capacitor for Q-band question

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yefj

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Hello , i have a capacitor which works in Q band its description is as follows.
CAP,10uF,+-20% ,50V, X5R , 1206.
There are many capacitor manufacturers,how do i pick a good component that will work in Q-band with these parameters?
Thanks.

 

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I think you need to forget about everything you listed and read up on
RF capacitors. ESR and ESL and how you place & route them. Linearity
interests want a zero voltco so dielectric mayb be none of the above
but a plain glass or no-funny-business dielectric.
 

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yefj said:
Hello Bigboss 30-40GHz
Click to expand...
Dear Mate,
You can NOT use this type of capacitors' in that frequency band. I recommend you to research "Capacitors' Behaviors" subject. This capacitor will behave as an Inductor with very high loss in that band. This is a simple and essential knowledge about them.
 

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It's also true that in that band, every bit of interconnect
matters as much as the component itself. Until you know
the circuit and its physical form you don't know what kind
of ESL in the cap itself is acceptable in the circuit context.
Like, why chase 10pH ESL when it's placed in a trace
that's 1nH end to end, and 50pH you couldn't tell the
difference (difference being, you can't -find- 10pH ESL...)?
 

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kingcrediepcba said:
Hi,

I think you can find in mouser's website.

part number is KGM31HR51H106MU or KGM31HR51H106ML.
Click to expand...
Hello, I have found the datasheet of this capacitor.
Indeed in 30GHz capacitor can turn into inductor.
I need to put it around the DIE as shown below.in the datasheet they dont say exactly which capacitor they used(as shown in the table below)
Is there some intuition that could help me know if the KGM31HR51H106MU could work at 30-40GHZ?
Thanks.



--- Updated ---

UPDATE:
Stupid mistake by me,its a decoupling capacitors. ash shown in the datasheet.
Its seems to be that i need a "simple" capacitor
correct me if i wrong.

 
Last edited:

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10uF Capacitor is used to reduce Low Frequency Ripples/Noises coming from Power Supply.
You have to use multiple capacitors in parallel to reduce ripples/noises coming from the power supply AND to tie the supply line to GND for almost every band. Therefore you should select appropriate capacitors for this purpose.
For instance;
10uF+10nF ( low frequency models are OK) then 100pF+10pF+1pF ( High Frequency, Low ESR, Low Inductance Microwave Type Capacitors )

This is just an example. You have to find proper values by Simulation+ Measurements.
Decoupling Capacitors play also on Nonlinearity of the Amplifier/System.
 

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Neither X5R 10uF nor X7R 100nF are dedicated microwave capacitors, nevertheless they have some bypass effect. The impedance at 30 GHz will be inductive and mostly defined by capacitor chip dimensions, no big differences between manufacturers expectable. In the shown layout, capacitor inductance is
most likely surpassed by trace inductance.

I don't fully understand how bypassing in the reference design is expected to work. The series resistors will cause a relative large AC voltage drop at 3 W output power if the shown capacitors are the only effective bypass means. May be operation depends on internal substrate capacitance of the amplifier chip.
 
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So it's not possible.
You have to find the right values by measurements( cut-and-try ). EVM Measurements may give you an idea.
But I agree with Fvm so the application board has some unusual techniques and I cannot see why..
 

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