HMC997LC4 & HMC943APM5E RF output issue

Hi,

We're using the HMC997LC4 VGA in series with the HMC943APM5E PA device (VGA used to pre-amp before the PA).

However, the power output at the PA is about 30dB lower than expected.

We can only get up to +1dBm on the output of the PA before it saturates.

We have tested the circuit at 23GHz (the PA is specified for 24GHz-34GHz, but we can see that the datasheet has curves starting from 23GHz, so we don't suspect this is an issue).

When at +1dBm output level, the control voltage of the VGA is -2V. When we decrease the voltage beyond that (to -2.1V), the output power actually decreases rather than increasing.

We measured the power rails of both the VGA and the PA on the oscilloscope and they were steady without any glitches/drops.

We also followed the biasing procedure for both devices (the PA biased at 1.1A and the VGA at 170mA)

What could be causing this? Are we doing anything fundamentally wrong?

We have seen the exact same behaviour on 2 PCBs.

Parents Reply Children