Analog Devices is an Mbed Partner and develops code on the platform for multiple products. The AD9106 and AD9102 Mbed-enabled evaluation boards and example Mbed codes can be used as starting point for characterizing the high-speed waveform generator digital-to-analog converters before integrating them into specific applications.
This guide will focus on how AD9106-ARDZ-EBZ/AD9102-ARDZ-EBZ works with SDP-K1 controller board developed by Analog Devices. Users are not limited to using SDP-K1 for evaluation or prototyping. The evaluation boards and the example source codes with minor changes can work with other ARM-based Mbed-enabled boards. The user interface is text based.
The evaluation setup can be powered by USB only and does not require a high-frequency waveform generator for clock input. The evaluation board has an on-board 156.25 MHz crystal oscillator. To fit the evaluation system in a small form factor and manage power consumption within USB specifications, AD9106 and AD9102 supply voltages AVDD, DVDD and CLKVDD are limited to 3.3V only.
Figure 11a. AD9106 example 3 waveforms out of RF transformers | Figure 11b. AD9106 example 5 waveforms out of RF transformers
Figure 12a. AD9102 example 3 waveform out of RF transformer | Figure 12b. AD9102 example 5 waveform out of RF transformer
Figure 13a. Restarting the program | Figure 13b. Exiting the program
Figure 14a. DAC clock is connected to on-board oscillator (default) | Figure 14b. DAC clock is connected to J10
By default, DAC CLKP and CLKN are connected to the differential outputs of the on-board crystal oscillator as shown in Figure 14a. If clock frequency other than 156.25 MHz is desired, an off-board clock source can be used and connected to J10. Change JP1 and JP2 connections first as shown in Figure 14b.
Figure 15a. DAC ouputs are connected to RF transformers (default) | Figure 15b. DAC ouputs are connected to ADA4817-2 amplifiers
Figure 16a. SMA output connectors are connected to RF transformers (default)
Figure 16b. SMA output connectors are connected to ADA4817-2 amplifier outputs
The waveforms in Figures 11a to 12c can also be observed out of the on-board amplifiers. To do this, disconnect the DAC outputs from the RF transformers and connect them to the corresponding amplifiers as shown in Figure 15b, then disconnect the SMA connectors from the RF transformers and connect them to the amplifier outputs as shown in Figure 16b. It is expected that the amplifier output amplitudes will be higher. Lower signal amplitudes out of the RF transformers are due to insertion loss and output voltage division resulting from impedance matching between the secondary and primary sides.
Figure 17a. AD9106 example 1 waveforms out of ADA4817-2 | Figure 17b. AD9106 example 2 waveforms out of ADA4817-2
Figure 17c. AD9106 example 4 waveforms out of ADA4817-2 | Figure 17d. AD9106 example 6 waveforms out of ADA4817-2
Figure 18a. AD9102 example 1 waveform out of ADA4817 | Figure 18b. AD9102 example 2 waveform out of ADA4817
Figure 18c. AD9102 example 4 waveform out of ADA4817
To properly observe the other patterns out of the amplifiers, replace C25, C26, C54, and C55 with 0Ω resistors or remove the capacitors then solder each pair of pads together. Waveforms are shown in Figures 17a to 18c.
The common-mode voltage of the amplifier outputs can also be changed by installing resistors for DC offset correction of amplifier inputs. Refer to Table 1. Keep C25, C26, C54, and C55 pads shorted.
The on-board amplifiers can be characterized using off-board power supplies by removing E1 and E2 then connecting 5.2V 0.2A across TP5 and ground and -5.2V 0.2A across TP4 and ground.
When tapping to the evaluation board outputs, users are not limited to the SMA jacks. P14 headers are provided as alternative connectors but performance is not as good as when using SMA connectors.
The EVAL-AD910x Example Mbed Codes can be used as starting point for developing firmware for targeted applications. The codes in the repositories below demonstrates how to setup SPI communication between the ARM-based Mbed-enabled hardware, SDP-K1, and the waveform generator DACs, AD9106 or AD9102.
To import the program files to the Mbed compiler as discussed in the Quick Start Guide, the user should have a free Mbed account and is logged on to https://os.mbed.com/. After successful program import, the user is free to use and modify the codes without violating the Analog Devices Inc. Software License Agreement in the License.txt file.
Each file and each of the functions in the files have short descriptions or briefs. This section will focus on how several files and functions can be modified using the Mbed online compiler.
