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HMC980 bias controller used with HMC608

I am using the HMC980 bias controller with the HMC608 amplifier.

The input power to the amplifier is 3 dBm.

The bias conditions are: Rset=510 ohm (Idrain=300mA) delivering to the amplifier VDrain=4.8V and VG= -3.2V.

We are using the amplifier in an FMCW application. The output of the amplifier appears to oscillate at particular frequencies over the sweep (9.5 - 9.7 GHz). When we lower the drain current (Rset=580ohm), the oscillation goes away. I don't know if the issue is related to the biasing IC or the amplifier.

At the moment I am suspecting that the amplifier is dissipating too much power and that causes some nonlinear behaviour (refer to power dissipation figure on page 3 of datasheet).

Any advice regarding this problem will be appreciated.

  • Hi,

    I think Idrain is set too low at this input drive since power amplifier's current tends to expand with higher output power. Since HMC980 is biasing the amplifier at a constant current, driving it at Pin = 3 dBm will likely saturate the amplifier causing nonlinearities. I recommend bias it at Idrain = 600 - 650mA since it is the current drawn under constant voltage biasing.