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LMX2594: Output power too low

Amy Luo
Expert 6895 points
Part Number: LMX2594

Hi team,

LMX2594 in the low frequency band, such as 2GHz, the output power is as low as - 70dBm, and the register loses control over the output power. The specific performance is : at first, the output is at high power, and the actual result is - 70dBm; Change to the medium power output, and the measurement result after startup is still - 70dBm; Change to the minimum power output, and the measurement result is still - 70dBm. The output frequency is normal.

The board basically refers to the EVM board, but it is only a double-layer board. The impedance or PCB wiring problem can be eliminated. Is it thermal protection or what reason？

Best Regards,

Amy Luo

  • 0
    TI__Guru** 108130 points

    Hi Amy,

    Is the problem only happen at 2GHz? What is the output power if the output is 8GHz or 100MHz?

  • 0 in reply to Noel Fung
    TI__Expert 6895 points

    Hi Noel,

    The customer's feedback is as follows

    The output power measured at 400MHz is still so low, and the PCB routing problem will not be so greatly attenuated. I wrote the program myself, and the register value is generated according to the relevant software. Should these pins be set to zero or one, such as sysref, rampclk and sync. If you have a development board, can you see if you can reproduce this problem. The above is the schematic diagram of the verification board.

  • 0 in reply to Amy Luo
    TI__Guru** 108130 points

    Hi Amy,

    the used pins can be left floating. 

    The reference clock connection is not correct. Remove R4 and make R2 = 0Ω.

    When they program the device, make sure program it in descending order. That is, the last register to program is R0.