[SI-LIST] Re: S-parameter passivity... Interpreting the results.
- From: "Ray Anderson" <ray.anderson@xxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 20 Jul 2006 16:00:38 -0700
This has been an interesting thread to follow.
John, let me know if I have these items correct:
1) Bias resistors (R6+R7) and (R5+R8) are in parallel and =3D ~ 20k ohms
2) You maintain that the 20K is in parallel with several ohms of ESR in=20
the SAW resonator and will only degrade the resonator Q by a very=20
small amount.
3) You claim that a negative resistance reflected from each transistors
base
effectively increases the Q of the resonator. So you have some
increase
in Q by means of your 'negative resistance' argument which is only
diminished slightly by the parallel bias resistor issue.
4) You mention in one of your e-mails that "the higher the Q, the harder
it=20
will be to control the circuit in production.", but in another
message
you say: "The manufacturing guys liked the circuit because it had =20
a higher yield" (referring to increased resonator Q). Can you
comment?
I read through your patent and didn't notice the Q enhancement as one of
your claims. Did I miss it or was it not claimed due to prior art or
other considerations?
Regards,
-Ray Anderson
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Mike Monett
Sent: Thursday, July 20, 2006 3:24 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: S-parameter passivity... Interpreting the
results.
>Mike,
> Keyless Entry systems are very popular today and most of them have
> a Colpitts Oscillator in them. You probably have a Colpitts
> Oscillator with the bias network you have issues with in your
> pocket right now.
> These Colpitts Oscillators work from -40 degrees C to +85. The
> automotive industry makes a few million of these transmitters a
> year and the warranty return rates are very low.
> At RF frequencies the bias resistors you are identifying are in
> parallel with the resonator not series and yes they do limit the
> Q. To be specific R6 in series with R7 along with R5 in series
> with R8 are in parallel with the resonator. They are there to bias
> the transistor into the active region. The circuit ends up with
> 20,000 ohms or more in parallel with the ohms of resistance of the
> resonator at resonance. It is not a big deal.
> If you would like to address your issues with Colpitts Oscillators
> with the current designers, I can forward an e-mail to them out
> side of this list. However, please be specific. Your statements
> will not hold much weight with people that have spent years
> working full time with the Colpitts oscillator unless you are
> specific.
> I am currently doing a vision system and am back to being a
> Digital Designer except for the EMC and SI work. So if you don't
> mind, I would like to get back to Signal Integrity issues.
>Best regards,
>John
John,
Earlier, you claimed your patent 5,486,793 doubles the Q of the
crystal. I asked for clarification, but your answer failed to
support your claim.
As I stated before, the Thevenin equivalent of both bias networks
are in series with the crystal. This will significantly reduce the
Q. You acknowledge this, but you now claim it is not a big deal.
Thanks for your new information.
Regards,
Mike Monett
Antiviral, Antibacterial Silver Solution:
http://silversol.freewebpage.org/index.htm
SPICE Analysis of Crystal Oscillators:
http://silversol.freewebpage.org/spice/xtal/clapp.htm
Noise-Rejecting Wideband Sampler:
http://www3.sympatico.ca/add.automation/sampler/intro.htm
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