Instruments that operate at radio frequency (RF) range with features like low distortion, ultra low phase noise, and portable signal generator are difficult to provide at reasonable cost.
The system shown below in Figure 1 is an entirely self-contained DC to 6GHz signal generator. It only requires the Raspberry Pi (RPi) to operate. The RF Digital-to-Analog Converter (DAC), controlled using a 100MHz Serial Peripheral Interface (SPI) from the RPi, allows for single tone, phase coherent, and fast frequency hopping across the spectrum. All the clocking is generated using an onboard crystal so no external clock source is required. All necessary power rails are converted from the RPi into various supply voltage requirements of the RF signal generator.
The system is designed to simplify the input requirements, help optimize the signal paths, and reduce external cables and components. This circuit can act as a standalone laboratory equipment, or can be incorporated as a module into automatic test equipment. Its small size makes it particularly attractive when multiple channels are required. This RPi compatible solution makes high-speed signal generation more accessible and economical.
Figure 1. EVAL-CN0511-RPIZ Evaluation Board
Figure 2. EVAL-CN0511-RPIZ Block Terminal Assignments
Figure 3. Test Setup Functional Block Diagram
Figure 4. Hardware Connections of CN0511
To set up the circuit for evaluation, consider the following steps:
The CN0511 reference design is supplied with an ultra-low phase noise CMOS voltage-controlled crystal clock oscillator. If the performance needs can’t be met, an external option is available, which is limited of up to 500MHz clock source input. And this external clock source can be connected through the on-board SMA port.
The CN0511 has a solder jumper (JP1) which configures different settings as shown below for the clock source. The default position of JP1 is set at A-COM.
Figure 5. EVAL-CN0511-RPIZ Clock Source Schematic Diagram
Figure 6. EVAL-CN-0511-RPIZ Clock Source Assignment
RPi connects to the EVAL-CN0511-RPIZ through 40-pin connector P2.
Figure 7. Input Power Supply Connection Options of CN0511
Figure 8. Input and Output Connection Guide of CN0511 Raspberry Pi with a Spectrum Analyzer and External Clock Source
The AD9166 is a high-power device that can dissipate nearly 4W depending on the user application and configuration. Cooling requirements for EVAL-CN0511-RPIZ are high and the fan should always be on to regulate the temperature below 60 degrees Celsius.
Figure 9. Cooling Management Guide of CN0511
Figure 10. Overall System Setup Overview of CN0511
For the device to run, the SD card should have a preinstalled OS which is the Analog Devices Kuiper Linux, a distribution based on Raspbian for the Raspberry Pi.
It incorporates Linux device drivers for ADI products, and is created with ease of use in mind.
The reasoning behind creating this distribution is to minimize the barriers to integrating ADI hardware devices into a Linux-based system.
If a remote access in the device is required in an application, the CN0511 reference board connected to the can be remotely access by a remote PC either via LAN cable or via Wi-Fi.
Once the device has been setup, the generated Rfoutput from the CN0511 reference design can be viewed at its output terminal
In order to boot the RPi, obtain an SD card “image”, and write (or “burn”) it to a card. Refer to this guide for burning to a card: Burning SD Cards
For the Linux kernel to identify the device connected to the expansion header, update the device tree overlay. A Device Tree Overlay contains information about additional connected hardware, the EVAL-CN0511-RPIZ for this case. The overlay file is already included in the SD card and just needs to be matched to the EVAL-CN0511-RPIZ. With the RPi connected to the EVAL-CN0511-RPIZ and booted up, open a command prompt and type the commands shown in the next figures. The command prompt can be easily accessed using one of the icons in the window header. By default, it should be the fourth icon from the left of the window header.
analog@analog:~$ sudo nano /boot/config.txt
This will bring up the file in terminal. Scroll down until the line that begins with “dtoverlay” is found, then, whatever it currently is, change it to:
dtoverlay=rpi-cn0511
Save the file by Ctrl + X command. Reboot the system by typing on the command prompt:
analog@analog:~$ sudo reboot
The RPI_demo_cn0511 provides a solution for controlling RF output power and tuning from DC up to 6GHz, using an EVAL-CN0511-RPIZ hat installed on an RPi base board. The user interface is implemented through wired and wireless connection.
The EVAL-CN0511-RPIZ can be evaluated with the IIO Oscilloscope. Customers can use the CN0511 plugin tab, debug tab, and the DMM tab. Various controls and diagnostics are available in these plugins.
The CN0511 plugin tab provides a simple user interface to control the EVAL-CN0511-RPIZ as a signal generator.
Figure 11. Graphical User Interface (GUI) window of ADI IIO Oscilloscope with CN0511 Plugin
The debug tab provides direct access to IIO device and channel attributes as well as the registers of the CN0511 components. The IIO attributes and registers can be read and written for advanced configuration and information.
The DMM tab provides temperature readings for ADF4372 and AD9166 using internal temperature sensors on both devices.
EVAL-CN0511-RPIZ Design & Integration Files
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