The AD7091R is a 12-bit, ultra low power, successive approximation ADC. The AD7091R operates from a single 2.7 V to 5.25 V power supply and is capable of achieving a sampling rate of 1 MSPS. The part contains a wide bandwidth track-and-hold amplifier that can handle input frequencies in excess of 7 MHz. The AD7091R also features an on-chip conversion clock, accurate reference and high-speed serial interface.
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).
If you are not familiar with LX9 and/or Xilix tools, please visit
http://www.xilinx.com/products/boards-and-kits/AES-S6MB-LX9.htm for details.
If you are not familiar with Nexys™3 and/or Xilix tools, please visit
http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,400,897&Prod=NEXYS3 for details.
Extract the project from the archive file (AD7091R_<board_name>.zip) to the location you desire.
To begin, connect the PmodAD6 to J5 connector of LX9 board, pins 1 to 6 (see image below). You can use an extension cable for ease of use. Connect the USB cables from the PC to the board. 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 PmodAD6 to JA connector of Nexys™3 board, pins JA1 to JA6 (see image below). You can use an extension cable for ease of use. 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 and then program the device using the bit file provided in the project *.zip archive, located in the “sw” folder (../ad7091R/sw/AD7091R.bit).
If programming was successful, you should be seeing messages appear on the terminal window as shown in the figures below. After programming the AD7091R, you will be asked you to set the value of VREF.
If you use the default VREF(=2.5V) then just press [Enter] and the program will display the value of the input voltage. Pressing any key will perform another conversion and display the result.
Here you are some of the errors that can appear while trying to introduce a wrong value for VREF. If any value besides 1 to 9 is entered, an error message will be displayed. If a value higher than 5250 or lower than 2700 is entered, an error message will be displayed. If entering less than 4 characters, please press [Enter] in order to validate your input. If 4 characters are entered, the result is automatically validated.
The reference design is a custom SPI Interface, containing CS, SCLK, MISO, and a CONVST signal.
The hardware SPI access allows receiving data from the AD7091R.
When using external VREF, connect the VREF signal to J2 Pin 3. The range for external VREF is 2.7V ≤ VREF ≤ AVDD.