how to let ad9910 output a train of  pulsed sinusodial waves

Hi, everyone.

Recently, I use a Xilinx FPGA(Spartan6-lx9tqg144) to control the ad9910. I let the AD9910 work in the DRG mode, and I got the DRG mode work, realizing the freqency sweep from 200MHz to 250MHz.

furthermore, I wanna to get the following waves, but I do not know how to make it.

Let Ti(i=1,2,3,4,5...) denote the time duration

T1 :  0-1us , AD9910 output a  200MHz sinusodial wave
T2 :  1-10us, AD9910 output none
T3 :  10-11us, AD9910 output a 200MHz sinusodial wave
T4 :  11-20us, AD9910 output none
T5 :  20-21us, AD9910 output a 202MHz sinusodial wave
T6 :  21-30us, AD9910 output none
T7 :  30-31us, AD9910 output a 202MHz sinusodial wave
T8 :  31-40us, AD9910 output none
......
The process may repeat from 200, 202, ... 249, to  250 MHz

(1) I found that, the maxium speed of the Serial Port of AD9910 is 70Mbps. that means, in 1us, 70bits are transmited at the most.
If I use the ASF Register to control the Amplitude, I should send
8+32 bits(Phase One 8bits, and Phase two 32bits) via the SPI protocol
Does it  mean that it is hard for us to update the registers in 1us?

(2) If I use the parallel data mode, Can I make it?

(3)And I found that,
If I use the ADI's AD8180(a multiplex chip, which has a 5ns channel switch time), Maybe I can control the output, but I am not so sure.

Because, I currently use the prototype board, I wanna to know How to use the AD9910 to Control the output amplitude?


Any advise are appreciated.
Thank you

JiongWU

  • It appears your desire to control amplitude amounts to simply turning the output off and on. If so, I would recommend using the manual OSK mode.

    1. Prior to starting the transmission sequence, program the ASF register to full scale (you only need to do this once).
    2. Program CFR1[23]=1 (enables OSK pin for amplitude control)

    This allows you to turn the output off and on via the OSK pin (Logic 0 and Logic 1, respectively) without having to program any registers.

    Because frequency changes occur on 20us boundaries, that should allow plenty of time to write a new frequency (32 bits) via the SPI.

    The challenge will be synchronizing the SPI operation and IO_Update with the OSK pin, but it should be doable.

  • Hi Kenny,

    Thank you for your fast reply.

    I write down the operations to see if I got your ideal

    Step 1.  Let the AD9910 Work in the DRG mode. Set the ASF Register to Ful Scale.

    Step 2.  Every 20us, I write  to the Digital Ramp Limit Register(0x0B), to set the Upper Limit and The Lower Limit the same Frequency Word, e.g. 200MHz , 202MHz or  the other number.

    But the Digtal Ramp Limit Register is a 64 Bits Register. What you say is  32Bits.  I guess Maybe it is wrong.

    Maybe  Let the AD9910 work in the Single Tone Mode. But When I refer to the AD9910's datasheet,  I found that

    in the Page 21, table 5 Data Source Priority. Only the RAM mode or DRG mode correspond  to the OSK enabled conditon. And I get confused about it.

    JiongWU

  • No, I suggest using one of the single-tone profiles to control the DDS output frequency, not the DRG.

    CFR1[9]=1 enables the OSK functionality. Table 5 indicates that the amplitude source is the ASF register is when manual OSK is in effect and that the ASF register has the highest priority of any other amplitude source (except for the OSK generator, but that is only effective for auto OSK mode).

    NOTE: You will need to provide a connection from your FPGA to the OSK pin for this to work.

    SET UP:

    1. Write CFR1[9]=1 (enable OSK).
    2. Write all 1's to the ASF register (full scale amplitude).
    3. Choose a single-tone profile (Profile 0, for example). You will use Profile 0's 32-bit FTW register for changing the frequency every 20us (see OPERATION below).
    4. Set OSK pin to Logic 0 (amplitude OFF).
    5. Program Profile 0 FTW for 200MHz and issue an IO_Update (frequency is active, but output is OFF).

    OPERATION:

    Execute the loop below for all desired frequencies. The loop generates a 1us tone, 9us quiet, 1us tone, 9us quiet for each frequency.

    Loop

    1. Set OSK pin to Logic 1 (amplitude ON) and start 1us timer.
    2. Wait for 1us timer to expire, then set OSK pin to Logic 0 (amplitude OFF) and start 9us timer.
    3. Program Profile 0 FTW register for next frequency via SPI. NOTE 1 -- This does not cause a frequency change until you issue an IO_Update. NOTE 2 -- You should have no trouble writing this 32-bit register within the following 9us time window.
    4. Wait for 9us timer to expire, then set OSK pin to Logic 1 (amplitude ON) and start 1us timer.
    5. Wait for 1us timer to expire, then set OSK pin to Logic 0 (amplitude OFF), start 9us timer and issue IO_Update (previously written FTW becomes active, but no output because amplitude is OFF).
    6. Wait for 9us timer to expire.

    Repeat

  • Hi, Kenny

    Thank you for your detailed instructions guide.

    Firstly, I test the 1us ON and 1us OFF for the 202 MHz sinusoidal wave

    As you can see from the picture below. The time grid is 400 ns, and the sinusodial wave 1us tone, 1us quiet

    I can see the overshoot of the sinusodial wave when it begin to show. 

    And Could I omit the 'overshoot" of the wave as you can see from the picture below?

    Only I set the trigger level  above the normal amplitude could I get the stable display in the Tek's oscilloscope.

    If it is a normal phenomenon, I will move forward to test the other instructions that Kenny had already described above.