using decoupling capacities and beads

Please can you give some information about this issue?

- Which values of Caps must we put near the ICs in HI / LOw frequencies.?

- Which values of Caps must we put for board de-coupling ?

- Which values of Caps and L s (beads etc. ) must we use between Analog VCC and Digital VCC, also between Analog GND and Digital GND? in high and low frequencies?

for example, on a board that runs in 50 MHz, can i use 100nF for board de-coupling and 100nFs for ICs near VCC pins ? and what value of Bead can i use between the AVCC and DVCC ?

Thanks

Thats a very interesting question which involves lots of areas of electronics.
Good pcb layout is also required.

The manufacturers of iC's like processors, microcontrollers, ADC's sometimes give advise in the datasheet.

Typically for a noise sensitive IC like an ADC or an IC that can change current consuption rapidly
such as a uC or driver that can turn all it's pins on or off at once I would use a 2u2 tantalum
and a 100n ceramic in parallel.

>Which values of Caps must we put near the ICs in HI / LOw frequencies.?

It also depends on the current consumption of your circuit.
At low frequencys and low current it is not critical, no caps at all is bad for regulator
stability. Hundreds of uF makes the switch-on inrush current high.

>Which values of Caps and L s (beads etc. ) must we use between Analog VCC and
>Digital VCC, also between Analog GND and Digital GND? in high and low frequencies?

There is no simple answer to that. It must be considered along with board layout, number
of regulators, frequencys involved etc. There is a danger of capacitor self resonances
and resonances between L and C at high frequencys.

Best answer is to read High-Speed Digital Design: A Handbook of Black Magic by Howard Johnson

>on a board that runs in 50 MHz, can i use 100nF for board de-coupling and 100nFs for ICs near VCC pins ?

That will probably be ok at 50MHz. I assume you mean 100uF for board decoupling?

For more discussion see previous threads