Hi, I'm considering using the HMC981 for controlling bias on the HMC996 VGA. I have a few questions:
1) Is this part compatible with the HMC996?
2) If the HMC981 controls two gate voltages, how come there is only one drain voltage input for current monitoring?
Isn't that doing bias control based on feedback from combined amplifier stage currents? I need to ensure that each
stage of amplification is getting the constant Idsq bias.
3) If used with HMC996, which Vgg pins get connected to Vgate, VG2 on HMC981 controller?
I assume Vgg1 to Vgate and Vgg2 to VG2, but it is not completely clear to me from the datasheet.
Thanks for resolving this confusion.
1. Yes. HMC980 is also compatible with more Idd and Igg capability.
2. You can connect Vdds together and Vggs together, like it is done to collect the data on the datasheet.
3. Connect Vgg1 and Vgg2 to each other. Then Connect Vgate output of HMC981 to those connected Vggs. Leave VG2 otput of HMC981 open. VG2 output is for cascode amplifiers that require a positive VG2 bias, like HMC46x.