Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

[SOLVED] How can I distinguish "feedback loop" and "active gain loop" in a Hartley Oscillator

Status
Not open for further replies.
G

genxium

Junior Member level 3
Joined
Sep 24, 2011
Messages
26
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,386
How can I distinguish "feedback loop" and "active gain loop" in a Hartley Oscillator

I'm currently learning to use harmonic balance simulation for an Oscillator, and started with a Hartley Oscillator, but I don't know how to put the OSCPORT into the original circuit >_<

Here is my diagram that works in real devices test(@125 kHz, amplitude stable for half an hour), can anyone teach me where I can insert an OSCPORT to apply the Harmonic Balance simulation? It's said that I should put it to break the feed back loop, but I have no idea where it is...
 

Attachments

  • Hartley@125KHz.JPG
    Hartley@125KHz.JPG
    67.9 KB · Views: 82
  • result.JPG
    result.JPG
    48.1 KB · Views: 76

Re: How can I distinguish "feedback loop" and "active gain loop" in a Hartley Oscilla

I'll conjecture a guess.

Active gain probably refers to transistor base current flow. (The transistor is the active component in this circuit.) Base current finds a path to ground via one of the coils. Don't break the lines carrying this current.

The feedback loop is the network that particularly creates the oscillations.

You don't want to monitor a wire carrying the base current. It's least likely to yield a sine-like waveform. Therefore don't monitor the bottom coil.

Instead a likely spot for monitoring the feedback loop is at the node joining the coil and two capacitors.

Or if it needs to be through a component, then through the capacitor closest to the transistor. The other components may each contain non-sine current flow, yet together combine to yield a sinewave.

Of course you can always experiment with different locations.
 

Re: How can I distinguish "feedback loop" and "active gain loop" in a Hartley Oscilla

BradtheRad said:
I'll conjecture a guess.

Active gain probably refers to transistor base current flow. (The transistor is the active component in this circuit.) Base current finds a path to ground via one of the coils. Don't break the lines carrying this current.

The feedback loop is the network that particularly creates the oscillations.

You don't want to monitor a wire carrying the base current. It's least likely to yield a sine-like waveform. Therefore don't monitor the bottom coil.

Instead a likely spot for monitoring the feedback loop is at the node joining the coil and two capacitors.

Or if it needs to be through a component, then through the capacitor closest to the transistor. The other components may each contain non-sine current flow, yet together combine to yield a sinewave.

Of course you can always experiment with different locations.
Click to expand...

Thank you so much for the quick reply, I've tried every location I can think of and I just got nothing..... Do you have any idea on the principle of OSCport, like where was it first introduced?

Here're some shots about where I've tried, and how I was totally disappointed >_< I'm wondering if I should consider Hartley as a feedback model or a negative resistance one...
 

Attachments

  • broken@c.JPG
    broken@c.JPG
    87.7 KB · Views: 93
  • broken@e.JPG
    broken@e.JPG
    92.6 KB · Views: 78
  • broken@node2(2).JPG
    broken@node2(2).JPG
    89.7 KB · Views: 74
  • broken@node2.JPG
    broken@node2.JPG
    90.9 KB · Views: 74
  • result.JPG
    result.JPG
    54.1 KB · Views: 80

Re: How can I distinguish "feedback loop" and "active gain loop" in a Hartley Oscilla

Hi genxium,

you can treat the circuit either as an negative-resistance oscillator or as a 4-pole feedback oscillator.
If you need to see and identify the feedback loop you can make use of the "virtual ground" principle, which simply consists in a new ground potential allocation.
* Step 1: Remove the dc supply and use only the small signal equivalent circuit (without the base resistor R2 that only provides biasing);
* Step 2: Realize that the collector is at signal ground - and, thus, connected with the grounded LC circuit;
* Step 3: Remove this ground and instead connect the emitter node to signal ground;
* Step 4: Redraw the circuit - and you have a BJT in common emitter configuration with a frequency-dependent feedback loop between collector and base;
* Step 5: Connect negative supply to the emitter node and add the base resistor connected to ground.

Now, you can identify the feedback loop.
 
