This chapter gives an overview of the FPGA/CPLD-based solutions found during the research process.
In particular, the differences of the products in terms of performance, features, price and the applied fundamental technology should be further discussed.
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== FPGA-Oscilloscope California Institute of Technology
The FPGA-Oscilloscope [1] was developed by students of the California Institute of Technology during a class project. It features two analog input channels and an 8-bit digital analyzer.
The results are displayed on a built-in LC-display which is shown in figure 1.
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image::https://es.technikum-wien.at/openlab/openlab_wiki/wikis/img/SOTA_osci/SOTA_osci_FPGA_osci.png[caption="Figure 1: ",title="FPGA-Oscilloscope by students of the California Institute of Technology (1)",height=300,align="center"]
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The device is a stand-alone product which does not need any access to additional hardware in order to be fully operational.
All functions of the oscilloscope are controlled by hardware buttons and knobs.
This results in a familiar look and feel like the controls of a traditional digital oscilloscope. The whole project is open-source and well documented.
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=== Hardware
The FPGA Oscilloscope uses a Altera Cyclone III FPGA which runs a NIOS II [2] softcore. The structure of the FPGA design and the relations to peripheral hardware is shown in figure 2.
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image::https://es.technikum-wien.at/openlab/openlab_wiki/wikis/img/SOTA_osci/SOTA_osci_FPGA_osci_block.png[caption="Figure 2: ",title="Block diagram of the FPGA-Oscilloscope (1)",height=400,align="center"]
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A AD9288 ADC, capable of capturing at 100MSa/s, is directly connected to the FPGA.
Besides the softcore the FPGA also contains logic for the LC-display, buttons and rotary switches as well as a trigger logic.
The FPGA is also interfacing with a flash component, as well as SRAM and VRAM for the display.
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=== Specification
As mentioned by the manual of the FPGA-Oscilloscope [3], the device is able to measure analog signals up to a maximum frequency of about 5MHz.
In terms of voltage it can handle -12V to +12V signals. The digital inputs features the same bandwidth specifications and are designed to capture 5V- and 3.3V-logic signals.
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Table 1 summarizes the specifications and the pricing of this project.
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image::https://es.technikum-wien.at/openlab/openlab_wiki/wikis/img/SOTA_osci/SOTA_osci_FPGA_osci_table1.PNG[caption="Table 1: ",title="Specifications of the FPGA-Oscilloscope",align="center"]
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The price of the whole project is derived from the Bill-of-Materials of the FPGA-Oscilloscope project. +
It is an approximate estimation because of missing information regarding the used components and pricing.
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== OsciPrime
The OsciPrime [4] was developed at the University of Applied Sciences Northwestern Switzerland in 2010 as part of multiple bachelor theses.
In contrast to the typical way of displaying the measured results, this device connects to hardware running Android-OS.
Figure 3 shows the PCB of the OsciPrime with some of its components named.
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image::https://es.technikum-wien.at/openlab/openlab_wiki/wikis/img/SOTA_osci/SOTA_osci_Osciprime_board.png[caption="Figure 3: ",title="Picture of the OsciPrime hardware (4)",height=350,align="center"]
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The Android application as well as the design of the CPLD are open-source. Schematics and layouts are available for free.
The whole project is very well documented and a pre-built device can be purchased for approx. 261 euro.
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=== Hardware
The heart of the OsciPrime are the 6 MSa/s capable ADC08100 ADCs.
Those 8 bit ADCs are directly connected to a Xilinx Coolrunner II CPLD, which arranges the sampled data for a USB-controller.
The USB-controller, a Cypress FX2, then outputs the data to a android running device.
The CPLD acts as master towards the FX2 and pushes the sampled signal into its FIFO memory. This stabilizes data transmission.
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=== Android application
The GUI of the Android application, shown in figure 4, has a similar structure to that of a typical digital oscilloscope.
To display the measured waveform, the application uses the whole screen of the device. Settings are hidden under additional menus, accessible through on-screen buttons.
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image::https://es.technikum-wien.at/openlab/openlab_wiki/wikis/img/SOTA_osci/SOTA_osci_Osciprime_gui.png[caption="Figure 4: ",title="Screenshot of the OsciPrime Android application (5)",height=320,align="center"]
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As additional feature this software is capable of visualizing audio signals as well. Those can be inputed by a built-in microphone or by attaching a external source via a jack plug.
