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I am a testing a high power amplifier IC(RF6886) for its s-parameters(gain and impedance matching) at a frequency of 145MHz. I have designed the board using eagle for this IC and got it manufactured through power PCB. The IC operates on a DC supply of 3.3V.

When I give supply to the board without connecting the vector network analyser, the IC draws a current of 0.3A and when I then connect the VNA, the current consumption increases to 0.9A and the supply voltage is observed to drop to 2.9V. Also, the VNA shows the gain as -15dB though the gain in dB of any amplifier should be positive. I have ensured multiple times that the IC and all the DC components as well the RF components have been soldered perfectly. What could be the cause for this to happen?

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    \$\begingroup\$ Add a schematic, a capture of the VNA traces, and a picture of the test set-up, including how are you biasing the amp. \$\endgroup\$ – Enric Blanco Apr 4 '17 at 10:49
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    \$\begingroup\$ And the layout of the PCB where the amp is mounted. \$\endgroup\$ – Enric Blanco Apr 4 '17 at 10:55
  • \$\begingroup\$ My problem got solved, now the VNA is showing positive gain. I soldered a new IC and also resoldered all the RF components which worked. Thanks for all the help. \$\endgroup\$ – Niramay Vaidya Apr 5 '17 at 12:57
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Some possibilities:

  1. Your analyzer has low impedance, and is significantly loading the output of the amplifier.

  2. You are connecting the two ports up wrong. Somehow the output is being shorted or partially shorted, perhaps due to incorrect common ground connection with the analyzer.

  3. Because of either of the above, the supply is partially collapsing, the power voltage is below spec, so of course there is no guarantee any more what the chip might do.

Check the datasheet and see if 900 mA is ever a valid current draw value. If not, then you are probably shorting the output somehow. If it is, then fix the power supply design so that the chip gets the right voltage over the full current range.

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  • \$\begingroup\$ The connections of VNA with the board are such that RF IN for port 1 and RF OUT for port 2 and in this case the S21 is coming -15dB. \$\endgroup\$ – Niramay Vaidya Apr 4 '17 at 13:41
  • \$\begingroup\$ The IC is capable of drawing 0.9A since it can draw a maximun of 3.1A from the supply. \$\endgroup\$ – Niramay Vaidya Apr 4 '17 at 13:42
  • \$\begingroup\$ @Niramay Is your supply capable of providing 3.1 A? \$\endgroup\$ – The Photon Apr 4 '17 at 14:33
  • \$\begingroup\$ Yes, my supply is capable of providing that current. Anyways, my problem got solved, now the VNA is showing positive gain. I soldered a new IC and also resoldered all the RF components which worked. Thanks for all the help. \$\endgroup\$ – Niramay Vaidya Apr 5 '17 at 12:58

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