Guest
On Tuesday, September 30, 2014 9:02:15 PM UTC-4, Bill Sloman wrote:
<snip LTSpice>>
Bill, I'm not sure why you're still beating this horse.
The question was regarding the effect of of mistuning the tank. You
thought it didn't matter. So, I posted two simulations showing tank
tuning does matter.
The issue is objectively, unambiguously resolved.
I deliberately mistuned the simulation specifically to illustrate how
tuning and drift affect the zero-crossing placements. Posting a circuit
with ideal tuning would not have illustrated the deleterious effects
of non-ideal tuning.
Cheers,
James Arthur
On 30/09/2014 11:31 PM, dagmargoo...@yahoo.com wrote:
John wants to produce *exact* zero-crossings. A frequency
multiplier has been suggested in the signal chain.
Simulate this better-than-life quasi-ideal frequency multiplier:
(10mA pulsed current source into 1nF + 22uH LC tank.
Pulse width=500nS, period=5.2uS.)
<snip LTSpice>>
Look at the voltage waveform--are the zero-crossings uniform?
If the LC drifted or were mistuned, would the zero-crossings
stay fixed in time, or would they move?
That's the point.
The tank circuit is resonant at 1.073MHz. The period of the excitation
is 5.2usec, or 192.3KHz, a multiple of 5.578. Moving the multiple to 5
or 6 produces a better looking waveform - with a much higher amplitude,
but still with an amplitude spike at the excitation points.
Two pole tuning clearly isn't good enough, and broad band excitation is
clearly putting a whole lot of energy into the tank circuit at at all
the other harmonics of the excitation frequency.
That James Arthur doesn't understand how to get a high quality waveform
out of a frequency multiplication system isn't all that interesting.
People with rather more expertise in the area do seem to be able to
manage it.
Bill, I'm not sure why you're still beating this horse.
The question was regarding the effect of of mistuning the tank. You
thought it didn't matter. So, I posted two simulations showing tank
tuning does matter.
The issue is objectively, unambiguously resolved.
I deliberately mistuned the simulation specifically to illustrate how
tuning and drift affect the zero-crossing placements. Posting a circuit
with ideal tuning would not have illustrated the deleterious effects
of non-ideal tuning.
Cheers,
James Arthur