[time-nuts] Using commercial video amplifier for 10MHz clock distribution.

[timeok at timeok.it]

   Charles wrote:
   >Well, there is a distinct difference between DAs that use a single
   amplifier (discrete or integrated) to drive each output channel (as your
   design does), and DAs that drive multiple outputs from each amplifier
   using build-out resistors. In the case of the Extron integrated circuit
   DAs using CLS409 opamps, the isolation is 30dB between outputs fed from
   one amplifier, and >90dB between outputs fed from different amplifiers
   (see my document detailing recommended modifications to the Extron DAs,
   downloadable from):
   <http://www.ko4bb.com/getsimple/index.php?id=download&file=02_GPS_Timing/Extron_ADA_6_modifications_for_use_as_10MHz_distribution_amp_STEINMETZ.pdf>
   So, simply by using only some of the outputs of an Extron IC-based DA,
   one gets isolation roughly equal to your design.


   < The solution I proposed is a 107dB channnel to channel isolation (gain set +3dB).



    > One advantage of the IC design is considerably lower distortion -- the
   harmonics are all below -65dBc at 10MHz, +16dBm output, compared to
   -45dBc at +13dBm for your design (per your table). Further, the
   distortion products of the IC design are essentially all odd-order
   harmonics, while your design shows predominant even-order harmonics.

   < The CLC409 datasheet show all the test response up to +12dBm (around 1Vpp on 75/50Ohm load)
    see: pdf.datasheetcatalog.com/datasheet/nationalsemiconductor/DS012748.PDF

   I agree that harmonic distortion is an important factor to keep in mind however -45dBc is a very interesting value considering the market alternatives. In my document I have enclosed on page 10 a little research I did online on similar products and as you can see the -45 are positioned at a decidedly higher level than other commercial solutions
   see:
   http://www.timeok.it/wp-content/uploads/2015/08/Frequency-Distribution-Design-Basic-Module-v-4.1.pdf

   An extremely important factor not to be overlooked is the maximum output power / level of the amplifier. Measurement systems such as the HP3048A for phase noise measurement use mixers that require minimum signal levels of + 15dBm at higher PO1 and the CLC409 will never meet these requirements.


   >In your modification document: Residual phase noise of <-165dBc at 10 MHz


   <I suppose you mean @100kHz, The buffer I propose is -170dBc @100KHz


   In a nutshell my desire was to have a very flexible circuit with high isolation, low harmonic distortion, very low phase noise high output level on 50 Ohm load, high input impedance, selectable gain in addition to having a low cost. Another factor was to be able to power it with single voltage using a linear voltage regulator to adapt to both the AC and 24VDC standards.


   In the end I don't think this should be a competition among Distribution Amplifiers. The Extron is undoubtedly an excellent solution and I must also say that it was very well made but I don't think it's a professional solution. Maybe mine isn't either; in reality mine is very little, the basic project is by Bruce Griffith to whom I made minor changes. This buffer has been used inside many HP5065A, HP10811 and Distribution Amplifier without problems and with great results.

   For a "ready" solution at low cost like DA the Extron I think is a great solution.



   Best regards,
   Luciano


   Da "time-nuts" time-nuts-bounces at lists.febo.com
   A time-nuts at lists.febo.com
   Cc
   Data Wed, 23 Oct 2019 07:25:20 -0400
   Oggetto Re: [time-nuts] Using commercial video amplifier for 10MHz clock distribution.
   Luciano wrote:

   > The Extron is a very nice solution, certainly of modest price, but we must consider * * * the low separation between the output channels.

   Well, there is a distinct difference between DAs that use a single
   amplifier (discrete or integrated) to drive each output channel (as your
   design does), and DAs that drive multiple outputs from each amplifier
   using build-out resistors. In the case of the Extron integrated circuit
   DAs using CLS409 opamps, the isolation is 30dB between outputs fed from
   one amplifier, and >90dB between outputs fed from different amplifiers
   (see my document detailing recommended modifications to the Extron DAs,
   downloadable from):

   <http://www.ko4bb.com/getsimple/index.php?id=download&file=02_GPS_Timing/Extron_ADA_6_modifications_for_use_as_10MHz_distribution_amp_STEINMETZ.pdf>

   So, simply by using only some of the outputs of an Extron IC-based DA,
   one gets isolation roughly equal to your design. Of course, one could
   easily build a one-output-per-amplifier DA using the Extron circuit
   (with LMH6702 or other suitable opamps) to have a DA with ~100 dB of
   isolation between all outputs (the exact isolation will be dependent
   upon the layout, just as it is with your design).

   One advantage of the IC design is considerably lower distortion -- the
   harmonics are all below -65dBc at 10MHz, +16dBm output, compared to
   -45dBc at +13dBm for your design (per your table). Further, the
   distortion products of the IC design are essentially all odd-order
   harmonics, while your design shows predominant even-order harmonics.

   Odd-order harmonics are symmetrical, so they do not generate additional
   amplitude-to-phase modulation when the output feeds a squarer/zero-cross
   detector. Even-order harmonics, conversely, *DO* generate additional
   amplitude-to-phase modulation when the output feeds a squarer/zero-cross
   detector. This is very important because the vast majority of
   measurement equipment likely to be fed by a DA/iso amp feeds its inputs
   directly to a ZCD. See reference in next paragraph.

   We have, in the past, disagreed about the importance of low distortion
   in DA/iso amplifiers, but I have satisfied myself that a timing DA/iso
   amp should have, at a bare minimum, -65dBc harmonic suppression. For
   just one reason, see the NIST publication, "The Effect of Harmonic
   Distortion on Phase errors in Frequency Distribution and Synthesis"
   (Walls and Ascarrunz), available at:

   <http://www.ko4bb.com/manuals/73.134.121.2/Harmonic_distortion_and_phase_errors_in_frequency_distribution_and_synthesis_NIST_1995.pdf>

   Best regards,

   Charles



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