Figure 19. SPI protocol definitions, example SRAM vectors, and example SPI register configurations in config.h
Aside from choosing the active device as shown in the Quick Start Guide, SPI protocol parameters particularly the clock frequency can be set at the application-level codes. Word length WORD_LEN and polarity POL need not be changed and are already set specifically for AD9106 and AD9102. Refer to Mbed OS 6 SPI Documentation for more information on these parameters.
Instructions on setting the SPI clock (SCLK) frequency are already provided in config.h as shown in Figure 19. The reason why SCLK can only be set to a number of fixed frequencies is discussed in this Mbed wiki page on SPI output clock frequency. SPI lines out of the Arduino headers or SPI1 module of the SDP-K1 ARM processor, uses 90MHz peripheral clock. Refer to these relevant source codes:
Figure 20. Device-specific I/O pins and functions declarations in ad910x.h
Initialization of digital I/O pins connected to the DAC being evaluated, and declaration of SPI register addresses and device-specific functions are in ad910x.h. See Figure 20. The functions are implemented in ad910x.cpp. The Mbed platform drivers allow setup of 4-wire SPI interface. Refer to Mbed documentation for other configurations.
SRAM Vectors in config.h can be easily modified for a specific application. For both AD9106 and AD9102, there are 4096 addresses in the on-chip SRAM. Word length is 14 bits for AD9102, 12 bits for AD9106, and is left justified. For AD9102, data should be written in bits [15:2] and for AD9106 in bits [15:4] of each SRAM address.
Figure 21a. Waveforms that can be generated using DPG Lite
Figure 21b. Waveform vector generation using DPG Lite
Although the SRAM vectors can be modified manually, it will be more convenient to create new vectors using DPG Lite. Shown in Figure 21a are types of waveforms that can be generated using the software.
When creating data vectors for AD9106 and AD9102, make sure to choose the proper DAC resolution and leave the Unsigned Data box unchecked. A continuous wave vector with record length of 4096 can be created but the SRAM can also be composed of different types of waveforms like in the example in Figure 21b where there are 3 vectors with combined record length of 4096. These can be saved as text files and integrated into the source code.
It is not required to write to all 4096 addresses. Each DAC channel in a device can fetch data from a fixed SRAM address to another. The start and stop addresses can be set using the following registers:
SRAM data format or code follows two’s complement notation. Refer to Table 3 for the equivalent current output for an input code. 14-bit code should be shifted left by 2 bits before writing it to AD9102 SRAM while 12-bit code should be shifted left by 4 bits before writing it to AD9106 SRAM. Alternatively, 14-bit data shifted left by 2 bits can be written to AD9106 SRAM but the last two bits with be truncated. This is why in AD910x_update_sram() function in ad910x.cpp, SRAM data is by default shifted 2 bits to the left. Refer to Figure 22.
Figure 22. Function that writes to on-chip SRAM in ad910x.cpp
AD910x_print_sram() function is declared in ad910x.h and implemented in ad910x.cpp but is by default not called in the main program main.cpp. The function can be used to print in the console n number of data words from SRAM. This can be done by calling the function in main.cpp after an AD910x_update_sram().
AD9106 and AD9102 have similar register maps. The latter only has less number of registers that affect device functionality because writing to registers for the 3 other DAC channels will only have an effect to AD9106. Nonetheless, the defined SPI registers address in ad910x.h will work for both devices.
The SPI register addresses were written as comment in config.h and aligned with example SPI register values for user’s convenience. Same as the SRAM vectors, these SPI register values can also be easily modified for specific applications. Refer to the device datasheets for the SPI register descriptions.
Figure 23. Power supply enable/shutdown pins in main.cpp
Other I/Os like the ones connected to the EN pin of the on-board oscillator supply, CVDDX, and to the SHDN_N pin of the on-board amplifier supply, LT3472, are defined in main.cpp.
As shown in Figure 23, if external or off-board clock source is chosen, en_cvddx = 0 and no power is supplied to CVDDX. If the on-board oscillator is chosen, en_cvddx = 1 and 3.3V is supplied to CVDDX.
If the user confirms that the DAC outputs are connected to the on-board amplifiers, shdn_n_lt3472 = 1 and 5.2V and -5.2V are supplied to the amplifiers provided a wall wart is connected to SDP-K1 or the evaluation board. Otherwise, shdn_n_lt3472 = 0 and the amplifiers are not powered up.
This section lists items to check and practices to use when debugging any unexpected performance of a board. If unexpected results occur