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Design >> RF Design >> DCO Quantization Noise White Dithering
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Message started by neoflash on Jan 12^th, 2008, 6:56am

Title: DCO Quantization Noise White Dithering
Post by neoflash on Jan 12^th, 2008, 6:56am

Hi, Folks:

I'm reading some papers on DCO.

One question I got is on white dithering of DCO. Basically due to limited frequency resolution, there is high quantization noise without sigma-delta modulation. White dithering is often used in this case.

1. I'm not sure that white dithering is using finer resolution, i.e. smaller capacitor, for random dithering or not. For example, if dithering word length is 4-bit, can I say that dithering LSB resolution is 1/16 of normal control bits?

2. If it is using smaller capacitor, why not directly use that in normal control bits, to lower the quantization noise?

Thanks,
Neoflash

Title: Re: DCO Quantization Noise White Dithering
Post by chenyan on Feb 19^th, 2008, 5:10am

dithering of DCO should always be on the smallest varactor

Title: Re: DCO Quantization Noise White Dithering
Post by emad on Mar 5^th, 2008, 9:30pm

The idea is to have an infinitely small capacitance. The trick is to do that through time averaging of a larger cap. Of course this causes quantization noise and the smaller the dithered cap the lower the quantization noise.

Emad

Title: Re: DCO Quantization Noise White Dithering
Post by neoflash on Mar 6^th, 2008, 5:26am

emad wrote on Mar 5^th, 2008, 9:30pm:

Yes, then I think the LSB cap in both dithering and regular control bits should be the same in size.