Linear Regulator And Filtering

[ballimo]

Dear All,

I have 4 Crystal oscillators with a supply voltage of 3.3V; the output frequencies of these oscillator is : 155 MHz, 311 MHz , 644 MHz, 100 MHz.

I have used a Linear Regulator to supply the 3.3V for these oscillators; My question is:
should I use a ferrite bead for each VDD pin (supply voltage pin) of these oscillator? the linear regulator has a very low noise output voltage, so I guess a filtering is not needed, but do we need an isolation using a ferrite bead?

Thanks in advance,

Ballimo

 

[chuckey]

It depends on the DC filtering of the oscillators, with them related closely in harmonics, I would use feed through capacitors and proper little inductors as RF chokes (10 Turns around a 4mm former) and a ferrite bead.
Frank

 

[ballimo]

Thank you Frank for the answer,

By "DC filtering of the oscillators" do you mean DC filtering inside the oscillator package?

only 155MHz and 311 MHz are related closely in harmonics, please correct me if I am wrong; using a ferrite bead and feed through capacitors are only needed for these two oscillators, correct?

as circuit design adding 4 ferrite bead and cap for each of the oscillator is easy; my concern is the layout (during PCB routing): I will go from linear regulator on top of the PCB using "via" to the internal plan layer than to the ferrite bead on top using "via".. usually via should be avoided during power routing (inductance);
how much is adding ferrite bead is important in term of noise.

Regards,

Ballimo

 

[chuckey]

Ferrite beads do not add noise. Yes I was talking about the actual oscillators, which I presume are supplied in metal cans. See what the ferrite bead manufacturers spec says about their impedance.
Frank