AD9171 design issue

Hello,

Just want to ask the AD9171 design issue as below:

1. Datashee page 56 showed below info, if can help to explain the following formula in detail:

The ac differential current measured at DACx+ and DACx− is as follows:

IAC_DIFF (mA) = DACCODE/DACCODEMAX × IOUTFS × RINT(RLOAD + RINT)

where: DACCODE = 0 to 65,535 (decimal).

RLOAD is the load impedance seen on DACx+ and DACx−.

2. How to calculate the AD9171 output power?

Thanks a lot.

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  • 1. I believe the formula is not exact.

    Let me give one example.

    DACCODE is 2's complementary code:

    When DAC code = 32767, the differential current = 32767/32768 x IOUTFS x RINT (RLOAD + RINT)

    When DAC code = 0 the differential current = 0/32768 x IOUTFS x RINT (RLOAD + RINT)

    When DAC code = -32768, the differential current = -32768/32768 x IOUTFS x RINT (RLOAD + RINT)

    2. Output power = I^2 x RLOAD. For example, for a full scale sine digital code, the RMS power on load of 100Ohm with 20mA full scale settings will be = ~1dBm.

Reply
  • 1. I believe the formula is not exact.

    Let me give one example.

    DACCODE is 2's complementary code:

    When DAC code = 32767, the differential current = 32767/32768 x IOUTFS x RINT (RLOAD + RINT)

    When DAC code = 0 the differential current = 0/32768 x IOUTFS x RINT (RLOAD + RINT)

    When DAC code = -32768, the differential current = -32768/32768 x IOUTFS x RINT (RLOAD + RINT)

    2. Output power = I^2 x RLOAD. For example, for a full scale sine digital code, the RMS power on load of 100Ohm with 20mA full scale settings will be = ~1dBm.

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