Last edited:

Re: How can I distinguish "feedback loop" and "active gain loop" in a Hartley Oscilla

LvW said:
Hi genxium,

you can treat the circuit either as an negative-resistance oscillator or as a 4-pole feedback oscillator.
If you need to see and identify the feedback loop you can make use of the "virtual ground" principle, which simply consists in a new ground potential allocation.
* Step 1: Remove the dc supply and use only the small signal equivalent circuit (without the base resistor R2 that only provides biasing);
* Step 2: Realize that the collector is at signal ground - and, thus, connected with the grounded LC circuit;
* Step 3: Remove this ground and instead connect the emitter node to signal ground;
* Step 4: Redraw the circuit - and you have a BJT in common emitter configuration with a frequency-dependent feedback loop between collector and base;
* Step 5: Connect negative supply to the emitter node and add the base resistor connected to ground.

Now, you can identify the feedback loop.
Click to expand...

Do you mean I should re-construct the circuit like this? I'm not quite sure because the HB simulation still did not give me any response...... i just want some response...>_<
 

Attachments

  • Hartley.JPG
    Hartley.JPG
    107.2 KB · Views: 75
  • result2.JPG
    result2.JPG
    61.7 KB · Views: 81

Re: How can I distinguish "feedback loop" and "active gain loop" in a Hartley Oscilla

Does it matter how I set the OSCPORT parameters?
 

Re: How can I distinguish "feedback loop" and "active gain loop" in a Hartley Oscilla

Genxium, I don't OSCPORT procedures.
The only infrmation I can give to you is how to transfer the Hartley oscillator into a 4-pole diagram showing the feedback loop.
Look at the attachement, which shows
(a) the original small signal equivalent circuit diagram (omitting supply and bias resistor) and
(b) the transformation to a common emitter configuration based on the virtual ground principle.

Perhaps it helps.
 

Attachments

  • virtual_ground.pdf
    300.5 KB · Views: 73

Re: How can I distinguish "feedback loop" and "active gain loop" in a Hartley Oscilla

LvW said:
Genxium, I don't OSCPORT procedures.
The only infrmation I can give to you is how to transfer the Hartley oscillator into a 4-pole diagram showing the feedback loop.
Look at the attachement, which shows
(a) the original small signal equivalent circuit diagram (omitting supply and bias resistor) and
(b) the transformation to a common emitter configuration based on the virtual ground principle.

Perhaps it helps.
Click to expand...

Grateful for that~ I'm reading it
 

Re: How can I distinguish "feedback loop" and "active gain loop" in a Hartley Oscilla

genxium said:
Thank you so much for the quick reply, I've tried every location I can think of and I just got nothing..... Do you have any idea on the principle of OSCport, like where was it first introduced?
Click to expand...

I have no experience with the simulator you're running, nor with OSCport.

Here're some shots about where I've tried, and how I was totally disappointed
Click to expand...

There's still a component you left untried. The capacitor nearest the transistor. It carries what is closest to a sine wave. Its current reverses direction. It biases the transistor hi and low. Its action is the sum and substance of the feedback network.

You posted graphs which showed a couple of what look like ideal sine waves. Where are you taking that signal from?
 

Re: How can I distinguish "feedback loop" and "active gain loop" in a Hartley Oscilla

BradtheRad said:
I have no experience with the simulator you're running, nor with OSCport.



There's still a component you left untried. The capacitor nearest the transistor. It carries what is closest to a sine wave. Its current reverses direction. It biases the transistor hi and low. Its action is the sum and substance of the feedback network.

You posted graphs which showed a couple of what look like ideal sine waves. Where are you taking that signal from?
Click to expand...

I have to be very sorry to say that, the experiment is done now, the mistake I made was that: I forgot to turn the "OSC simulation" of Harmonic Balance from "off" to "on"...........

Sorry for wasting your time >_< !
 

Re: How can I distinguish "feedback loop" and "active gain loop" in a Hartley Oscilla

Ya, this sort of 'gotcha' is ever-present in both electronics and programming. In a lot of other things too.

I get the idea most all the electronics simulators out there are too difficult to use and don't depict graphically enough what happens inside wires. So I've been working on my own homebrew simulator for the past fifteen years. It shows current flow within wires. No need for OSC settings, etc. It's not as sophisticated as Spice or Tina or Matlab, but mine will make it easier to conceptualize what goes on inside a Hartley oscillator, and it allows adjusting values while the sim is running.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top