Introduction

Please see DSPsandbox/AD9958-real-time-RF-source.

Python API and Examples

The Python API is available by adding the AD9958 folder into the working directory of your Python interpreter. A full documentation is available here.

Please refer to the provided Examples for a detailed implementation of the different functionalities of the AD9958. Note that when downloading the current repository the set of examples are ready to use (it is not necessary to move AD9958 into the Examples folder).

Hardware

• AD9958 eval board. Dual channel DDS with a DAC sampling rate of upt to 500 MHz. For further details please check the documentation on the AD9958 and the AD9958 evaluation board.

• chipKIT Max32. PIC32 development board with a 80MHz on board clock. This microcontroller recieves the requested RF setting over its serial port and sets the corresponding registers on the AD9958 via an SPI bus. For detailed information please refer to the chipKIT Max 32 reference manual, the PIC32MX5XX/6XX/7XX data sheet and the more complete PIC32MX Familiy Reference Manual.

• Reference RF clock for operating the DDS. In order to achieve the maximum sampling rate of the AD9958 a minimum clock frequency of 25 MHz is required. Please refer to the AD9958 eval board documentation for the max/min ratings in terms of power and frequency.

• Linear volatge regulators for supplying the 3.3V and 1.8V required by the Ad9958 eval board. A good example of a LM317T variable voltage regulator diagram can be found here.

• Computer with a Python 2.7 distribution installed (my personal preference is to directly install the appropiate Anaconda distribution). Please note that the current project was developed under Python 2.7, the compatibility with Python 3 has not been tested yet. In order to programm the chipKIT Max32, the Arduino IDE and an additional board manager have to be installed. The whole procedure is well explained here.

• RF Transformer (optional). By default, the two DAC outputs of the AD9958 eval board are decoupled by using ADTT1-1 RF transformers, which operate from 0.3-300 MHz. For my application lower RF frequencies were required and I replaced the transformers by two ADT1-6T+ (dynamic range of 0.03-125 MHz).

Setting up the AD9958 eval board

Please follow the instructions in the above mentioned documentation for:

• Setting the jumpers for External Control.
• Setting the jumper for External REF_CLK.
• Proving the 1.8V and 3.3V bias voltages on the required connectors.

Connections between AD9958 eval board chipKit Max32

In the following table the wiring between the microcontroller and the Manual I/0 Control Header of the AD9958 eval board are described. Please note that although the Manual I/O Control Headers have two row of pins available only the lower one is connected to the AD9958.

AD9958 eval header	Chipkit Max32 Pin	Description
P0	30	Profile pin 0
P1	31	Profile pin 1
P2	32	Profile pin 2
P3	33	Profile pin 3
IO_UPDATE	34	IO Update
CSB	35	Chip select (SPI)
SCLK	52	Serial clock (SPI)
RESET	36	Reset
PWR_DWN	37	Power down
SDIO_3*	38	Sync I/O
SDIO_2*	50	MISO (SPI)
SDIO_1*	39	Not used
SDIO_0*	39	MOSI (SPI)
NC**	18	Trigger in
NC **	19	Trigger out

* The current project uses the Single-Bit Serial 3-Wire mode of the AD9958.

**Not connected.

Triggers

Two triggers have been implemented onto the chipKit Max32:

• Trigger in. The execution of the functions stack can be held until a rising edge is detected on the corresponding PIN 18. Please make sure to adjust the voltage level of your trigger input to 3.3V.

• Trigger out. Used for monitoring purposes (e.g. triggering the adquisition of your oscilloscope) or possible external RF switches.

Setting up the chipKit Max32

The firmware required for the chipKit Max32 microcontroller can be found in the DriverChipkit/AD9958Driver folder:

• AD9958Driver.ino -> Main code running on the ChipKit Max32. Contains the functions for the construction and execution of the functions stack.
• AD9958_definitions.h -> Definitions of functions an types used in AD9958Driver.ino.
• SPI_simple library -> Basic library for fast execution of SPI commands (avoids unused overhead).
• SerialCommand library -> Serial command interpreter. Developed by S. Rado and S. Cogswell.

For setting up the chipKit Max32 make shure you have installed the IDE and the additional board manager (explained above). After, compile and upload the AD9958Driver.ino file.

Final remark

The current repository is MIT licensed, feel free to use it, improve it and give me feedback on pau.gomez@dspsandbox.org.