Quadrature phase error in RX stream

Hi,
I have tested the RX path of our board over wide range of frequencies 900MHz to 2000MHz. Below I have listed measured IQ phase imbalances of select frequencies

950MHz - 12 degree phase error
1200MHz  - 12 degree phase error
1500MHz - 1.2 degree phase error
2000MHz - 2 degree phase error

The operating range for the board we purchased is 1200 to 2000 MHz. There is a concern over the large phase imbalance at the low end of the operating band.  Is this something you are aware of and do you know if there is a fix for it? What component introduces this phase error? Is it the TRF371125? Other quadrature demodulator devices specify an IQ phase error of .5 degrees over the operating frequency range. The TRF3711 does not have that spec anywhere on the datasheet.

Regards,
Stan

Oh I also wanted to add another frequency because I just realized it's the high end of the board spec

3000MHz - .5 degree phase error

Hi Stan,


[size=0pt]The typical image rejection performance for the TRF3711 is specified at 40 dBc.  The breakdown between phase imbalance and amplitude balance is not specified.  There are a few factors that will impact the phase balance/image rejection.[/size]
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I guess the biggest factor is the balun used to make the differential input to the TRF3711. The datasheet ([/size]http://www.macomtech.com/datasheets/ETC1-1-13.pdf) graph seems to match quite a bit with your measurements.
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[/size]The other impact will be the LPF set point.  As the corner frequency is brought in there will be more phase and amplitude imbalance as the corner frequency is approached. This phenomenon is typically consistent over frequency, but as a test the device can be put into bypass mode to see if there is a significant change. Maybe you already tried that.
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[/size]Best Regards,
[/size]Peter
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Hi Peter,
Thanks for the response.
I am not quite sure I understand how the balun affects the quadrature phase balance performance.  The balun is just used to take the single ended RF input and make it differential, correct? But the actual 90 degree phase splitting is inside the demodulator device, no? So shouldn't balance be a demodulator spec, rather than the balun?
Also, I looked at the balance plot on the balun and I am not sure I understand the plot.  I see a line that runs straight across the 180 degree mark and another line that straight across the 0 degree mark. How did you interpret the plot?

Regards,
Stan

Stan,


I might have misunderstood your question. I thought you was referring to the phase difference over frequency. In regards to the IQ imbalances, this sound indeed like a device specification, and this is the answer I copied from the TI design team"


"The typical image rejection performance for the TRF3711 is specified at 40 dBc.  The breakdown between phase imbalance and amplitude balance is not specified."


4DSP have no additional data on this.


Best regards,
Peter