Help with Electronic Oscillators

Ok, Here I come again with question
What is the major drawback of an electronic oscillator (LC or RC oscillators)? What is the solution to that drawback?

Not sure what is the 2nd part of the question is asking. Is it asking how an electronic Oscillator work or something like that?
SO from the question I would have to say either LC or RC oscillator
I know that L-C circuit works as an oscillator circuit at its resonance.

If anyone can help me..thanks for your time.

Hi,

Probably the worst problem with LCR or RC is that the frequency tends to drift and the circuit usually has to be tuned.
Crystal oscillators are more stable and are more accurate from the first time they are turned on without any tuning.
PLL comes in next.

MrAl said:

Hi,

Probably the worst problem with LCR or RC is that the frequency tends to drift and the circuit usually has to be tuned.
Crystal oscillators are more stable and are more accurate from the first time they are turned on without any tuning.
PLL comes in next.

Click to expand...

thanks for the quick reply.
PPL is Phase-locked loop
didnt learned about that yet I think.
So for the solution part this can be say Electronic oscillators are more stable and are more accurate from the first time they are turned on without any tuning.
as you mentioned....thanks for the help.

An LCR or RC or PLL oscillator is an electronic oscillator. Only oscillators made with a PLL that has a master oscillator controlled with a crystal are "more stable and are more accurate from the first time they are turned on without any tuning."

PPL circuit uses negative feedback right?
Crystal in parallel mode acts like ans inductor RLC filter. There are two types of Crystal.
Pierce crystal oscillator and Colpitts crystal oscillator.

Look up Phase Locked Loop in Google. It does not use negative feedback.
A PLL (not PPL) is used with a crystal oscillator and a counter to make a frequency synthesizer that creates one of many accurate frequencies.

audioguru said:

Look up Phase Locked Loop in Google. It does not use negative feedback.
A PLL (not PPL) is used with a crystal oscillator and a counter to make a frequency synthesizer that creates one of many accurate frequencies.

Click to expand...

thanks...we havent cover about PPl part yet...so wont have to worry abt right now...I think...
just to make sure to find the output frequency of crystal oscilloscope for both (Colpitts and Pierce) we use this formula FS=1/(2π√LS C) which is the resonant frequency
and C is C=(CS CP)/(CS+CP )

mkforlife10 said:

thanks...we havent cover about PPl part yet...so wont have to worry abt right now...I think...
just to make sure to find the output frequency of crystal oscilloscope for both (Colpitts and Pierce) we use this formula FS=1/(2π√LS C) which is the resonant frequency
and C is C=(CS CP)/(CS+CP )

Click to expand...

You are mixing up everything in your text:
1) There is no PPL. (It is a PLL)
2) There is no crystal oscilloscope. (It is a crystal oscillator).
3) The frequency of a crystal is marked on it but it might work in a harmonic multiplier circuit.

audioguru said:

You are mixing up everything in your text:
1) There is no PPL. (It is a PLL)
2) There is no crystal oscilloscope. (It is a crystal oscillator).
3) The frequency of a crystal is marked on it but it might work in a harmonic multiplier circuit.

Click to expand...

damn...tooo much studying and stress I guess...thanks for the correction...

It is called, Dyslexia.

Or a Foreign student trying to grasp the English language as well as the electronics. Give the guy a break. Most of us know roughly what he is asking about.

LC/RC/LCR oscillators rely on tuning components that are vulnerable to temperature changes. A Crystal oscillator is less so and often hides a badly designed oscillator circuits in the first place. A well designed crystal oscillator should work close to its intended frequency without the crystal (shorted or open cct) depending on the topology chosen. The crystal will hold it there if the surrounding circuit is well designed.

In order of very rough accuracy,
Atomic. Usually rely on the transition periods in a Caesium atom. Similar to Off Air GPS standards.
TCXO. Temperature compensated crystals with known drifts and a thermometer to add and subtract clock cycles.
Oven Oscillators that keep a crystal at a know stable frequency.Often used as references in measuring equipment like a spectrum analyser.
Crystals, as previously mentioned.
Laser trimmed RC. Often used in microprocessors like the SiLabs 8051 series among others.
Stable LRCs using silvered mica caps and moulded stable inductors.
Out of the box using RLCs in your collection that can drift badly.

mkforlife10 said:

Ok, Here I come again with question
What is the major drawback of an electronic oscillator (LC or RC oscillators)? What is the solution to that drawback?

Not sure what is the 2nd part of the question is asking. Is it asking how an electronic Oscillator work or something like that?

Click to expand...

I suppose, the question aims at the following problem of any electronic oscillator which sounds like a contradiction:

A linear (harmonic) electronic oscillator must contain a certain non-linearity in order to produce a good (low THD) sinusoidal signal

The reason is as follows: The oscillation condition requires (for steady-state self-sustained oscillations) a loop gain of exactly unity.
This can never be achieved by design (parts tolerances, aging, etc.).
Therefore - also to ensure a safe start of oscillations - the loop gain is designed to be somewhat larger than unity.
This leads to oscillations with rising amplitudes - until limiting occurs (power rails) causing signal distortion (amplitude clipping).
Therefore, it is advisable to include a "soft-limiting" non-linear device (thermistor, controlled FET resistor) which reduces the otherwise unacceptable THD to a lower value.
That is the solution to the drawback. OK?

One final remark (to complete the answer): The mentioned "soft-limiting" action with the aim to reduce the loop gain for rising amplitudes can be accomplished also by the non-linear transfer characteristic of a transistor. That is the reason simple transistor oscillators can be found in the literature without any additional amplitude control mechanism.

Frequency error/drift and distortion of sinewave output.
Frequency error/drift can be decreased by using more accurate components (tend to be lower drift), lower drift components, temperature stabalized enviroment, or non-linear components like a crystal.
Distortion is caused by too much gain, but higher gain capability is required to guarantee starting under all component/enviromental variations. Adding a constant gain feature with feedback is one method of lowering distortion, and post filtering is a second method of obtaining sinewave purity.