Hi The real question is: Do you have an application where < 100 ps matching matters? If so do you need to match both at the amplifier *and* at the ends of the cables?
Other than a phased array radar, I can’t think of to many situations where the answer is yes … Put another way, for the normal stuff we do, it is not a significant issue. If you know the offset you can take it out in any calculations where it might matter. Bob > On Jan 28, 2017, at 6:58 AM, Anders Wallin <anders.e.e.wal...@gmail.com> > wrote: > > Hi all, > I've been tinkering with another distribution amplifier design and made > some measurements earlier this week. > The goal is roughly 1:8 fan-out, gain of 0 dB, for good quality (Cs, maser, > OCXO) 5 or 10 MHz signals in the range of maybe +0 dBm to +15 dBm - in a 1U > form-factor. > > Earlier I made an SMD version of the TADD-1 design [1] which showed about > -156 dBc/Hz far-out phase-noise but was quite sensitive to external noise > and required 12VDC power from a lead-acid battery as well as shielding in > aluminium foil for a 'quiet' PN-spectrum. > I then did some SPICE simulations [2] (never trust them without testing ;) > which indicated ADA4899 would be a good op-amp. In practice the > slew-rate/distortion was limiting and the AD4899 version didn't show better > PN. > > This new version is inspired by looking inside a 6502[3] - and in the > mean-time I also measured and Ettus Octoclock [4] - but its performance > isn't so exciting.. > > My current design is now here: https://goo.gl/photos/WB8fYd4jzba7nXH18 > So far my observations are: > - phase noise around -162 dBc/Hz at 10 MHz > - nice quiet PN-spectrum when unshielded and powered from lab-supplies > - this probably means the supply-section with common-mode choke, BNX025 > filter and LT1963/LT3015 is working OK. I should probably build a > 10Hz-100kHz LNA (e.g. [5]) to verify. I've used 2k@100MHz ferrites a lot > and an RC-filter on all supply pins - maybe overkill? > - an undesired feature is gain-peaking which increases from output ch1 to > ch8, shown here: https://goo.gl/photos/6QkoKakSPDdT7Acj7 > I tried to improve it a bit by adding a 100pF cap at the start of the long > trace that feeds the output stages, but some gain-peaking still remains: > https://goo.gl/photos/qrkLzZ21ptcHxFsw6 > - reverse isolation around 120 dB > - channel-to-channel isolation around 80 dB > - at 10MHz 1dB compression between +14 and +15 dBm > - IP3 perhaps +27dBm to +30 dBm. > > Any ideas on how to deal with the long 'feeder-trace' that seems to be the > cause of the gain-peaking? > Anyway if not used at 100MHz perhaps my next version will have reduced BW > where the feeder-trace is not an issue.. > Another issue is that the voltage regulators get quite hot when fed at > +/-12V and producing +/-6V. They should probably be positioned as far away > from the input/output amps and thermally disconnected if possible. I have a > +/-12V AC/DC brick on order - but a DIY linear PSU producing e.g. +/-8VDC > for the regulators might be better. > > The picture gallery also shows a pulse distribution amp for 1PPS. It has an > LT1711 comparator feeding an 74AC14 buffer with length-matched traces to > 74AC04's at the outputs. So far my length-matching didn't give zero > output-skew between the outputs - I see around 150-200ps skew which I tried > to tune a bit with wires and 0R resistors - without very much success.. any > ideas for improving this - or just leave it at 200ps skew? > > cheers, > Anders > > [1] > http://www.anderswallin.net/2015/12/frequency-distribution-amplifier-first-tests/ > [2] > http://www.anderswallin.net/2015/12/frequency-distribution-amplifier-v2-simulations/ > [3] > http://www.anderswallin.net/2016/02/symmetricom-6502-distribution-amplifier/ > [4] > http://www.anderswallin.net/2016/09/ettus-octoclock-distribution-amplifier/ > [5] http://cds.linear.com/docs/en/application-note/an83f.pdf > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.