PLEASE HELP !!! :One LDO supplying voltage for two circuits

[ericz]

Hi all,

Can I use only one LDO that supplies current for two circuits (for example, the LDO will maintain the voltage for Amplifier and for PLL and VCO all together).

Is this concept is common or this is bad idea?

can anyone give me some links for such examples which are bad or good?

Thanks,

 

[flushrat]

Re: PLEASE HELP !!! :One LDO supplying voltage for two circu

LDO is to prevent noise from vco or pll going into power. If amp and vco share a LDO, noise from vco will greatly destroy amp.
In general, one ldo for vco, one ldo for otther parts of PLL(pfd, devider), another for amp.

 

[sunking]

add L&C may help you

 

[suria3]

Re: PLEASE HELP !!! :One LDO supplying voltage for two circu

It is possible to share the same LDO for the circuit but as mentioned by Flushrat, if the PLL and VCO contriute some of amount of noise which will affect other block of amplifers due to coupling, then it is advisable to have different LDO shared. Normally those blocks/amplifiers which operated in higher signal switching then they will have different LDO.

 

[IanP]

Re: PLEASE HELP !!! :One LDO supplying voltage for two circu

Decoupling
There are instances where the power distribution between stages cannot be sufficiency bypassed. In this case, the designer might be tempted to use several different power supplies. However, by supplying the DC power to each stage through a separate inductor or "choke," while also bypassing to ground that stage, the effect is the same. That is to say, the choke offers a high impedance path to any errant signals or noise between stages, while offering a very low resistance path to the DC power: this is known as decoupling. Active devices such as voltage regulators can also be used for decoupling stages.

In the rest of this section (DECOUPLING) you will find pros and cons on using active separation with voltage regulators or passive with LC ..

http://www.williamson-labs.com/480_byp.htm

Regards,
IanP