TRF370417 / IQ Error and detail of Adjusted (Optimized) Carrier Feedthrough

Ryuji:

<Q1: Phase error and Amplitude Error>
Could you please let me know the "IQ phase error vs. Frequency" and "IQ amplitude error vs. Frequency" in the attached image?

RJH>> The TRF3704 does not specify phase and amplitude imbalance independently. Instead, there is a spec for sideband rejection vs. frequency in the datasheet.  Sideband rejection is a parameter that combines the effect of amplitude and phase imbalance and does impact EVM% measurements for ZIF applications.  The SBS spec for the TRF3704 is around 40 dB which roughly corresponds to 0.5 degree phase imbalance or less and 0.1 dB of amplitude imbalance or less.

<Q2 : Measurement method and structure>
Please let me know the measurement method and structure for EVM, IQ phase error and IQ amplitude error.

RJH>> To make an EVM% measurement you will need specialized instruments that can generate an appropriate modulated signal and receive/demodulate the modulated signal.  The receiver instrument can discern amplitude and phase error from a standard input pattern.  Alternatively, you can measure sideband rejection to get a sense fo the performance that will impact an EVM% measurement.

<Q3 : Adjusted (Optimized) Carrier Feedthrough>
There is the description of "iteratively adjusted around their theoretical value of VCM" in the datasheet P.23.
Could you please let me know the detail of iteratively adjustment ?
Does TRF370417 optimize the VCM of BBIN,P, BBQI,P?

RJH>> Negative.  The Vcm is supplied externally.  Usually this is supplied directly from a DAC or through the DAC and a translation network.  TI's high performance DACs provide a digital feature that allows the user to fine tune the common mode that drives the modulator.  This adjustment is the one that can be done iteratively to optimize the carrier suppression.  Note, the TI DAC also provides a feature to adjust the amplitude and phase to optimize for sideband rejection.  You can check out DAC38H84 or DAC38J84 as an example. 

Hello RJH san,

Thank you for your reply.
I have the question to your reply.

<Q1: Phase error and Amplitude Error>
RJH>> The TRF3704 does not specify phase and amplitude imbalance independently. Instead, there is a spec for sideband rejection vs. frequency in the datasheet.  Sideband rejection is a parameter that combines the effect of amplitude and phase imbalance and does impact EVM% measurements for ZIF applications.  The SBS spec for the TRF3704 is around 40 dB which roughly corresponds to 0.5 degree phase imbalance or less and 0.1 dB of amplitude imbalance or less.

RYUJI>>Could you please let me know the calculation from SBS to phase imbalance and amplitude imbalance?
                I'm sorry but I can't undersdand the corresnponds method from -40dBc of Sideband suppression to 0.5 degree phase imparance or less and 0.1dB  of amplitude imbalance or less.

<Q2 : Measurement method and structure>
RJH>> To make an EVM% measurement you will need specialized instruments that can generate an appropriate modulated signal and receive/demodulate the modulated signal.  The receiver instrument can discern amplitude and phase error from a standard input pattern.  Alternatively, you can measure sideband rejection to get a sense fo the performance that will impact an EVM% measurement.

RYUJI>> Are there the measurement system picture which you can share with us?


<Q3 : Adjusted (Optimized) Carrier Feedthrough>
RJH>> Negative.  The Vcm is supplied externally.  Usually this is supplied directly from a DAC or through the DAC and a translation network.  TI's high performance DACs provide a digital feature that allows the user to fine tune the common mode that drives the modulator.  This adjustment is the one that can be done iteratively to optimize the carrier suppression.  Note, the TI DAC also provides a feature to adjust the amplitude and phase to optimize for sideband rejection.  You can check out DAC38H84 or DAC38J84 as an example. 

RYUJI>> I understood that we adjust the DC offset of BBIP/N and BBQP/N by high performance DAC.
Could you please let me know the ajustment method or example?
If there is the app. note, please let me know.

Best Regards,
Ryuji Asaka

            

RYUJI>>Could you please let me know the calculation from SBS to phase imbalance and amplitude imbalance?
                I'm sorry but I can't undersdand the corresnponds method from -40dBc of Sideband suppression to 0.5 degree phase imparance or less and 0.1dB  of amplitude imbalance or less.

RJH>> The equation is comprised of two variables: amplitude imblance and phase imbalance.

                      SBS = sqrt(1+a^2-2acos(theta))

    where a = amplitude imbalance and theta = phase imbalance.  (Note the equation requires the parameters in linear form whereas SBS and amplitude imbalance are usually expressed in dB form so the appropriate conversions are required.

This equation can be used to generate constant cancellation curves that will give an indication of amplitude and phase imbalance.

8080.CCcurves.pdf

RYUJI>> Are there the measurement system picture which you can share with us?

RJH>> In the TRF3704 datasheet in the tables there is the EVM% results at some different frequencies.  I do not have a good picture handy to show for the TX side.

 RYUJI>> I understood that we adjust the DC offset of BBIP/N and BBQP/N by high performance DAC.
Could you please let me know the ajustment method or example?
If there is the app. note, please let me know

RJH>> You can check out the datasheet for the DAC3484.  There is a good explanation of the QMC feature and the DC offset adjustment feature.