Oscillator Proposal

Started by Jim Thompson March 14, 2015
On Sat, 14 Mar 2015 10:07:50 -0700, Jim Thompson  
<> wrote:

> Oscillator Proposal... > > Suppose I have a series RLC, one end grounded, the other end driven by > a chip, how might I make that into an oscillator? > > All wild ideas accepted... this is for a custom chip. > > ...Jim Thompson
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.
"RobertMacy" <> wrote in message 
> OpAmp with NOISE into the non-inverting input. Rfdbk very high Z and a > single external connection to the RLC to GND. Does that produce a > 'narrowband'waveform that 'looks' like an oscillator's output? Hmmm. > time to apply .tranoise and see what THAT simulation shows. > > External connections: Vcc, GND, RLC, Output? if interest is only in the > currents in L, then don't need Output.
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:
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.

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.

On Sunday, 15 March 2015 04:36:52 UTC+11, Phil Hobbs  wrote:
> On 3/14/2015 1:07 PM, Jim Thompson wrote: > > Oscillator Proposal... > > > > Suppose I have a series RLC, one end grounded, the other end driven by > > a chip, how might I make that into an oscillator? > > > > All wild ideas accepted... this is for a custom chip. > > > > ...Jim Thompson > > > > Series RLC is harder than parallel, because to leading order there's no > signal on the pin at resonance. (If it were parallel, you could do a > single-ended version of the MC1648, which you may have heard of.) ;)
The "leading order" is for zero R, so there's always a voltage to be observe in a real circuit. The catch is that the resonant current all flows through Jim's single pin, and the current flow has to be bi-directional because of the capacitor in the RLC.
> You need to arrange a negative resistance at the pin, which isn't hard > to do, and use the AC current to drive the next stage.
What you often need to do is to make the negative resistance voltage-controlled, 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 negative resistance current source - propagation delay will always add some phase 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 increase it much. Reducing below 4.5 degrees of advance pushed up the sustaining current quite rapidly. As Baxandall's 1959 paper pointed out Class C oscillators are essentially excited by a string of Dirac spikes, so you've got all the harmonics up to the 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 gain control in one of Jim William's lower distortion Wien Bridges. -- Bill Sloman, Sydney