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VCO noise - update
Thanks to everyone who replied. I've now discovered the reason for the
disastrous noise on the Mini-Circuits VCO: Obviously I was using *extremely* good RF PCB design techniques/layout, but these devices need even better than the very best. They are abnormally sensitive - not so much to noise on Vtune (20V tuning devices are less sensitive than the 5V wideband types) - but to earthing - much more than normal - and much more than Mini-Circuits own suggested PCB layout for the device suggests. And despite the fact that the tiny metal can is mostly directly bonded earth pins. It's not feasible how bad the results can be, even on a very good RF board! Apparently, the quoted -75dBc phase noise figure is almost unattainable, except using Mini-Circuits own metal block test jig. I've spent a week questioning myself and my Analyzer, so I hope this might help others to get acceptable results using this device. Use vias everywhere, solder the can all round, really go over-the-top on everything, in addition to all the normal RF grounding/decoupling practices, and then you might just get barely acceptable results. Al. --- |
The problem is the tuning voltage, and how sensitive it is. This applies to
all wide-range VCO's. I can't find the original message, but here's an example... Assume VCO tunes 1GHz to 2 GHZ with 20 volts of tuning voltage. While the tuning voltage is not linear, simply to linear assumption. Then the sensitivity of the tuning line is 1 GHz / 20 volts, this is the same as 1 KHz / 20 microvolts. It's really hard to get noise levels that low! Practically, the entire VCO as well as the circuit that drives the tuning line and all the componenets therein have to be inside a well shielded enclosure. Further, extraordinary care has to be taken in grounding. This means figuring out all the noise sources, ground return paths, etc. You cannot just hook everything to a groundplane, that's nowhere near good enough. It's necessary to group 'vias' to the ground plane based on which return currents they share, and then wire each ground connection or group of connections to the exact specific via needed. One cm of groundplane can have millivolts of potential difference across it. -- Tom "Alex Collins" wrote in message ... Thanks to everyone who replied. I've now discovered the reason for the disastrous noise on the Mini-Circuits VCO: Obviously I was using *extremely* good RF PCB design techniques/layout, but these devices need even better than the very best. They are abnormally sensitive - not so much to noise on Vtune (20V tuning devices are less sensitive than the 5V wideband types) - but to earthing - much more than normal - and much more than Mini-Circuits own suggested PCB layout for the device suggests. And despite the fact that the tiny metal can is mostly directly bonded earth pins. It's not feasible how bad the results can be, even on a very good RF board! Apparently, the quoted -75dBc phase noise figure is almost unattainable, except using Mini-Circuits own metal block test jig. I've spent a week questioning myself and my Analyzer, so I hope this might help others to get acceptable results using this device. Use vias everywhere, solder the can all round, really go over-the-top on everything, in addition to all the normal RF grounding/decoupling practices, and then you might just get barely acceptable results. Al. --- |
The problem is the tuning voltage, and how sensitive it is. This applies to
all wide-range VCO's. I can't find the original message, but here's an example... Assume VCO tunes 1GHz to 2 GHZ with 20 volts of tuning voltage. While the tuning voltage is not linear, simply to linear assumption. Then the sensitivity of the tuning line is 1 GHz / 20 volts, this is the same as 1 KHz / 20 microvolts. It's really hard to get noise levels that low! Practically, the entire VCO as well as the circuit that drives the tuning line and all the componenets therein have to be inside a well shielded enclosure. Further, extraordinary care has to be taken in grounding. This means figuring out all the noise sources, ground return paths, etc. You cannot just hook everything to a groundplane, that's nowhere near good enough. It's necessary to group 'vias' to the ground plane based on which return currents they share, and then wire each ground connection or group of connections to the exact specific via needed. One cm of groundplane can have millivolts of potential difference across it. -- Tom "Alex Collins" wrote in message ... Thanks to everyone who replied. I've now discovered the reason for the disastrous noise on the Mini-Circuits VCO: Obviously I was using *extremely* good RF PCB design techniques/layout, but these devices need even better than the very best. They are abnormally sensitive - not so much to noise on Vtune (20V tuning devices are less sensitive than the 5V wideband types) - but to earthing - much more than normal - and much more than Mini-Circuits own suggested PCB layout for the device suggests. And despite the fact that the tiny metal can is mostly directly bonded earth pins. It's not feasible how bad the results can be, even on a very good RF board! Apparently, the quoted -75dBc phase noise figure is almost unattainable, except using Mini-Circuits own metal block test jig. I've spent a week questioning myself and my Analyzer, so I hope this might help others to get acceptable results using this device. Use vias everywhere, solder the can all round, really go over-the-top on everything, in addition to all the normal RF grounding/decoupling practices, and then you might just get barely acceptable results. Al. --- |
In article , says...
