[time-nuts] SMD TADD-1 distribution amplifier - seekingcomments and suggestions?

timeok at timeok.it timeok at timeok.it
Fri Dec 18 07:49:31 UTC 2015


one of the most important spec is the channel to channel separation. Do you have done some measurements?

Luciano
www.timeok.it



On Thu 17/12/15 20:44 , Anders Wallin <anders.e.e.wallin at gmail.com> wrote:

> First prototype assembled today, tested with 12 VDC SMPS wall-wart supply
> and with 12 V lead-acid battery.
> Compared against a SRS FS710 and a Symmetricom 6502 and John Ackermann's
> 2007 plot:
> http://www.anderswallin.net/2015/12/frequency-distribution-amplifier-first-
> tests/[1]
> 
> What does the 6502 do differently? It is maybe 5 to 8 dBc/Hz better both
> in
> PN and AM from around 1 kHz and out.
> 
> My 'ultra-low-noise DC-supply' in the form of a lead-acid battery improves
> things somewhat, but some spurs still remain:
> http://www.anderswallin.net/wp-content/uploads/2015/12/2015-12-17_fda_spurs
> _and_comments.png[2]
> interpretations and explanations are welcome!
> The board was not enclosed in a metal can for these tests.
> 
> The regulator is an LP38798
> http://www.ti.com/lit/ds/symlink/lp38798.pdf [3]
> 
> Anders
> 
> On Tue, Dec 1, 2015 at 12:54 AM, Bruce Griffiths  wrote:
> 
> > Anders
> > U101 only needs to have a gain of 1 at dc so replace R104 and R105 with
> a
> > capacitor connected to ground.
> > Adjust the other components of the gain determining network
> > accordingly.Also the junction of the power supply divider R102 and R103
> > should be heavily capacitively bypassed to ground and a resistor placed
> > between this junction and U101's noninverting input.
> >
> > Excess Sub Hz PN is usually due power supply noise or thermal
> fluctuations
> > due to air currents/ convection.
> > Most of the so called super regulator circuits should be more than quiet
> > enough with an LM329 reference.A damped LCR filter at the input will
> > improve the PSRR at switchmode output frequencies.
> >
> > Bruce
> >
> >
> >
> > On Tuesday, 1 December 2015 9:02 AM, Anders Wallin 
> anders.e.e.wallin at gmail.com> wrote:
> >
> >
> > HI all,
> > I need to build a few distribution amplifiers (>90% for 10MHz, sometimes
> > maybe 5MHz) and instead of reinventing the wheel I decided to try to
> > modernize the TADD-1 into an all (almost) SMD design. Here are some
> draft
> > sketches:
> >
> >
> http://www.anderswallin.net/2015/11/frequency-distribution-amplifier-plans-
> a-k-a-smd-tadd-1/[4]
> >
> > Does this sound/look reasonable or crazy?
> > Any suggestions for op-amps to try and/or compare to the AD8055?
> > What causes the extra phase-noise below 1 Hz offset in John A's result:
> >
> https://www.febo.com/pages/amplifier_phase_noise/amplifier_phase_noise.png
> [5]
> >
> > Suggestions for a low noise DC-regulator circuit? The 12-24VDC supplied
> to
> > this board will most likely come from a switched-mode PSU, so filtering
> of
> > common-mode noise is mandatory.
> > I found the TI LP38798 shown in the schematic by googling - if someone
> has
> > a proven a measured design that would be a safer choice. In any case
> more
> > filtering (e.g. ferriites) is probably a good idea.
> >
> > This design will be available on my blog or on github when it is done -
> if
> > anyone is interested.
> >
> > Thanks,
> > Anders
> > _______________________________________________
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> >
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> 
> 
> Links:
> ------
> [1]
> http://webmail.timeok.it/parse.php?redirect=http://www.anderswallin.net/201
> 5/12/frequency-distribution-amplifier-first-tests/[2]
> http://webmail.timeok.it/parse.php?redirect=http://www.anderswallin.net/wp-
> content/uploads/2015/12/2015-12-17_fda_spurs_and_comments.png[3]
> http://webmail.timeok.it/parse.php?redirect=http://www.ti.com/lit/ds/symlin
> k/lp38798.pdf[4]
> http://webmail.timeok.it/parse.php?redirect=http://www.anderswallin.net/201
> 5/11/frequency-distribution-amplifier-plans-a-k-a-smd-tadd-1/[5]
> http://webmail.timeok.it/parse.php?redirect=https://www.febo.com/pages/ampl
> ifier_phase_noise/amplifier_phase_noise.png[6]
> http://webmail.timeok.it/parse.php?redirect=https://www.febo.com/cgi-bin/ma
> ilman/listinfo/time-nuts[7]
> http://webmail.timeok.it/parse.php?redirect=https://www.febo.com/cgi-bin/ma
> ilman/listinfo/time-nuts[8]
> http://webmail.timeok.it/parse.php?redirect=https://www.febo.com/cgi-bin/ma
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