[hpsdr] An high dynamic QSD front-end

[Ahti Aintila]

Bob,

Thank you for your kind words. You are telling about my simple
circuits, but what else can I do? Simple men make simple decisions.

Perhaps we make it still simpler. Some time ago we simulated a
transformerless 180 degree active integrator. Marco received it and if
I am not mistaken of his last private message half an hour ago, he is
already preparing "Gerbers" for that. Do you want my schematic diagram
of that? I may send it later today. The local time is 1 AM. It's time
to go to the bed.

Good night,
Ahti OH2RZ


On 15/01/07, Robert McGwier <rwmcgwier at gmail.com> wrote:
> Congratulations.  Very nice analysis,  very straightforward,  not
> requiring the machinery of Laplace transforms to understand the reasons
> which the "intuition impoverished mathematician" had to do to gain
> intuition.   If you study Leif Åsbrink's WSE hardware you will see the
> great lengths he went to do his "transient fix".   He was working very
> hard to supply the current from a suboptimal current source to overcome
> the transients problems with the four phase  capacitor
> pseudo-integrator.  He had a heuristic understanding of the need some
> time ago but did not go fully virtual ground, current mode with the
> necessary integrator to solve this in the utterly simple ISD Ahti has
> shown us.
>
> Thank you both for a serious elevation of this discussion.  It really is
> time to build hardware.  WARNING:  We definitely want to steer away from
> the FST switches.  FROM MEASUREMENT,  coupled with DDS issues,  they are
> the source of the increasing noise figure.  Marco's plots, as well as
> Phil C's and my measurements of various QSD's using them show this
> inescapable fact.  I think various pieces of analysis have incorrectly
> attributed the measurements but the switches are a major contributor.
> They solved an early problem and we can thank Gerald for finding this
> part and his very gracious publication in QEX and with the SDR-1000.
> But it is time to leave them behind FOREVER.
>
> 73's
> Bob
> N4HY
>
>
>
>
> Ahti Aintila wrote:
> > ***** High Performance Software Defined Radio Discussion List *****
> >
> > Hi Marco and all,
> >
> > After some studies and simulations I have a pleasure to congratulate
> > Marco for the excellent QSD mixer configuration. However, as Marco
> > refers to my ISD experiments with OPA1632 and also mentions 90 degree
> > sampling time better than the 180 degree sampling, I want to add some
> > comment.
> >
> > Marco is completely right (as well as Dan Tayloe) in the case of
> > "passive" integration, that is used in the original "Tayloe detector"
> > and many other configurations after that.
> >
> > In the case of my "active" integrator version (ISD), where the
> > integrating capacitor is in the feedback loop of an operational
> > amplifier, the opposite is true. That is because the current to be
> > integrated flows against to the virtual ground potential (and and also
> > the current flow time is longer), hence the current is not influenced
> > by the accumulated voltage level of the capacitor. In the Tayloe mixer
> > the current is related to the difference between the signal voltage
> > and the accumulated capacitor voltage.
> >
> > I made a couple of simple simulations using my ancient Pspice  Student
> > version. Please, note that the simulation results may be compared only
> > passive against passive and active against active like lemons to
> > lemons and oranges to oranges. I did the simulation using only one
> > channel (I or Q, but not both at the same time) The clock frequency
> > used was 10 MHz and the signal 10.01 MHz. Two amplifiers were used for
> > ISD to get the differential outputs, that is the reason for two
> > sine-wave signals. The QSD was run without amplifiers, so only one
> > output trace. See the pictures:
> > <http://kotisivu.dnainternet.net/ahti/sdr-1000/QSD_ISD_180_90.zip> .
> >
> > By the way, my earlier real measurements in last August gave same kind
> > of results, but I did not record them because the 180 degree active
> > circuit looked as an obvious choice for me.
> >
> > 73 and Prosperous Integration for the New Year,
> > Ahti OH2RZ
> >
> >
>
>
> --
> AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
> TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair
> "If you board the wrong train, it is no use running along the
> corridor in the other direction. " - Dietrich Bonhoeffer
>
>

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