Decoupling circuit IC
I want to mount a mmic GaAs amplifier operating at 30GHz on a board with a heat sink. The DC power supply will be connected to the die through a decoupling circuit composed of bonding wires/resistors and capacitors.
The drain voltage is 7V.
Can anyone help me to make a decision about the proper decoupling circuit ?
How to size the capacitor value ?
Should I use different capacitor values ?
Thank you
Check manufacturer's data for the advice you need. Or find a similar commercial MMIC die and instructions for it.
microwave 1pF + COG/100pF/0402 + NPO/10nF/0603 + 10uF/16V/A case
Right at the device, I'd stick a 100 pF microwave cap (like AT Ceramic's single-layer caps, Microcaps, etc). Similar to Tony, I'd stick a COG 100 pF cap in the DC bias circuit, then something more "bulk" beyond that, at the power input point to the board... 1-10 nF, etc, and bigger uF parts beyond that, depending on your on/off transition-time requirements.
Look at the device's manufacturer's datasheet or app note. The manufacturer should give you a recommended circuit implementation, especially when it comes to the bypass cap configuration.
Thank you tony_lth, so using those values ensure a proper decoupling. Could you explain how did you do to get it ?
The impedance synthesized by this set of capacitors should be high in the operating frequency range? Right?
I don't understand your question? Do you mean the total cap is more than 10uF?
For decoupling caps, you want the impedance to be low, so the AC signals have a low impedance path to ground, and thus, back to their source. If you are operating at 30 GHz, then a 1 pF cap is Zc = 1/(jωC) = -j0.188 ohms. As C gets larger, the impedance gets smaller, which is what you want.