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TRF3705: OIP3 performance

Lilian Chang
Intellectual 1555 points
Part Number: TRF3705
Other Parts Discussed in Thread: DAC34H84, DAC38J84

Hi team,

My customer have few questions about TRF3705:

1. the OIP3 data in our datasheet is SCL(single carrier level ) or DCL

2. Can they optimize sideband suppression by adjusting the common-mode voltage?

3. Will the different input baseband freq(i.e compare 350M and 630M) have different effect on the OIP3, gain, LO leakage and sideband suppression of the output signal?

Thank you.

 

  • 0
    TI__Guru 69354 points

    Hi Lilian,

    Let us investigate this and get back to you.

    -Kang

  • 0
    TI__Guru 69354 points

    Hi Lilian,

    for your questions, one clarification is needed:

    1. The OIP3 data is measured with two tones and back calculated from IMD3 performance. There are two tones on a single sideband carrier fashion.

    I believe you are asking whether the set up is single carrier or dual carrier setup. Since the TRF3705 is meant to be a I/Q modulator, the setup is always single carrier setup with suppressed image carrier. Dual carrier setup is typically a straight mixer with both the primary carrier and image associated with the output.

    Regarding your other two questions:

    2. Sideband suppression will have to be adjusted through I/Q gain/phase mismatch. Adjusting the differential common mode on I and Q will only result in LO leakage suppression.

    3. The datasheet does not supply the data of OIP3/LO leakage/sideband suppression vs. baseband frequency. Please let me know offline if it is critical.

    This setup will have to be done with a typical DAC setup like the DAC34H84 or DAC38j84. When the input baseband goes beyond the typical 50MHz range, the OIP3 of the DAC + TRF is limited not by the TRF, but the inherent DAC IMD3 performance at high frequency. You may see on the DAC datasheet that the IMD3 performance will degrade before the TRF degrades the input OIP3. 

    LO suppression is typically not a function of the frequency, but rather differential DC offset between I and Q.

    Sideband suppression, if the bandwidth is sufficiently narrow like 20MHz or so, is primarily driven by gain/phase mismatch of the I/Q data. If the bandwidth is sufficiently large like greater than 200MHz or so, then the group delay within the bandwidth of the carrier will impact the I/Q image suppression. Phase variation within the bandwidth will be function of @ = w*T where @ is the phase delta, w is the frequency, and T is the group delay between I and Q. In this case, the DAC38J84 has group delay compensation to compensate for such delta across the bandwidth. Also, when the baseband frequency is sufficiently high, both the LO and image can be filtered out easier, perhaps it is no longer an issue in such high IF applications.