Decoupling circuit IC

[jayce3390]

Hi,

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

 

[jiripolivka]

Check manufacturer's data for the advice you need. Or find a similar commercial MMIC die and instructions for it.

 

[tony_lth]

microwave 1pF + COG/100pF/0402 + NPO/10nF/0603 + 10uF/16V/A case

 

[enjunear]

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.

 

[jayce3390]

microwave 1pF + COG/100pF/0402 + NPO/10nF/0603 + 10uF/16V/A case

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?

 

[tony_lth]

The impedance synthesized by this set of capacitors should be high in ......

I don't understand your question? Do you mean the total cap is more than 10uF?

 

[enjunear]

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?

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.