PLL, VCO and voltage regulation

[emax0198]

regulate vco supply

How the power supply for the sensitive PLL frequency synthesizer (MC145170) and the receiver circuit (MC3362, including VCO) can be separated from the rest of the circuit which might include microcontrolller, other digital circuit and servo motors?

Could two different voltage regulators can do the job connected from the same battery? How these 4V regulators can be completely isolated from each, connected to a same 4 cell rechargeable battery?

 

[IanP]

psrr vco

You can use RF inductors (≈1-10µH) on both on +V and GND together with some capacitors (100p + 100n + 100µ) and place the RF circuit in a shielded box ..

 

[emax0198]

vco voltage regulation nosie supply

What will be the noise performance by using ultra-low noise, low dropout voltage regulator(s) for the PLL circuit? How can I separate the Analog (Rx and PLL) ground from the digital ground?

 

[toonafishy]

vco psrr

Seperate regulators are a good way to isolate. You can keep the analog and the digital ground planes seperate and only connect them at one common point.

 

[emax0198]

Seperate regulators are a good way to isolate. You can keep the analog and the digital ground planes seperate and only connect them at one common point.

But the ground remains common to both the regulators!!

 

[toonafishy]

It works quite well. It is the standard way to connect analog and digital grounds.

 

[emax0198]

How about placing LC Low pass filters with high inductance between the 2 regulators for both +ve and ground supply lines? No doubt they will impose a voltage drop!

 

[coronado]

you can put separate regulators

 

[eecly]

A good voltage regulator is a must for a PLL or VCO circuit. Pushing effect is obvious if the voltage supply is unstable.

In addition, decoupling capacitor is also important for further noise supression. Either in input or output of voltage regulator.

 

[No one]

Hello;
Can anyone provide links and/or PDF documents about this problem?
Thanks.
No one

 

[layes2]

vco need psrr so regulator is used

 

[itaifrenkel]

emax0198 -

Remember that the noise in high frequencies can propagates between two parallel plates. So a common GND cannot bring the noise from the digital circuits to the analog circuits. If however, you use the common GND and VDD plates then high frequency noise can propagate between the plates even from one side of the board to the other.

There are dedicated simulation tools for "ground bounce" and resonances (such as Ansoft SIwave). This simulation tool allows you to simulate your board's power planes including the lumped (R,L,C) elements and measure the isolation between the digital and analog power planes.

Regards,
Itai Frenkel

 

[No one]

Hello;
itaifrenkel wrote:

There are dedicated simulation tools for "ground bounce" and resonances (such as Ansoft SIwave). This simulation tool allows you to simulate your board's power planes including the lumped (R,L,C) elements and measure the isolation between the digital and analog power planes.

Can anyone explain more with example?