a working hardware model of an oscillator using bjt

can i get a circuit of a bjt L-C oscillator which can actually be implemented on hardware? I tried many circuits from internet of hhartley oscillator but none of them was working.

ymmen said:

can i get a circuit of a bjt L-C oscillator which can actually be implemented on hardware? I tried many circuits from internet of hhartley oscillator but none of them was working.

Click to expand...

There are many of them with parts values in Google Images.

If you want LC and only LC...

Then there a only few I've managed to find.

See if this one suits. It is built around a long-tail pair of PNP bjt's.

ymmen said:

can i get a circuit of a bjt L-C oscillator which can actually be implemented on hardware? I tried many circuits from internet of hhartley oscillator but none of them was working.

Click to expand...

Do you know the working principle of the Hartley oscillator or some other (similar) LC oscillators?
Or did you just copy a design that was found elesewhere?
More than that, do you have any idea about the endavoured oscillation frequency?

BradtheRad said:

If you want LC and only LC...

Then there a only few I've managed to find.

See if this one suits. It is built around a long-tail pair of PNP bjt's.

Click to expand...

how can this circuit work, no feedback has been provided. the oscillations will damp after few time.

i unerstood the working of oscillator. but i face difficulty in on what basis the biasing of transistor is done in order to sustain the oscillations?

ymmen said:

can i get a circuit of a bjt L-C oscillator which can actually be implemented on hardware? I tried many circuits from internet of hhartley oscillator but none of them was working.

Click to expand...

How did you check working of it? Did you try to apply kickstart voltage/current or setup initial condition?

UPD. I've read again your post, when you say "implemented in hardware", does it mean in IC or you mean implementation based on discrete components?

Let me share my favourite very reliable LC Pi filter Oscillator using any CMOS Inverter or NAND Gate unbuffered. I've shown the internal structure and equivalent circuit.

The 2nd stage is used as a linear unity gain Amp that can drive 200 Ohms with low distortion but when load drops in Resistance it reaches 50% when it matches the 2x ESR of the CMOS output. Both stages use negative feedback for self biasing and the internal ESD protection with Schottky diodes clamps the high Q gain in the feedback loop, where the C-L-C network gives the stable 180 deg . phase shift at resonance.



The output power into 50 Ohms is around 10dBm at 83 MHz. Scale L & C values only to adjust f. Notice this circuit is identical to a crystal oscillator except the internal LC values of the crystal internally give a Q that is 100x bigger. (>10k)

Press switch to connect load (Simulation link in 1st line) and allow time for coupling cap to charge up.

ymmen said:

how can this circuit work, no feedback has been provided. the oscillations will damp after few time.

Click to expand...

Right, if we try to make the LC oscillate with just one transistor then what you describe will happen. More components need to be added.

The long-tail pair is configured for trigger action. One transistor turns the other off.

The left-right switching action can be made very sensitive. Notice there are no resistors on the bias wires. The transistors are at maximum gain. Overall current flow is kept to a reasonable amount by the emitter resistor.

To show the versatility of the simple Logic Inverter Oscillator.

Shown is 50Hz and 160MHz.

The frequency is independent of supply voltage.

Low distortion with higher Rs impedance ~ 1kΩ. Higher power with Rs=50 suitable for 3.3 ALCV2 logic.

Power in clamp diodes must not exceed rating.