Oscillator design with differential amplifier used BJT or FET

Dear All
Hi
Thank you for your time to reading my question .
I want design a sine wave oscillator with differential amplifier ( with BJT or FET ) , but i don't know how . and i don't know , that what are the advantages of this oscillator instead of the other oscillators .
Is it possible that you guide me ,please ?
Thanks in Advance
Goldsmith

http://www.simplecircuitdiagram.com/2010/05/10/sine-wave-oscillator/
Is that it ?
http://www.next.gr/oscillators/sine-wave/

goldsmith said:

Dear All
Hi
Thank you for your time to reading my question .
I want design a sine wave oscillator with differential amplifier ( with BJT or FET ) , but i don't know how . and i don't know , that what are the advantages of this oscillator instead of the other oscillators .
Is it possible that you guide me ,please ?
Thanks in Advance
Goldsmith

Click to expand...

Hi Goldsmith,

it sís not easy to answer your question because there is - as ypu probably know - a great variety of different oscillator types/circuits.
Depending on some application oriented demands there properties may be regarded as important or as less important and, thus, may be seen as adavantage (or not).
Think of parameters like frequency range, tunability, cleanliness (THD), output amplitudes,...
For my opinion, on of the advantages connected with the use of a BJT- or FET-based differential amplifier is the following:
Because of the tanh-shaped transfer characteristic of such an amplifier no separate amplitude stabilization mechanism is necessary. More than that, the value of the output signal is known because of the known tanh-shape. And tuning is possible over a good range without change of the oscillation condition.

Dear dselec
Hi
Thank you for your reply.
No , as i mentioned , i want design an oscillator , just with transistor (not op amp ) and at differential mode .
However thank you for your try .
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Dear LvW
Hi
Thank you very much for your reply .
And thank you for your good explanation.
I don't know any thing about this , that , how can i use that pair as an oscillator ? and you told about tuned . is there any oscillator that is based on differential amp , without tune circuit available ? ( for example with RC network or , with RL network )?
And how can i design one of them ? are any rules available ?
Is it possible that you guide me , please?
Best Regards
Goldsmith

goldsmith said:

Dear dselec
Hi
Thank you for your reply.
No , as i mentioned , i want design an oscillator , just with transistor (not op amp ) and at differential mode .
However thank you for your try .
*****************************************************
Dear LvW
Hi
Thank you very much for your reply .
And thank you for your good explanation.
I don't know any thing about this , that , how can i use that pair as an oscillator ? and you told about tuned . is there any oscillator that is based on differential amp , without tune circuit available ? ( for example with RC network or , with RL network )?
And how can i design one of them ? are any rules available ?
Is it possible that you guide me , please?
Best Regards
Goldsmith

Click to expand...

I feel it necessary to explain my arguments in detail:
* At first, the circuit(s) I have in mind do NOT work in symmetrical differential mode: That means, on e of the input always is grounded - but this shouldn`t be any problem for you.
* At second - by speaking of "good" tunability I refer to a circuit which uses the diff. amplifier not as an active oscillator element but "only" as sinus-shaper.
That means: Use the classical way to produce a (tunable) triangle and shape it to a sinusoidal form applying the tanh-characteristic of the diff. pair.
Thus, you can modify the frequency (a) without violating the oscillation condition and (b) with one single passive element only.
* At third, as an alternative to the above, you can use the diff. pair as the only active part (amplifier) in a classical oscillating loop (WIEN, phase-shift, etc.). However, in this case you have to face the (minor?) problem that the design must incorprate the finite input impedance of the base node 8in case of a BJT).
* It should be mentioned, however, that in both cases (sinusoidal shaper or active unit) you need an additional output buffer because of the finite output resistance at the collector (drain) node of the diff. amplifier.
LvW

Check this out ,it has every thing
https://www.electronics-tutorials.ws/index.html

dselec said:

Check this out ,it has every thing
https://www.electronics-tutorials.ws/index.html

Click to expand...

As far as I understand Goldsmith, he does not want to COLLECT different oscillator circuits but rather to UNDERSTAND the different concepts and design strategies.
Therefore, one final statement regarding the use of a differential pair for such purposes.
For my opinion, the most characteristic property of a diff. amplifier - as far as its use for oscillating purposes is concerned - is its ability for SOFT limiting (due to its smooth transfer curve) in contrast to HARD signal limiting as provided by classical amplifier blocks (single transistor or opamp).

Dear dselec
Thank you for your link it is rich and full of good things . but as LvW said , i'm looking for oscillator that based on diff amp .
But thank you for it .
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And Dear LvW
Thank you very much for your explanations .
I learned in this forum that how a diode wave shaper can convert triangle wave to sine wave . but i don't know how a differential amplifier can do it ( as you told ) but i think it is alike with diode wave shaper . is it possible that you guide me , please ?
Thank you and Best Regards
Goldsmith

Hi Goldsmith.

please find as an attachement a circuit that shows how a diff. amplifier is used togethre with a phase shifting network.

Goldsmith,

here is a link for the sine shaper description based on the "soft"-non-linearity of the diff. amplifier transfer curve:
http://www.ecircuitcenter.com/Circuits/Function_Generator/Function_Generator_2.htm

Dear LvW
Hi
Thank you for your attention and help .
With this link i find the answer of many of my questions . i think i can use it for my function generator !
Best Regards and Appreciate
Goldsmith