The Importance of low phase noise in ADC and DAC clocks

There are a couple of excellent articles on the effects of sample clock phase noise on DAC and ADC performance from Analog Devices.

Analyzing and Managing the Impact of Supply Noise and Clock Jitter on High Speed DAC Phase Noise

Sampled Systems and the Effects of Clock Phase Noise and Jitter.

Also another good paper from TI.

Why phase noise matters in RF sampling converters.

There is a trend in radio system design towards doing ever more of the signal processing in the digital domain. This has been enabled by DAC, ADC, and signal processing blocks, with ever faster sample rates, driven by the process shrinks as predicted by Moore’s Law. These process shrinks have also delivered lower power consumption making this design approach suitable for battery powered products and easing thermal design issues.

In all analogue radio designs, the phase noise of the local oscillator was key to radio performance. While this is still true of mixed analogue/digital designs, arguably the DAC/ADC clock has become just as important. When these clocks were in the 10s of MHz supplying a good quality clock was achieved by buying a good quality crystal oscillator. Now these clocks are in the 100s of MHz and GHz, achieving low phase noise and hence jitter is not so straight forward, as off-the-shelf crystal oscillators are only available up to about 100MHz. Beyond that oscillator modules use PLL based multipliers which inevitably add phase noise. At Golledge I have designed a 290MHz crystal oscillator using one of their high frequency fundamental mode resonators. Much above this, ultra low phase noise sources must look to other high Q resonators, such as SAW resonators. I hope to write more on this later.

Chaos in Radio

There is an interesting article in EETimes about chaotic oscillator circuits. It made me think of mobile radio groups where all members run AFC. Designers usually avoid using the receive AFC setting to adjust the transmit frequency, unless there is one known good node in the network that others can synchronise with. When all nodes are equal and transmit frequency is based on the last signal seen, then it has been assumed that the group as a whole will wander off frequency and also may split up. This work suggest there may be some cleaver alternatives.

Looking for papers for ARMMS.

I’m technical co-ordinator for the next conference of ARMMS. This involves recruiting presenters of technical papers of interest to RF and Microwave engineers and academic researchers. If you would like to present a paper please let me know.

November ARMMS

I’m programme co-ordinator for the next ARMMS conference. The job mainly consists of finding people to present technical papers at the conference. These have to be of specific interest to engineers ond researchers of a RF and microwave background. If you are interested in presenting a paper contact me.

Cahootify

This is an outfit I have been following since they launched a fund raising round on Seedrs. They are now trying again on Crowdcube. It seems just what is needed in the independent consulting world. They are based not to far from me as well.

New Domains

This site has grown a couple of aliases. You can now get here via my analogue.guru domain or the rfdesign.guru domain.
I’m pleased with getting these. They will help with self promotion and keeping Bayford Systems alive while I’m away working for Golledge Electronics. I can see why I got away with getting analogue.guru, The domain squatters would be using American dictionaries so not have squatted the English version. I am surprised no-one had bagged rfdesign though. It’s such an obvious choice. Perhaps the launch of the guru top level domain (TLD) has not been sufficiently high profile.