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This is part of the physical world. Everything has 1/f noise even though you do not notice the chair legs changing length they do with a 1/f spectrum of length.
You can get even more noise in electronic parts. Look at the data sheets of the parts you plan to use and select the quietest ones.
Generally, metal film resistors are the quietest and JFET transistors are the quietest. Low K value capacitors are also the quietest (mica, air, and glass)
Thank you very much, I still confuse, it seems to me that the flicker noise effect only DC to a certain frequency after that the thermal noise will burry 1/f noise. My question is , in an oscilator, is there flicker noise away from Fc? I mean 1/f from Fc not from DC. if so, what cause it? Is 1/f noise a part of phase noise in the oscilator?
The 1/f noise at very low frequencies of the transistor get put on the sidebands of the sine wave output.
Flicker noise is something different and is caused by imperfections in the parts. In the days of valves/tubes it was thought to be caused by different parts of the cathode emitting more electrons every once in a while.
In the old days carbon resistors were chunks of carbon compressed together and the current path through the grains would vary which would modulate the resistance and cause flicker noise.
Contamination in the processing of transistors was a cause of such noise sources and have been drastically reduced by modern cleanliness practices.
If you are making a synthesizer, the 1/f noise gets drastically reduced by the feedback loop and replaced by the much lower noise of the crystal oscilator reference and the /N counters.
In a communication system, the broad band noise of the amplifier chains gets added to the signal and in many cases is larger than the phase noise sources.
How the 1/f gets on the oscillator output is something that I am not 100% sure of the details. One way to look at it is that the 1/f noise modulates the junction capacitances of the active device. Another way is the amplitude limiting mechanism is a nonlinearity which produces mixing of all signals including the 1/f noise.
Flicker noise and 1/f noise are the terms that are often used in the same context. Actually, the flicker is term used to describe the random noise from almost all linear devices. Characterically for the flicker is the region of lower frequencies in which the noise amplitude declines linear with frequency (1/f region). After corner frequency (fc - usualy given in catalogues) the amplitude distribution can be aproximated as flat (white noise).
Flicker noise is upconverted to oscillating frequency and there is no simple physical description of the process. However, there is a model based on so-called Impulse Sensitivity Function (ISF) of the oscillator that gives fairly good prediction (better than traditional Leeson model). This theory could be found in the book "The design of low noise oscillators" from Hajimiri and Lee, and in many articles from various authors.
I have heard that this model is implemented in the Cadence Spectra RF and believe that if it is so, that and ADS too, for example, uses symilar model.
ISF cannot really resolve flicker noise in an oscillatory system. The reason is that ISF is built around the assumption that perturbation can be desomposed into pure amplitude and pure phase components. It also assumes no memory for the perturbation, i.e. samples of perturbation are not correlated. Both assumptions are not true in the case of flicker noise.
Demir has a nice paper on Modelling of flicker noise in oscillators. He re-defines flicker noise to be able to treat it mathematically and get rid of its zero-frequency singularity. Rael and Abidi have a very nice paper as well.
Hegazi has a nice paper on flicker noise upconversion in varactors.
Flicker noise comes to the output of the oscillator through FM mechanisms not typical upconversion. If you use uponversion-based models you always end up with AM noise not true phase noise. Varactors are one contributor for sure (Hegazi et. al.'2003) and parasitics at the tail current source also enhance it a great deal.
J.J.Rael, A. Abidi,"Physical Processes of Phase Noise in Oscillators," Proc. of CICC 2000.
E. Hegazi and A. Abidi, "Varactor Characteristic, Oscillator Tuning Curves and AM-FM Noise Conversion," IEEE, J. of Solid-State Circuits, vol. 38, no 6, June 2003
Alper Demir, " Phase Noise in Oscillators: DAEs and colored Noise sources," Proc. of ICCAD, 1998
Demir's paper was also re-published in the JSSC early 2003 I believe but can't recall it from the top of my head....
The origins of flicker noise are varied,but it is caused mainly by traps associated with contamination and crystal defects.It is also noted that flicker noise only exists in association with a direct current .
One common technique is to just sample the oscillating device's DC current in a 1MHz BW and then feed that back out of phase into the bias network. This can reduce 1/f effects up to 40dB.
The truth is that flicker noise is one of those phenomena that is only partially understood. In oscillators, for instance, some people report phase noise improvements using DC supply feedback (either active or passive (like an emitter feedback resistor)), but the results are not repeatably reproducible. Also, some report phase noise improvement by using an external circuit to limit the growth of oscillating voltage (like a schottky diode limiter) so that the oscillating device is not saturated (and the trap effect is not provoked as much), but that also is not repeatably reproducible. Bias point does seem to greatly influence 1/F noise conversion onto the oscillating signal, but I do not know if that is acually reducing the 1/F noise, or just reducing the devices ability to upconvert that audio noise.
What is probably going on is that there are five or so low frequency noise sources, and if you add a circuit to fix one of them, there are four more left so you do not really see the noise go away!
The general thinking is to pick the right device, bias it up carefully, and have a lot of supply bypass capacitors, and live with the result.
The theory behind the trapping of charge cariers etc. can be easily researched for your particular device. 1/f noise is a function of your active device size and bias condition so playing with those will reduce it. ADS can simulate it. Just click the calculate noise box in AC simulation. It will calculate the noise voltage at given nodes in the network.
the BJT is the least device have 1/f noise , it s corner frequncy is few KHz , becuase the conduction in BJT is bulk , and there is not interface between materials so the surface states is minimized
that's y the BJT and HBT till now used in Oscillators rather than FETs and HEMTs
As many people mentioned here different transistor families exhibit different levels of Flicker noise. However amplifier topology(CB,CE,CC etc) and design(matching) has a big influence on the up convention mechanics of the noise to the carrier signal. Also although operating in low currents u reduce the device flicker noise that doesn't mean you reduce the PM or AM modulation constant of the amplifier, on the contrary you increase and it with result both your residual phase and amplitude noise to increase. There are always a lot of compromises to make when you want to design a low phase noise (up converted flicker) amplifier. You can simulate those effects in ADS , although manufacturers dont usually provide flicker noise details in their devices models which are essential for simulation.
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