I understand but this looks good enough.For giggles and kicks I tried to make the tank circuit with an oscillator with <10mΩ source impedance but not consume much power driving the series tank circuit.
It was a bit problematic but it oscillated at resonant frequency. The challenge was to get Barkausen criteria with positive feedback and minimal DC offset into a 50mΩ current shunt with negative feedback for DC operating point and not suck much current. I used +/- 3.7V to DC couple and prevent DC current thru the inductor.
But in the time I spent on it, it wasn't good enough to be reliable for a wide range of LC values.
View attachment 94455
To make a good sample and hold , you can use CMOS analog switches but low bias FET input OP Amps and low leakage caps ( Plastic film)
How about designing it to do what you want? What kind of question is that?...Let's say I have a system which sweeping so fast that it is going through the resonant frequency. If I want to make it more sluggish or let us say I want it to lock some KHz above the resonant frequency (so that it is more practical), how would I go about it?
My question was that is it practical to stop way before it hits resonance to avoid frequency sweeping to the capacitive side, as a precaution. Or would it always lock at resonance.How about designing it to do what you want? What kind of question is that?
You have to go through resonance in order to detect it.Let's say I have a system which sweeping so fast that it is going through the resonant frequency.
Only if you're clairvoyantis it practical to stop way before it hits resonance
Haha. I understand now.You have to go through resonance in order to detect it.
Only if you're clairvoyant.
Thank you. I have decided to go with the latest model.100kHz would be nice and offered in some.
This is what bought.
http://www.extech.com/instruments/product.asp?catid=56&prodid=349
~$210 http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_198678_-1
1mΩ resolution
with 0.1uH & 5 digit resolution. More expensive than than 1uH resolution, less than 0.01uH.
120 HZ and 1kHz std.
I doubt any Chinese Clones< $100 can match performance.
I would suggest for you , the next model up
**broken link removed**
5 frequencies up to 100kHz
Inductance 20μH, 200μH, 2000.0μH, 20.0000mH, 200.00mH ±(0.5%rdg + 5 digits)
2000.0H, 20.000H, 200.00H, 2000.0H (DF<0.1)
Capacitance 20pF, 200pF, 2000pF, 20.000nF, 200.00nF, 2000.0nF ±(0.5%rdg + 5 digits)
20.000μF, 200.00μF, 2.0000mF, 20.00mF (DF<0.1)
Resistance 20.00Ω, 200.00Ω, 2.0000kΩ, 20.000kΩ, ±(0.5%rdg + 5 digits)
200.00kΩ, 2.0000MΩ, 20.000MΩ, 200.0MΩ
DF (with C) 0.000 to 999
Q 0.000 to 999
Phase ±90°
Test Frequency 100Hz/120Hz/1kHz/10kHz/100kHz
but only 0.01Ω resolution.
Wow Tony StewartEureka. I think I have a working micropower clock generator that starts instantly from a parallel tank circuit
Here's is my interactive simulation.
Try this
Negative feedback is for self Bias with small hysteresis reduction.
Positive feedback is to satisfy Barkhausen criteria with Tank circuit.
Try click switch to change frequency 3x ,
Press Reset to see startup operation in slow motion.
Thus with gain >>1e6 in a high speed comparator, the logic level feedback is integrated to a sinewave current due to parallel resonance is much higher than resonant reactance ~< 1 Ohm so the Q should be high and current is limited by 3.7V / 100K iuf using a LipPo battery. Noise abatement is critical, as AM radio will be stronger than the injected signal using shielded or twist pair with large CM choke ( ferrite torroid). Of cource add RF cap across comparator close to chip. Wires cannot be shown like in schematic to DUT with 100 uVpp for example.
View attachment 94479
There is still a challenge to choose the right comparator. They have high speed , low latency but also low gain compared to Op AMPs.Wow Tony Stewart
This works like a million dollars on simulation. I'll try it doing it practically today itself.
Thanks a lot. You're a genius.
If you want a dead simple oscillator that runs off an LC tank, then a negative resistance oscillator using a Lambda diode is about as simple and reliable as you can get. For example:
**broken link removed**
The oscillator circuit is at the bottom of the page.
I've used essentially the same circuit for measuring resonance of LC tanks.
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