Re: Slowman is a LIAR, was OT: Why welfare doesn't work!


On Tue, 16 Sep 2008 19:38:58 -0700 (PDT), bill.sloman@xxxxxxxx wrote:

On Sep 16, 1:59 pm, "Michael A. Terrell" <mike.terr...@xxxxxxxxxxxxx>
wrote:
bill.slo...@xxxxxxxx wrote:

On Sep 15, 2:06 pm, "Michael A. Terrell" <mike.terr...@xxxxxxxxxxxxx>
wrote:
bill.slo...@xxxxxxxx wrote:

On Sep 14, 5:21 pm, "Michael A. Terrell" <mike.terr...@xxxxxxxxxxxxx>
wrote:
bill.slo...@xxxxxxxx wrote:

<snip>

   I have been aware of the 4046 and 9046 CMOS chips for years, Bill.
The built-in VCO is worthless, when you are working around 500 MHz.

The built-in VCO in the 4046 won't do 500MHz

   Isn't that exactly what i said in the line above yours?

Not exactly. The term "worthless" is pejorative. What you meant was
that the VCO in the 4046 was never intended to go anywhere close to
500MHz, which made it irrelevant, rather than worthless.

<snip>

of little relevance in your
application where you were presumably locking your 500MHz (or so) to a
high quality 10MHz crysal-based reference oscillator.

   It was divided down to 100kHz and the VCO was divided into four
overlapping bands to reduce phase noise, and liniearity. The total range
was over 120 MHz, centered near 500 MHz.

So you were required to be able to adjust your local oscillator
frequency in steps of 100kHz.

 We used an ECL prescaler, followed by programmable counters.

So why didn't the designers replicate the internal logic of the MC4044
in ECL to get even better performance. Not that it is something a
technician would think of doing, of course.

   The orginal phase detector was ECL, but the MC4044 worked better. it
had less of the reference bleed through, and was easier to filter from
the VCO's tuning voltage.

That sounds a bit odd. The MC4044 uses gold-transistors as saturating
switches -effectively H-series TTL - while ECL transistors are used as
non-saturating switches, which turn on and off appreciably faster. TTL
power rails always carry switching noise, which modulates the turn-on
and turn-off times, while ECL is mostly balanced, which gives cleaner
rails, and the switching times of non-saturating transistors are much
less sensitve to noise on the power supplies.

If the MC4044 did better than an ECL equivalent, someone must have
screwed up big-time in the design of the ECL-based-phase detector.

No. The TTL adds what is always needed in "perfect" logic... overlap
;-)


In my stroboscopic electron beam tester we were locking 800MHz to a
50MHz crystal-based reference, and used a rather neat ECL-compatible
detector chip that Analog Devices were selling at that time (1988).

   They tested what was availiable, and stareted with a now obsolete ECL
chip, then changed to the MC4044 when it worked better in the same
design.

It does sound as if the original design must have been flawed. It
isn't easy to keep switching noise from influencing the VCO in that
kind of system - IIRR we used a local linear regulator with fairly
hefty local filtering on its input (including a few strategically
placed ferrite chips - SMD beads) to keep the VCO power feed clean in
the stroboscopic electron microscope. My original specification
mentioned that we'd need it. The control voltage input at the VCO went
through a similar passive high-frequency filter, on top of the usual
(much lower frequency) filtering and phase-shifting of the output from
the phase sensitive detector required to keep the voltage controlled
loop stable.

BTW: The VCM core in the TTL MC4024 IS an ECL mechanism (just like in
an MC1658), which is then level-shifted to a TTL output stage.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine Sometimes I even put it in the food
.

Relevant Pages

  • Re: Slowman is a LIAR, was OT: Why welfare doesnt work!
    ... The built-in VCO is worthless, when you are working around 500 MHz. ...    Isn't that exactly what i said in the line above yours? ... in ECL to get even better performance. ... power rails always carry switching noise, ...
    (sci.electronics.design)
  • Re: Slowman is a LIAR, was OT: Why welfare doesnt work!
    ... 500MHz, which made it irrelevant, rather than worthless. ... worse, can cause spurious noise. ... "An inhibit signal is provided to allow disabling of the VCO ...    That should be obvious. ...
    (sci.electronics.design)
  • Re: MAX038 replacement
    ... I am looking for a VCO with sine output like the MAX038, ... Best regards, ...    You were dumb enough to fall into the Not Made Here syndrome by Maxim. ...
    (sci.electronics.design)
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