Thanks to everyone who replied. I've now discovered the reason for the disastrous noise on the Mini-Circuits VCO: Obviously I was using *extremely* good RF PCB design techniques/layout, but these devices need even better than the very best. They are abnormally sensitive - not so much to noise on Vtune (20V tuning devices are less sensitive than the 5V wideband types) - but to earthing - much more than normal - and much more than Mini-Circuits own suggested PCB layout for the device suggests. And despite the fact that the tiny metal can is mostly directly bonded earth pins. It's not feasible how bad the results can be, even on a very good RF board! Apparently, the quoted -75dBc phase noise figure is almost unattainable, except using Mini-Circuits own metal block test jig. Did you read my post about phase-locking it at a low loop bandwidth before trying to measure PN? I've spent a week questioning myself and my Analyzer, so I hope this might help others to get acceptable results using this device. Use vias everywhere, solder the can all round, really go over-the-top on everything, in addition to all the normal RF grounding/decoupling practices, and then you might just get barely acceptable results. I don't think measuring -75 dBc/Hz at 1 kHz requires superhuman effort. It does require an understanding of the measurement process and the nature of the device being characterized, though. -- jm ------------------------------------------------------ http://www.qsl.net/ke5fx Note: My E-mail address has been altered to avoid spam ------------------------------------------------------ |
On Fri, 7 May 2004 07:55:14 +0100, "Alex Collins" wrote:
Thanks to everyone who replied. I've now discovered the reason for the disastrous noise on the Mini-Circuits VCO: Obviously I was using *extremely* good RF PCB design techniques/layout, but these devices need even better than the very best. They are abnormally sensitive - not so much to noise on Vtune (20V tuning devices are less sensitive than the 5V wideband types) - but to earthing - much more than normal - and much more than Mini-Circuits own suggested PCB layout for the device suggests. And despite the fact that the tiny metal can is mostly directly bonded earth pins. It's not feasible how bad the results can be, even on a very good RF board! Apparently, the quoted -75dBc phase noise figure is almost unattainable, except using Mini-Circuits own metal block test jig. I've spent a week questioning myself and my Analyzer, so I hope this might help others to get acceptable results using this device. Use vias everywhere, solder the can all round, really go over-the-top on everything, in addition to all the normal RF grounding/decoupling practices, and then you might just get barely acceptable results. Al. --- Could be the analyzer is noisey... Try measuring additive phase noise with two VCOs at the same time using a phase shifter to calculate the detector constant. subtract 3dB from your measurement. Remove "HeadFromButt", before replying by email. |
On Fri, 7 May 2004 07:55:14 +0100, "Alex Collins" wrote:
Thanks to everyone who replied. I've now discovered the reason for the disastrous noise on the Mini-Circuits VCO: Obviously I was using *extremely* good RF PCB design techniques/layout, but these devices need even better than the very best. They are abnormally sensitive - not so much to noise on Vtune (20V tuning devices are less sensitive than the 5V wideband types) - but to earthing - much more than normal - and much more than Mini-Circuits own suggested PCB layout for the device suggests. And despite the fact that the tiny metal can is mostly directly bonded earth pins. It's not feasible how bad the results can be, even on a very good RF board! Apparently, the quoted -75dBc phase noise figure is almost unattainable, except using Mini-Circuits own metal block test jig. I've spent a week questioning myself and my Analyzer, so I hope this might help others to get acceptable results using this device. Use vias everywhere, solder the can all round, really go over-the-top on everything, in addition to all the normal RF grounding/decoupling practices, and then you might just get barely acceptable results. Al. --- Could be the analyzer is noisey... Try measuring additive phase noise with two VCOs at the same time using a phase shifter to calculate the detector constant. subtract 3dB from your measurement. Remove "HeadFromButt", before replying by email. |
On Fri, 07 May 2004 22:02:42 GMT, eatitcold wrote:
On Fri, 7 May 2004 07:55:14 +0100, "Alex Collins" wrote: Thanks to everyone who replied. I've now discovered the reason for the disastrous noise on the Mini-Circuits VCO: Obviously I was using *extremely* good RF PCB design techniques/layout, but these devices need even better than the very best. They are abnormally sensitive - not so much to noise on Vtune (20V tuning devices are less sensitive than the 5V wideband types) - but to earthing - much more than normal - and much more than Mini-Circuits own suggested PCB layout for the device suggests. And despite the fact that the tiny metal can is mostly directly bonded earth pins. It's not feasible how bad the results can be, even on a very good RF board! Apparently, the quoted -75dBc phase noise figure is almost unattainable, except using Mini-Circuits own metal block test jig. A place I worked at years ago had nightmare probs with VCO phase noise. It depended on which freqs we were using though ( Z-Comm), some were ok, others..yeesh! Always had to have them in a can with soldered tops & undersides, shielding everywhere, & filters , filters, filters :-) newbies... Improving VCO Phase Noise Performance Through Enhanced Characterization http://www.highfrequencyelectronics....FE0104_Vye.pdf Remove "HeadFromButt", before replying by email. |
On Fri, 07 May 2004 22:02:42 GMT, eatitcold wrote:
On Fri, 7 May 2004 07:55:14 +0100, "Alex Collins" wrote: Thanks to everyone who replied. I've now discovered the reason for the disastrous noise on the Mini-Circuits VCO: Obviously I was using *extremely* good RF PCB design techniques/layout, but these devices need even better than the very best. They are abnormally sensitive - not so much to noise on Vtune (20V tuning devices are less sensitive than the 5V wideband types) - but to earthing - much more than normal - and much more than Mini-Circuits own suggested PCB layout for the device suggests. And despite the fact that the tiny metal can is mostly directly bonded earth pins. It's not feasible how bad the results can be, even on a very good RF board! Apparently, the quoted -75dBc phase noise figure is almost unattainable, except using Mini-Circuits own metal block test jig. A place I worked at years ago had nightmare probs with VCO phase noise. It depended on which freqs we were using though ( Z-Comm), some were ok, others..yeesh! Always had to have them in a can with soldered tops & undersides, shielding everywhere, & filters , filters, filters :-) newbies... Improving VCO Phase Noise Performance Through Enhanced Characterization http://www.highfrequencyelectronics....FE0104_Vye.pdf Remove "HeadFromButt", before replying by email. |
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