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Using HMC980 with HMC7357 Power Amp

Question asked by JSobtzak on Nov 14, 2016
Latest reply on Dec 2, 2016 by kkaya

I'd like to use the HMC980 to control the power on/off sequencing of my HMC7357 but I am not sure if I want the constant drain current feature of the HMC980 since the drain current can go as high as ~1350 mA.  The questions I have are:

 

1 - Is there a bias sequencer part that holds Vgg steady and lets Idd very with RF drive power?

2 - If I use the HMC980, what bias current do I set it to?   The datasheet is specified for an Idq of 1200 mA, but in the plots for power compression for the HMC7357 (pages 4-5 of datasheet) the drain current is not constant - implying that the device was tested under constant gate voltage.

 

My application is very sensitive to efficiency and linearity, so if I want to operate at 8 GHz and at the P1dB point, the power compression curve says drain current needs to be >1300 mA. 

 

What I really want is a constant gate voltage controller that provides the correct power sequencing for a GaAs pHEMT, such as the HMC7357, but I could not find one of those, and I'm hesitant to use an active controller that varies gate voltage to hold a steady drain current on a device that has been characterized under a constant gate voltage.

 

Any advice out there?

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