Regulator in PLL for VCO and charge pump

[crossroad]

I use a regulator to provide a regulated supply for VCO and charge pump. In charge pump, the regulated supply is seriously affected by the swtiching of charging/discharging (in a frequency of the reference clock). In VCO, it's polluted by the 2nd harmonic of the oscillation frequency. To solve this, is is the only way that adding a very large capacitor between the regulated supply and GND ??
Please help me!! Thx!!

 

[Vamsi Mocherla]

regulator in PLL

Firstly, the main reason why you want to have an isolated regulator is that you need to switching noise on the VCO as a VCO with high Kv gain is prone to a very high power supply sensitivity and adds jitter to the output. Remember that the VCO is high pass to noise transfer. Hence all the high frequency components are passed through which effect the output frequency of the VCO. Hence, the regulator normally is a linear type, LDO.

The reason why you are seeing a second harmonic is because the output impedance of the regulator is quite high. A good idea is to resize your pass transistor and then test your VCO. Adding an extra capacitor will help filter out the power supply ripple but that is an extra cost and real estate on the board.

 

[hung_wai_ming@hotmail.com]

regulator in PLL

I think you should not use one single regulator to supply power to charge pump and VCO and you should separate the two components with different power, othewise, you may get nothing improved

 

[neter]

regulator in PLL

So,PFD and Charge pump LPF VCO have separate power or individual LDO ?

 

[khouly]

regulator in PLL

the VCO , and the Charge pump , need to be separted

khouly