[SOLVED] [Help] Can anyone please explain how this circuit works?

[Akeel Qadir]

[Moved] how this circuit works ? can any body explains?

hi guys....



can anybody help me how this circuit works????
i need detailed working of this oscillator ??? please help

 

[BradtheRad]

re: how this circuit works ? can any body explains?

Are you allowed to use a simulator? Did the circuit work in a simulator?

I had to add a few components to my simulation. Without them I got convergence errors.

Theoretically...

The upper LLC loop oscillates around the circle one way, then the other.

One mosfet turns on, then the other. Each time a bit of current is pulled from the power supply, which provides the slight kick needed to maintain oscillations.

 

[Akeel Qadir]

re: how this circuit works ? can any body explains?

yes i am using spectre circuit simulator... no it is not working in simulator.......

and how can mosfet turns on if vdd is less than threshold.....? in this circuit vdd is 80mv.... so i don't think mosfet will turn on .... and more over do you have any idea what is the purpose of lower inductors in this circuit?

 

[FvM]

Re: [Moved] how this circuit works ? can any body explains?

yes i am using spectre circuit simulator... no it is not working in simulator

Sure you are using suitable transistor parameters?

The transistor symbol (assumed it's sketched correctly) shows an depletion mode MOSFET (negative Vth), did you consider this in your simulation? The source inductors may represent parasitic (bond wires) or intentional introduced inductance. They partly change the oscillation condition, the cross-coupled oscillator can work without it as well.

 

[BradtheRad]

Re: how this circuit works ? can any body explains?

yes i am using spectre circuit simulator... no it is not working in simulator.......

This screenshot shows what I had to do, to make it work in Falstad's simulator.

and how can mosfet turns on if vdd is less than threshold.....? in this circuit vdd is 80mv.... so i don't think mosfet will turn on

I found it necessary to increase the power supply to 1.5V. That was barely sufficient to get oscillations going in this simulator.

Sometimes a bit of experimentation is required, in real life and simulations.

 

[BigBoss]

Re: [Moved] how this circuit works ? can any body explains?

It's a simple cross-coupled LC Oscillator with Noise Filtering (by Ls).In order to simulate such circuits, a start-up simulation trick should be used to excite the oscillator.
For instance a step-up current may be injected into the circuit during a limited period or a step-up voltage source can be used to excite the circuit states otherwise spectre will not start-up the oscillator and all node or branch state will keep their positions so the osciallator wil be in a DC steady state.

 

[Akeel Qadir]

Re: how this circuit works ? can any body explains?

you could be right... but i can't increase my power supply as i am trying to simulate it under ultra low power condition .... (Thermal energy harvesting) ..... my vdd must be in between 80mv to 200mv....

- - - Updated - - -

as i am trying to simulate it under ultra low power condition .... my vdd supply could very form 80mv to 200mv..... so what do you think, what kind of step-up voltage source should i use.... can you explain details of step-up voltage source... e.g

1). what should be the time period for this step-up voltage source?
2). rising time? falling time? time period?
3). what should be the peak value of this source?

 

[BigBoss]

Re: how this circuit works ? can any body explains?

you could be right... but i can't increase my power supply as i am trying to simulate it under ultra low power condition .... (Thermal energy harvesting) ..... my vdd must be in between 80mv to 200mv....

- - - Updated - - -

as i am trying to simulate it under ultra low power condition .... my vdd supply could very form 80mv to 200mv..... so what do you think, what kind of step-up voltage source should i use.... can you explain details of step-up voltage source... e.g

1). what should be the time period for this step-up voltage source?
2). rising time? falling time? time period?
3). what should be the peak value of this source?

That's not an issue.You may increase VDD-for instance- 1V at the beginning for-let's say during 200ns-then you drop down to typical value to make the circuit to trig.It won't change your current consumption in "steady state".While simulating this VCO with PSS ( or transient ) add a proper stabilization time.After this stabilization time, avarage current consumption will be as desired.

For instance...

Use a Piecewise Linear VDC such as 0V@0s ,0V@100ns@,1V@105ns,@1V@110ns,200mV@115ns etc..

Try and see..

 

[FvM]

Re: [Moved] how this circuit works ? can any body explains?

Non-equilibrium conditions are usually sufficient to start the oscillator, in this case asymmetrical initial voltage.

But you didn't yet tell if you put a suitable (depletion mode) transistor into the circuit that can work with 100 or 200 mV.