AD5933 Pmod Xilinx FPGA Reference Design

The AD5933 is a high precision impedance converter system solution that combines an on-board frequency generator with a 12-bit, 1 MSPS, analog-to-digital converter (ADC). The frequency generator allows an external complex impedance to be excited with a known frequency. The response signal from the impedance is sampled by the on-board ADC and a discrete Fourier transform (DFT) is processed by an on-board DSP engine. The DFT algorithm returns a real (R) and imaginary (I) data-word at each output frequency. Once calibrated, the magnitude of the impedance and relative phase of the impedance at each frequency point along the sweep is easily calculated. This is done off chip using the real and imaginary register contents, which can be read from the serial I2C interface.

HW Platform(s):

• Spartan-6 LX9 Microboard (Avnet)
• Nexys™3 Spartan-6 FPGA Board (Digilent)
• Pmod-IA (Digilent)
  

System: Microblaze, AXI, UART

The bit file provided in the project *.zip file combines the FPGA bit file and the SDK elf files. It may be used for a quick check on the system. All you need is the hardware and a PC running a UART terminal and the programmer (IMPACT).

• Spartan-6 LX9 Microboard (Avnet)
• Nexys™3 Spartan-6 FPGA Board (Digilent)
• Pmod-IA (Digilent)

• Xilinx ISE 13.2 (Programmer (IMPACT) is sufficient for the demo and is available on Webpack).
• A UART terminal (Tera Term/Hyperterminal), Baud rate 115200 for the Avnet LX-9 Microboard or 9600 for the Digilent Nexys™3 Board.

Extract the project from the archive file (AD5933_<board_name>.zip) to the location you desire.

To begin, connect the Pmod-IA to J5 connector of LX9 board, pins 3 to 6 (see image below). You must use an extension cable. . Connect the USB cable from the PC to the USB-UART female connector of the board for the UART terminal. The board will be programmed through its USB male connector.

To begin, connect the Pmod-IA to JA connector of Nexys™3 board, pins JA3 to JA6 (see image below). You must use an extension cable. Connect the USB cables from the PC to the board, one for programming (Digilent USB device) and one for the UART terminal (FT232R USB UART).

Start IMPACT, and double click “Boundary Scan”. Right click and select Initialize Chain. The program should recognize the Spartan 6 device (see screenshot below). Start a UART terminal (set to appropiate baud rate) and then program the device using the bit file provided in the project *.zip archive, located in the “sw” folder (../ad5933/sw/AD5933.bit).

If programming was successful, you should be seeing messages appear on the terminal window as shown in the figures below. After programming the AD5933 device, the program will automatically read the temperature value of the AD5933. Afterwards it will start a calibration process. Use a 47 Kohm resistor for this purpose. After calibration is complete, the user will be promped to change the 47 Kohm resistor with the desired component for measurement, and press [Enter] afterwards. The result of the measurement will be printed on the terminal window both in ohms and Kohms.

The reference design is a consists of an IIC interface between the FPGA and the Pmod-IA. Functions for setting the frequency sweeps and other parameters can be found in AD5933.c, in the “sw” folder (../ad5933/sw/AD5933.c). If you desire to use another resistor for calibration purposes, you must change the “47000” parameter for the AD5933_CalculateGainFactor function in main.c with the value of your resistor.

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