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

On Sep 17, 12:56 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@My-
Web-Site.com> wrote:
On Tue, 16 Sep 2008 19:38:58 -0700 (PDT), bill.slo...@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...@xxxxxxxxxxxxxx>
wrote:
bill.slo...@xxxxxxxx wrote:

   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
;-)

So why didn't that get carried over into 4046?

Was it a feature of the design that you failed to document? Or did the
guys that did the carry-over suffer from not-invented-here (which has
certainly happened with stuff I've left behind)?

It was many years before Philips re-invented that particular wheel in
the 74HCT9046 so it would have been a very neat trick to have designed
that overlap the MC4044.

And as far as I'm concerned, anybody using a logic-based phase-
frequency detector to drive a low jitter LO has screwed up big-time.
The logic detector looks at the instantaneous noise on the signals
being compared as they go through zero-crossing, while a product
detector averages the noise on both signals for quite a way around the
the zero-crossing points, so the former opens a much higher bandwidth
window to let in any noise on the signal, while the latter can be -
and always is - heavily low-pass filtered.

A hybrid scheme - using the phase frequency detector to get the LO
into the locking range before going over to a product detector to hold
lock - would seem to offer the best of both worlds.

<snip>

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.

I once cleaned out some nasty - barely sub-nanosecond - jitter from a
TTL-based pulse generator by resynchronising the TTL edges to a 200MHz
ECL clock before translating back to TTL with a 100125.

I do like ECL ...

--
Bill Sloman, Nijmegen
.

Relevant Pages

  • Re: Slowman is a LIAR, was OT: Why welfare doesnt work!
    ... switches -effectively H-series TTL - while ECL transistors are used as ... non-saturating switches, which turn on and off appreciably faster. ... less sensitve to noise on the power supplies. ... frequency detector to drive a low jitter LO has screwed up big-time. ...
    (sci.electronics.design)
  • Re: Is this a gate/drain capacitance problem?
    ... I have a commercial noise source that works this way, but the noise is produces is too low. ... so "spikes" of noise appear on the output as the TTL signal changes state. ... diode will not generate much noise unless it avalacnhes, ... as that of a resistor at room temperature. ...
    (sci.electronics.design)
  • Re: Is this a gate/drain capacitance problem?
    ... a 28V supply and a resistor of about 2 kOhm. ... I have a commercial noise source that works this way, ... TTL signal changes state. ... diode will not generate much noise unless it avalacnhes, ...
    (sci.electronics.design)
  • Re: Is this a gate/drain capacitance problem?
    ... but the noise is produces is too low. ... Applying the TTL without the 28V is not a mode it will be used in. ... I assume the noise figure meter gives the transients before it makes ... zero current in the diode, the diode will generate the same noise power ...
    (sci.electronics.design)