## [SI-LIST] Answer for how to couple noise to the PDN of oscillator----Thank you all for the help and the discussion

• From: Zhangkun <zhang_kun@xxxxxxxxxx>
• To: si-list@xxxxxxxxxxxxx
• Date: Fri, 16 May 2008 16:14:47 +0800

Dear all:

Based on the talk about how to couple noise to the PDN of oscillator. I have
gotten several solutions:

1. Do not consider the dis-match
1) Connect the signal to the PDN directly
2) Measure the coupled noise on the PDN
3) Calculate the ratio between the noise and the jitter

2. By means of 1:N transformer to lessen the dis-match.

3. By means of other IC, creat a noise source with low impedance.

4. By means of opamp, which is of low impedance.

5. Because the low impedance of oscillator PDN is capacitive, there
would be a parallel resonance with a inductor(serial with a resistor).

Hope this would be helpful. Thank you for the discussion.

Original question:

Now we are studying the effect of power noise on jitter. We meet a problem,
how to couple noise to the PDN. For example, we want to couple noise of
25MHz into the PDN of oscillator. However there is impedance dismatch. The
impedance of signal source is about 50ohm and that of PDN is about 0.1ohm.
The energy would be reflected.

Best Regards

Zhangkun
2008.5.16

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