saved.

For the Math sub-tab please see the table "Plot math description" in the section called "Cursors and Math".