Can you give some advice on suppress noise from regulator?

[Jeekoky]

I am designing a low phase noise crystal oscillator. The noise of the supply(need 9V and 10mA current) is critical! So i need to suppress the noise from regulaor to about 7nV/sqrt(Hz) noise floor(about 100 or 1k to 1MHz). The 723 regulaor output noise is about 20uV(from 100 to 10kHz). It's much larger noise than i need(equal to 0.7uV from 100 to 10kHz) . Can some one suggest some circuit to do these? How about noise clipper circuit?

 

[Humungus]

Re: Can you give some advice on suppress noise from regulato

The only way that you have, given that you have already chosen the voltage regulator, is to connect a big capacitor on the Vdd node. Remember that the spectral noise on the capacitor's terminals would be KT/C.

 

[Jeekoky]

Re: Can you give some advice on suppress noise from regulato

Big capacitor is not possible. Its will be at least several hundrd uF and i can't place it.
If suppress is impossible with brief circiuts, can I design a simple discrete transistor regulator to instead 723? I don't care about many things like the low differential voltage, accurate voltage value and low-temperature drift, which is required in monolithic voltage regulators. Where can i get such circuits to learn from?

 

[IanP]

Re: Can you give some advice on suppress noise from regulato

The 723 is still one of the best regulators ever known..
If you want to reduce "noice" would you consider using L-C tank at its output consisting of at least 1mH inductor and 100nF + 1/10/100µF capacitor combination ..

 

[Jeekoky]

I found a interest fact about NS LM723. The output noise from LM723 is well from 100Hz to 10KHz, but raised quickly above 10KHz. Finally at about 1MHz, the noise begin to go down again. So i recommend to use a large capacitance parallel with a smaller one to bypass the output of LM723.
About my question. I now still has no good idea. Maybe i need to construct a simple regulator with the best voltage reference and trasistor. Who know.

 

[mqc_hn]

Re: Can you give some advice on suppress noise from regulato

If include KT/C noise, correlated double sampling circuit can reduce it.