Re: [SI-LIST] : High Permittivity Board Level Decoupling and related issues

Elya B. Joffe (ebj@netvision.net.il)
Mon, 15 Jun 1998 21:58:39 +2

Dear Members,

a) High Permittivity Dielectrics

We are considering to use, for RF and ultra-high speed digital circuits, very
high permittivity dielectrics between the PCBs ("Thick Film FODEL").

Assume a separation between GND and VCC of 1.6mil, and a dielectric
constant Epsilon(r) of 5,000.

We have calculated that for a sq. Inch of PCB this is "worth" about 700nF of
decoupling.

In this case, would discrete decoupling capacitors actually be necessary,
would they be of any avail or perhaps even the opposite? Any input on this will
be greatly appreciated.

b) Analog Circuit Decoupling

Does anyone know any "rule of thumb" for selecting the proper value of
decoupling capacitors for <underline>analog circuits</underline>? In digital circuits - the rise time and
switching currents of the devices play an important role... What are the
considerations in Analog circuits???

Any reply to either or both questions will be greatly appreciated.

Thanks alot,

Elya B. Joffe - EMC Engineer

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