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=== Specification
Table 2 summarizes the specifications and the pricing of the OsciPrime oscilloscope.
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image::https://es.technikum-wien.at/openlab/openlab_wiki/wikis/img/SOTA_osci/SOTA_osci_Osciprime_table2.PNG[caption="Table 2: ",title="Specifications of the OsciPrime oscilloscope",align="center"]
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Featuring two analog channels, each connected to a ADC08100 ADC, the OsciPrime is able to measure signals up to a frequency of 8 MHz.
The ADCs are sampling at 6 MSa/s with a 8 bit resolution. The voltage of the signal can range between -16 to +16V.
This project is commercial available and can be purchased at the companies website [4].
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== PicoScope 2200 Series
Pico Technology, a company providing portable measurement equipment, lists a wide range of USB connected oscilloscopes ranging from 10 up to 200 MHz of input bandwidth.
Figure 5 shows the PicoScope and the included accessories.
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image::https://es.technikum-wien.at/openlab/openlab_wiki/wikis/img/SOTA_osci/SOTA_osci_pico_package.jpg[caption="Figure 5: ",title="PicoScope and accessories (6)",height=320,align="center"]
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The one with 10 MHz bandwidth retails for € 95.59 without a pair of oscilloscope probes. This commercial product is closed source and only limited information off the hardware is available.
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=== PC-software
The interface of the PicoScope software features a customizable split-screen which enables multiple channels, or different views of the signals, to be shown at the same time.
Therefore, as shown in figure 6, it is possible to look at a signal over time while observing the spectrum of the signal.
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image::https://es.technikum-wien.at/openlab/openlab_wiki/wikis/img/SOTA_osci/SOTA_osci_pico_soft.png[caption="Figure 6: ",title="User interface of the PicoScope software showing the split-screen feature (6)",height=320,align="center"]
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As an additional feature the PicoScope software provides some math calculation, like addition, subtraction or filters, applied on the displayed input signal.
Also it is possible to let the program trigger an action when different events occur. For example it can play a sound if the buffer is full.
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=== Specification
The relevant model of the PicoScope 2200 Series [6], regarding this state of the art research,
is the PicoScope 2204A. This two channel digital oscilloscope is able to measure signals up to
a frequency of 10 MHz and 40V peak to peak voltage as the maximum values. As an additional
feature the PicoScope also includes a signal generator, which enables analog waveform generation.
It is able to generate all typical waveforms (sine, square, triangle, ...) at a maximum
frequency of 100 kHz and 4V peak to peak voltage. The PicoScope is also able to capture
digital signals and decode the following protocols: CAN, LIN, I2C, UART/RS232, SPI, I2S and
FlexRay.
Table 3 lists some relevant specifications of the PicoScope oscilloscope.
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image::https://es.technikum-wien.at/openlab/openlab_wiki/wikis/img/SOTA_osci/SOTA_osci_pico_table.PNG[caption="Table 3: ",title="Specifications of the PicoScope 2204A oscilloscope",align="center"]
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The PicoScope 2204A is the only FPGA/CPLD-based oscilloscope, at a price range of ~100€, which features ETS.
Non of the open-source projects found during the research are able to perform signal acquisition using ETS.
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== Bibliography
. CALIFORNIA INSTITUTE OF TECHNOLOGY: _GitHub webpage of the FPGA-Oscillopscope project_ [Online] https://github.com/agural/FPGA-Oscilloscope[GitHub webpage of the FPGA-Oscillopscope project]
. ALTERA CORPORATION: _NIOS II softcore - overview_ [Online] https://www.altera.com/products/processors/overview.html[NIOS II softcore - overview]
. GURAL, A.: _FPGA Oscilloscope Manual_, California Institute of Technology, July 2014
. NEXUS-COMPUTING SWITZERLAND: _OsciPrime - main webpage_ [Online] http://www.osciprime.com/index.php?p=project[OsciPrime - main webpage]
. NEXUS-COMPUTING SWITZERLAND: _OsciPrime_, Techn. Rep, Nexus-Computing Switzerland, August 2010
