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TRF370417 / output gain

Guru 19560 points

Hello,

In the datasheet figure 2 , TRF370417 output power @ 5.8GHz is about -7dBm.
And Vin 98mVrms is about -7.16dBm.(Please see the attached image as my calculation)
Thus, voltage gain is about 0dB.

However, Voltage gain @ fLO=5.8GHz is -5.5dB(typ).
Thus, there is discrepancy of gain.
Could you please let me know which gain should we use?
If my understanding is incorrect, please let me know.

Best Regards,
Ryuji Asaka

  • Ryuji:

    Please check out the following App Note: http://www.ti.com/lit/pdf/slwa056.  This App note specifically addressed the calculations used to determine gain.  I think the discrepancy above is related to SE vs. differential and/or the ideal combining power of the I/Q inputs in the modulator.

    --RJH

  • Guru 19560 points

    In reply to RJ Hopper:

    Hello RJH san,

    Thank you for your prompt reply.
    I understood.

    Best Regards,
    Ryuji Asaka

  • In reply to RJ Hopper:

    RJH,

    Looking at the app note and the example worked out in equations 1 through 3 the signal voltage at the input is listed as 0.1Vrms SE x 2. Is this indicating the differential voltage on a single I or Q input or is it meant to indicate that there is a 0.1Vrms SE voltage at each I and Q input? If the factor of 2 is to represent the differential signal level then is the presence of both I and Q signals implicit in the output power calculation?

    Thanks.

    Mark
  • In reply to Mark Whittington:

    I believe that the 0.1 Vrms SE voltage mentioned indicates that a 0.1 Vrms voltage is applied on both I and Q inputs and that the factor of 2 does indeed imply that the presence of I and Q are implicit in the output power calculation.

  • In reply to Abdallah Obidat:

    Abdallah,

    To be clear, in equation 1, the multiplication of the 0.1Vrms by a factor of 2 is to represent the fact that the 0.1Vrms single ended signal is present on both the I and the Q port and not to represent the actual differential voltage present on the I or Q (but not both) input, is that correct?

    If that is the case then i'm confused by the gain terms used in the TRF370417 datasheet.  As an example, at 2140MHz the gain is listed as -2.4dB and the gain is defined as the output rms voltage over the I (or Q) input rms voltage.  From that I would infer that the gain would be 3dB higher if I had both I and Q present.  But in the example worked from the app note, if my understanding per my first sentence is correct, then the gain when both I and Q are present is really -2.4 and there is a conflict between the app note and the data sheet.  

    Fundamentally I find the usage of the single ended voltage for differential inputs confusing since it isn't clear if I should truly be driving 0.2Vrms differential (equivalent of 0.1Vrms SE on each P/N input) or if I truly should drive the input with 0.1Vrms (either single ended or 0.05Vrms on each P/N input).  

    Thanks.

    Mark

  • In reply to Mark Whittington:

    Looking back at the block diagram in the datasheet, I see that both I and Q are provided as differential inputs. The datasheet and app note are consistent and correct. The factor of 2 is needed as 98mV is applied on the P and N inputs. 

    Mark Whittington

    Fundamentally I find the usage of the single ended voltage for differential inputs confusing since it isn't clear if I should truly be driving 0.2Vrms differential (equivalent of 0.1Vrms SE on each P/N input) or if I truly should drive the input with 0.1Vrms (either single ended or 0.05Vrms on each P/N input).  

    In this case you should drive the input with .1Vrms on each pin.

    Regards,

    Abdallah

  • In reply to Abdallah Obidat:

    Abdallah,

    I think you are now telling me that equation 1 in the app note is indicating a differential voltage of 0.2Vrms (0.1Vrms on the P input and 0.1Vrms on the N input). The voltage gain derived (-2.4dB) is the same as in the TRF 370417 datasheet at the same frequency where it explicitly states that the gain number is Output rms voltage over input I (or Q) rms voltage. But the figure used to find the output power, I think, is based on both I and Q inputs being loaded with the 0.1Vrms SE.

    I guess I'm just confused as to why the gain of the device defined as the dBV at a single I or Q input to the dBV of the combined I and Q power at the output. Or am I still confused?

    Thanks.

    Mark
  • In reply to Mark Whittington:

    I apologize if my initial response caused confusion. I didn’t initially realize that the inputs to the TRF370417 were differential. I can confirm that the equation is for a single channel, I or Q, but not both. The datasheet specifically states that “VinBB = 98 mVrms single-ended sine wave in quadrature”, which leads me to believe that the figure used to find the output power is based on Q alone. 

  • In reply to Abdallah Obidat:

    Abdallah,

    Just to repeat back to you so that I can confirm my understanding:

    The datasheet indicates ~0.1Vrms single ended voltage which is present on both P and N inputs applied to only one of the I or Q ports.  For an analysis that uses both I and Q inputs  the output power would be 3dB higher.

    Do I have it right?

    Thanks.

    Mark

  • In reply to Mark Whittington:

    Yes that is correct.