I'm trying to decide on a safe input power to a power amplifier. The amplifier in question is SE5004L. The datasheet specifies that the amplifier output 1-dB compression point has a minimum value of 30dBm and a typical value of 34dBm. The small-signal gain is 32dBm. Without making any further adjustments in my design, the input power to it would be -1dBm, putting the output power at about 31dBm. However, this is close to the 1-dB compression point and the datasheet specifies a 26dBm output power at 3% EVM. I have a 6dB attenuator that I can use, which would bring the output power about to the typical range in the datasheet. I'd like to get as much output power as possible, but not if it significantly distorts my signal. Is it generally ok to operate near the 1-dB compression point, or is it better to stay 5-10dBm below? This is for a FMCW radar operating at around 6GHz.

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    \$\begingroup\$ The answer on compression and rise in THD demands a design analysis of how harmonics create false images at 2x or 3 x the distance in the mixed baseband result from an increase in baseband noise. \$\endgroup\$ – Sunnyskyguy EE75 Dec 12 '18 at 3:16
  • \$\begingroup\$ Is your transmitter output JUST A SINE WAVE? no modulation, other than the FMSweep? \$\endgroup\$ – analogsystemsrf Dec 12 '18 at 4:39
  • \$\begingroup\$ @analogsystemsrf yeah that's right, no modulation, just a delay between each burst. The waveform is a sawtooth ramp in the frequency domain, 5.3GHz to 5.9GHz over 1ms, delay of 2ms, then repeat. \$\endgroup\$ – MattHusz Dec 12 '18 at 5:16

It all depends on how much distortion you can tolerate, and any other side effects that may occur when saturating the amplifier (harmonics, etc.). You might be fine running several dB over the P1dB point. Or maybe you need to stay several dB below. You might just need to experiment. If your FMCW radar can tolerate some distortion, then you might be able to hit it pretty hard. On the other hand, if you're using a digital modulation like high order QAM, you might need to stay well below the P1dB point.


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