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Question about the IQ calibration range (how many dB?) and (how many degrees) ADC16DX370 and DAC38J84 can achieve?

Matt Yu
Prodigy 40 points
Other Parts Discussed in Thread: DAC38J84, ADC16DX370

Hi, 

We plan to use FMC144 (DAC/ADC module) from 4DSP.corp,  which use  ADC16DX370 and DAC38J84  for ADC and DAC respectively. 

We raise questions to 4DSP about the IQ calibration range (how many dB?) and (how many degrees) ADC16DX370 and DAC38J84 can achieve? 

But they don't have information in detail. 

Could Ti advise including 

1)  IQ calibration range (how many dB?) and (how many degrees) ADC16DX370 can achieve using QMC(quadrature Modulation Correction)? 

2)  IQ calibration range (how many dB?) and (how many degrees) DAC38J84  can achieve ?  Is  the gain imbalance: is +/-2%?  and the phase imbalance be 

      within +/-0.5 deg?  (Is there any limitation If the imbalances from our analog differential components,etc is large)

  • 0
    TI__Guru* 78154 points
    Hi,

    The topic of IQ calibration involves the entire transmitter and receiver system, and you will need to consider factors such as frequency placement and the type of modulator/demodulator being used.

    For the DAC38J84, you may refer to page 71 and 72 of the datasheet for details of gain/phase imbalance adjustment. This adjustment assumes that the gain/phase imbalance from the DAC output to the analog quadrature modulator is frequency independent (i.e. fixed gain/phase imbalance). If there are additional filtering or PCB trace imbalance causing group delay difference, the gain/phase imbalance will be time dependent and frequency dependent (i.e. delta phase = group delay*delta frequency). This type of gain/phase imbalance varies with IF frequency, and can be adjusted with our fractional delay filter. You may need to perform some testing on your side and create your own algorithms to exercise these options for sideband suppression. With the FMC144, chances are you will be hooking up DAC to modulator through SMP cables, so you will need to consider the group delay from the matching of the cables.

    My colleague can comment more on the ADC16DX370. I believe you may need to perform your own sideband adjustment on the baseband processing for the demodulator+ADC signal chain as well.

    -Kang
  • 0 in reply to Kang Hsia
    TI__Expert 4340 points

    As described in the datasheet, the channel-to-channel full scale range mismatch of the ADC16DX370 is 0.07dB typical. Amplitude mismatch will also vary across frequency like the phase mismatch, but both of these will probably depend more on the filtering (bandwidth limitation) in front of the ADC and the associated component variability than on the ADC itself.

    Regards, Josh

  • 0 in reply to Kang Hsia
    Prodigy 40 points

    Hi, Kang. 

    Thanks for the information. 

    I have check the datasheet, so for amplitude and phase imbalance correction by QMC of DAC38J84, the range is 

    Gain calibration range:  0~1.9990  dB

    Phase calibration range: -0.5~ 0.49975 degree

    Is the unit dB correct?  

    Matt.

  • 0 in reply to Joshua Carnes
    Prodigy 40 points
    Hi, Josh.
    Thanks for the information. As I check the datasheet of ADC16DX370, in table 16 (Imbalance Adjust, Channel A), Analog input amplitude correction can be achieved by changing the resistance, and the register( decimal) is from 0 to 7, what's the range corresponding to gain in terms of dB?
    and also analog input phase correction can be achieved by changing the capacitance, the register( decimal) is from 0 to 15, what's the range corresponding to phase in terms of degree?
    Please advise, thanks.

    Matt.
  • 0 in reply to Matt Yu
    TI__Expert 4340 points

    Hi Matt,

    The input balance correction on the ADC16DX370 is used to correct the balance of the input different signal, to make sure the the - input has the same amplitude and 180 phase compared to the + input. This feature is not used to correct for amplitude or phase differences between channels for I/Q correction.

    Regards, Josh

  • 0 in reply to Matt Yu
    TI__Guru* 78154 points

    Gain adjustment is in linear scale (i.e. 0x to 1.9999x). 

  • 0 in reply to Joshua Carnes
    Prodigy 40 points

    Hi, Josh. 

    Thanks for remind. So does ADC16DX370 itself have any channel to channel phase and gain imbalance correction (just like DAC38J84)? It seems not, right? 

    and by the way, also for ADC16DX370, we saw a high-pass filter can be enabled to do the DC-offset correction. Can we know the cufoff frequency of the HPF and the attenuation information in the stop band (vs freq) ?

    Thanks.

    Matt.

     

  • 0 in reply to Matt Yu
    TI__Expert 4340 points

    Matt,

    The ADC16DX370 does not have channel-to-channel correction.

    The 3dB BW of the DC offset correction filter are documented on page 41 of the datasheet. We will not be able to provide a full frequency response.

    Regards, Josh