The difference between CMOS high frequency and low frequency? Basically geometry. To make the circuits run faster you primarily have to shrink the dimensions. This will reduce capacitances. (Accompanying provisions may or may not be necessary - depending on the increase in speed desired.)

Regarding the differences between CMOS and other VLSI processes (e.g. bipolar, NMOS): power consumption is a result of the CMOS circuit technology, but process steps depend on the very technology to be realized and differ significantly between technologies.

BTW: you can operate high frequency circuits at low frequencies - but not the other way :)

Dear Researcher

please check this attachments.

regards

http://www.solarbotics.net/bftgu/starting_elect_ic.html

http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=400426&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D400426

As the colleague Dreher said, the main difference between the high frequency and low frequency is transistor size. As the transistor size shrinks especially the channel length, the transit time which is ultimate limiting factor  of the speed of the tranistor, decreases.

It is so that the CMOS technology has gone tremendous evolution since the realization of the MOS transistors and the invention of the mos integrated circuits. High speed is a requirement to speed up the logical and mathematical operations of the digital circuits and systems.

That is high speed and more high speed is a permanent t target of the digital circuits. Not only speed but also the no of transistors that can be fabricated on the chip measured by the integration density. So higher integration density matches the requirement of higher speed. Unfortunately the consumed power density increases consequently. So, scaling down of the transistor size lead to higher speed and higher integration density but increased power consumption density. The main losses in the CMOS circuits is dynamic losses in charging and discharging the parasitic capacitors of the transistors including the gate to source resistance. As the frequency increases the the rate of charging and discharging increase leading to more power consumption. In fact the power consumption is proportional to the frequency.

The integration density is classified into small scale, medium scale, large scale very large scale ultra large scale,... etc., according to the the number of the transistors on the chip.

To scale down the transistor size, there is  a tremendous development in the int grated circuit technology especially photo-lithography,patterning, and doping and depression technology.

The process of down scaling is still going on.

Best wishes

Addon:

what was not so clear until now: the required operating voltage is also going down with shrinking dimensions f the transistors. Unfortunately the maximum voltage tolerated is also decreasing.

One feature to reduce the power consumption is to lower the operating voltage. A good example are Intel PC CPUs where the operating voltage today is adapted dynamically to the CPU clock - which is variable, depending on the performance required. Lower voltage = lower U²*C - hence the dynamic power consumption can be lowered.

On the other hand, the reduction in maximum tolerated voltage is posing significant challenges regarding circuit protection.

Regards

In CMOS VLSI scaling down of the transistor size lead to higher speed and higher integration density but increased power consumption density.How we can reduce power when there is high integration density of transistors?

 Dear Sippee,

As dr. Dreher added, by scaling down the transistor dimensions, the power supply voltage must be decreased to avoid the breakdown of the transistor and also the velocity  saturation of charge carriers in the channel of the transistor. Since the power dissipated in the dynamic processes in the CMOS logic P= F Cgs VDD^2, then by decreasing the power supply voltage VDD will be appreciably reduced. 

There is also power reduction techniques on the algorithmic level by developing system architectures that require less power to implement the same function. There is also techniques to reduce the dissipated power by low power circuit design.

The last thing, one has to cool down the device by heat thinking and  forced coiling methods.

wish you success

Dear Sip,

Pdynamic = CLoadVDD2f.

Lower capacitance = smaller W/L!

Operating frequency is increased by reducing the channel length. But, this increases the power consumption.

Hence a trade-off exists.

Regards,

Suhas. D.

Welcome SUHAS,

it is the power density that counts in the power dissipation formula. So, the capacitance will be that of the cmos transistors per unit area. The capacitance per unit area is equal Cox = epsilon/ tox where tox is the oxide thicness. For scaled down devices the oxide thicness is also scaled which leads to the increase of the Cox. and cosequently the capacitance per unit area. So,scaling down will increase the the power density and increased heating.Thank you for exciting this issue.

Hello all,

regarding oxide thickness: when shrinking a circuit, usually the oxide thickness is also reduced - - - only to find out, that e.g. flash memory cells are no longer capable to hold the value as long as required :) (This has happened several times with different manufacturers.)

Oxide thickness is not necessarily coupled with structure size - you can have thicker oxides on shrinked geometries. But you have to account for that.

Regards

Yes colleague Dreher, for transistor scaling there is a good power point presentation in the Link;http://scale.engin.brown.edu/classes/EN0291S40F06/lecture02.pdf

Tan you for commenting my answer. It is a good addition.

Best wishes.

high speed cmos:

http://www.springer.com/la/book/9780792382201

https://www.ecse.rpi.edu/courses/cstudio/data%20sheets/DL129-D.PDF

http://www.ti.com/litv/pdf/scaa034c

2

http://dlia.ir/Scientific/e_book/Technology/Electrical_Nuclear_Engine_Electronics/TK_8300_8360_Photoelectronic_Devices_(General)_/023643.pdf

low

http://www.eceietbujhansi.org/books/Analog%20Integrated%20Circuits/radio%20frequency%20integrated%20circuits.pdf

Dear All,

Can anyone help me in understanding the relation between the channel lenght of cmos and its operating frequency?

Is it correct to say smaller the device higher the operating frequency?