Pulse/Amplitude Modulation of the AD9914

Looking for information to Pulse Modulate or Amplitude Modulate using the OSK pin (66).  I have try modulating the OSK pin(66). I am not sure how to set up the rest of the register.

  • 0
    •  Analog Employees 
    on Apr 28, 2013 4:59 PM

    Hi WCB,

    OSK or Output Shift Keying pin is a digital input (active high). When the OSK features are placed in either manual or automatic mode, this pin controls the OSK function. In manual mode, it toggles the multiplier between 0 (low) and the programmed amplitude scale factor (high). In automatic mode, a low sweeps the amplitude down to zero and a high sweeps the amplitude up to the amplitude scale factor.

    I'd like to refer you at page 22 of the datasheet for more info in setting up the appropriate registers.

    Regards

    Louijie

  • Hi Louijie

    I am confused by your answer which I think is the same as the datasheet description of pin 66 (datasheet p10).

    First of all, p40 of datasheet specifies manual mode as when 'OSK enable' is 1 and 'external OSK enable' is 0. Without your description above a natural interpretation would probably be that amplitude would be set by the amplitude scale factor and the external OSK pin has no effect. I certainly did not expect what you and p10 say above. There is no other explanation of this mode anywhere else in the datasheet.

    P40 of datasheet specifies automatic mode as when 'OSK enable' is 1 and 'external OSK enable' is 1. Page 22 specifies that in this setting the output is forced to 0 when OSK pin is low and set to the amplitude scale factor value when OSK pin is high. This is the same as what you and p10 say for the manual mode, hence contradiction.

    So I am totally confused aout the OSK operation.

    If what you and p10 is the correct version then what does the amplitude sweep in automatic mode mean? what step? what rate?

    Regards

    Quang

  • 0
    •  Analog Employees 
    on Mar 12, 2014 5:42 PM

    Hi Quang,

    Before, when it was my first time to use the OSK function in the evaluation board, I also had the same confusion with you. I read the datasheet many times about the OSK function, but I only cleared myself with the confusion when I set-up the evaluation board and explored most of the configurations about the OSK function.

    There are three bits involved in setting up the modes of the OSK function (AD9914 and AD9915):

    Function Name              Function Control                 Eval Board GUI

    OSK enable                    Register Addr: 0x00 [8]          OSK enable                            

    External OSK enable       Register Addr: 0x00 [9]          External OSK enable

    OSK                               Pin 66                                  External OSK pin activate  

    The Amplitude Scaling Factor (ASF) is the value entered to control the amplitude of the output signal. This can be found on the Profile modes and DRG modes in the evaluation board. Take note: ASF values are ignored when OSK enable = 0 be it in Profile or DRG. Likewise, ASF values are latched when  OSK enable = 1.

    External OSK enable acts as a mask to the OSK/External OSK pin activate. So if it is set(1) then OSK/External OSK pin activate is enabled. Otherwise, it is ignored.

    If OSK/External OSK pin activate  = 1, The amplitude of the signal is equal to ASF. Otherwise, the amplitude is zero.

    The table summarizes the behaviour of the OSK functionality

    OSK Enable External OSK enable OSK/External OSK pin activate  Mode
    0 X X ASF Registers Ignored
    1 0 X

    ASF Registers Enabled

    Amplitude = ASF

    1 1 0 Amplitude = 0
    1 1 1 Amplitude = ASF


    Best Regards

    Louijie


  • Thanks Louijie

    Makes sense. To be honest this is what I had expected, just waiting for your confirmation. Basically what is said in page 10 about the OSK pin is complete rubbish, it is not only confusing but also wrong, without this everyone would have the same understanding as you just explained by reading the other parts about OSK.

    I have one more question. For the external OSK pin function you only mentioned ASF for Profiles and DRG modes, what about AMP in Parallel data mode? does the external OSK operation has the same effect here?

    Cheers

    Quang

  • 0
    •  Analog Employees 
    on Mar 13, 2014 6:54 PM

    Hi Quang,

    The datasheet says that the OSK enable bit should be set when you want to use AMP in direct conversion mode. I tried it in the setup and it does behave as indicated. Just an added note, you must disable the profile mode when you want to use direct conversion.

    Cheers

    Louijie