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Oscillator Proposal

ok, ok, putting noise through the narrowband passband was NOT a good idea for making a 'clean' oscillator source.

So use the fact that there's a lot of 'logic' potential inside a chip, but external connections cost a fortune...what's wrong with a set of two variable, switchable current sources? One source, one sink to GND driving the RLC node? The idea is to start out with very small current ramp up until reach voltage near rail, switch OFF and turn on he other current source, and head back down, near GND [or neg rail] reverse etc. Now increase the current and keep doing until the voltage turns around on its own BEFORE it reaches the voltage switch points. Make up an appropriate rule.

maybe reverse process starrt at high current and come down in current. But with enough stuff inside the chip, and coming up with appropriate rules, you should be able to make a nice clean, stable output based upon looking like a Function Generator output that is a bit independentof the Q of the external tank.

Reply to
RobertMacy
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It looks just as one would expect: literally worst case phase and amplitude noise. I've done it before with an IF strip. Turn up the gain, and thermal noise is amplified and selected. Turn it up further and inevitable feedback tightens the response into narrower bandwidth, while clipping/limiting destroys amplitude noise (but leaves phase noise intact, aside from the regenerative mechanism).

Tim

--
Seven Transistor Labs 
Electrical Engineering Consultation 
Website: http://seventransistorlabs.com
Reply to
Tim Williams

Can we use a two component tank with 3 nodes, VCC, GND, and a center tapped LC or RC or RLC? The center node is the one remaining pin.

Steve

Reply to
sroberts6328

See, If he allows use of BOTH VCC and Ground, Jim can make a negative resistance device and use a LC with a Tunnel Diode, Lambda Diode, or PUT structure on chip.

The Lambda Diode or PUT can be made with a NPN/PNP or FET pair.

Steve

Reply to
sroberts6328

The "leading order" is for zero R, so there's always a voltage to be observ e in a real circuit. The catch is that the resonant current all flows throu gh Jim's single pin, and the current flow has to be bi-directional because of the capacitor in the RLC.

What you often need to do is to make the negative resistance voltage-contro lled, so that you can use it to control the amplitude of the oscillation - hard limiting can do the same job, but introduces higher harmonics.

In my application I found it useful to put a small gain advance into the ne gative resistance current source - propagation delay will always add some p hase retardation. In my application some 4.5 degrees of phase advance gave the minimum sustaining current, and pushing it up to 45 degrees didn't incr ease it much. Reducing below 4.5 degrees of advance pushed up the sustainin g current quite rapidly.

As Baxandall's 1959 paper pointed out Class C oscillators are essentially e xcited by a string of Dirac spikes, so you've got all the harmonics up to t he limit set by the speed of your switch. Baxandall's class-D replaces the string of spikes by a square wave, where the amplitude of the odd harmonic content drops in proportion to the harmonic number.

Wien bridge oscillators don't have a high Q tank, so they do go in for more sophisticated gain control arrangements.

The gain control in my low distortion oscillator looked rather like the gai n control in one of Jim William's lower distortion Wien Bridges.

--
Bill Sloman, Sydney
Reply to
Bill Sloman

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