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LTC5599 input level versus digital gain setting.


The LTC5599 datasheet states that the maximum input swing without hard clipping is typical 1.2Vpp at Digital gain setting -10. (Page 4 of the datasheet).

My question is how the digital gain setting and the maximum input voltage swing correspond. This was not entirely clear from the datasheet.

Kind regards, Pim Swinkels

  • The LTC5599 was not fully characterized for maximum input swing vs gain setting. However, from plot G90 on page 16 of the datasheet, you can estimate input voltage swing for some gain settings.

    For example, at 500MHz RF output frequency, when DG=-19, the 1% RMS EVM level is at about -10dBm RF output power, which is 0.10Vp. DG=-19 sets the effect gain of the demodulator to about -22.7dB. (Per LTC5599 datasheet, default DG=-4 and gain is -7.7dB.) Vin(diff) = Vout / [10^(gain/20)] = 0.10/[10^(-22.7/20)] = 1.36Vp = 2.72Vpp. So on each baseband pins, the maximum Vswing = 1.36Vpp.

    A simpler equation is:

    Vswing_pp = 10 ^ [ ( Pout_dBm - gain - 10 ) / 20 ]

    One more example: default settings (DG=-4,gain=-7.7dB), 1% RMS EVM is at 0dBm output power. Vswing = 10^[(0+7.7-10)/20] = 0.77Vpp