wiki:ADC_Interface

The AD9928 provides 160MHz DDR data. A very similar implementation was done for the "Time Reversal Mirror" project using a Spartan-3E chip (XC3S500E-4PQG2308) (firmware Wiki page

Here (des8.zip implementation of an 8-bit deserializer, along with two scripts (init.tcl, f5a.tcl) which simulate it.

Here (deser.zip sample. (see README.txt file in the zip archive).

Refer to UG381 and Spartan-6 Libraries and AD9928 Data Sheet

Essentially, at the top level we instantiate IBUFDS for the data, IBUFGDS for the DDR clock:

        -- (inside a generate loop)
        --
        lvds_serial: IBUFDS generic map(
		CAPACITANCE => "LOW",
                DIFF_TERM => FALSE,
                IBUF_DELAY_VALUE => "0",
		IFD_DELAY_VALUE => "0",
		IOSTANDARD => "LVDS_25") port map (
		O => serial,
		I => SERIAL_P,
	        IB => SERIAL_N);

	lvds_clk: IBUFGDS generic map(
                IOSTANDARD => "LVDS_25") port map (
                O => clk,
                I => CLK_P,
                IB => CLK_N);

Then we instantiate an IDDR2 for each serial data input. Note that phased' is the phase-adjusted clock from the DDR, and reversed' is the clock shifted 180 degrees (CLK180 output of DCM).

        doubler : IDDR2 port map(
                D  => DATA,
                Q0 => nexte,
                Q1 => nexto,
                C0 => phased,
        	C1 => reversed,
                CE => ''1',
		R  => ''0',
                S  => ''0');

In the time mirror project a DCM was used to clean the clock. This may not be necessary. In any case, the deserializer itself is just simple VHDL. Here CLOCK is the frame clock from the ADC. We probably need to generate this ourself.

        tick: process(phased)
        begin
                if phased''event and phased = '1' then
                        even <= nexte;
                        odd <= nexto;
                        odd_group <= odd_group(5 downto 0) & odd;
                        even_group <= even_group(5 downto 0) & even;
                end if;
        end process;

        tock: process(CLOCK)
        begin
                if CLOCK''event and CLOCK = '0' then
                        --current implementation assumes that msb is sent first across serial port                       
                        SAMPLE <= even_group(6)& odd_group(6)& even_group(5)& odd_group(5)&
                                even_group(4)& odd_group(4)& even_group(3)& odd_group(3)&
                                even_group(2)& odd_group(2)& even_group(1)& odd_group(1);
                end if;
        end process;

Last modified 9 years ago Last modified on Nov 8, 2013, 10:17:53 AM