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What are the advantage and disadvantage of CMOS technology?

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cyw1984

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advantage and disadvantage of bjt and mos

Thank
 

flatulent

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Re: What are the advantage and disadvantage of CMOS technolo

At low clock frequencies it draws very little power.
 

Blackuni

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Re: What are the advantage and disadvantage of CMOS technolo

Hi


Pro's

1. Power eff.
2. compact fabrication & advanced process tech.


con's

1. intrinsic gain of single device.


Thanks
 

Yahia Muhammad

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Re: What are the advantage and disadvantage of CMOS technolo

pros

1- well draws very little power at low freq
2- can make Analog mixed signal on the same chip
3- have two degrees of freedom during design
4- can integrate more transistors \ functions on the same chip

cons

1- consumes high power at high freq
2- better to control vertical dimensions ( BJT ) buring fab
3- BJt has higher gm for the same current
 

leo_o2

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Big mismatch is a drawback of MOS.
 

electronXwork

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Re: What are the advantage and disadvantage of CMOS technolo

CMOS has high input impedance which is a very important characteristic in designing a linear ac amplifier. On the other hand CMOS has low frequency response.

CMOS is useful in Integrated Circuit because of its smaller construction. FETs are more temperature stable.
 

122013137

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hi,
Here is my take on bipolar vs MOS for current mirrors:

1- To make a good current mirror, you want POOR transconductance in the devices for low offsets and noise contributions. With poor transconductance, a small change in input current represents a large change in gate or base voltage. It also takes a larger base or gate voltage change to cause an equal current change at the output current.

For a given current, the bipolar transconductance is constant, which means that the use of degeneration resistors is the only way to reduce transconductance. This means large area, and your matching is now dependant not only on the bipolar, but the resistor matching, too!

For a given current, the MOS transconductance can be changed using W/L. Making a small W/L will make a small transconductance. (Using long L will also help with output resistance of the mirror)

Advantage - MOS.

2- A good current mirror has a low input compliance voltage and a wide output compliance voltage.

Bipolar generally has a lower input compliance voltage than MOS.

MOS generally has a lower output compliance voltage than bipolar. However, a good MOS current mirror (with small W/L) may have an even larger compliance voltage than the bipolar. Degeneration resistors for the bipolar will tend to increase both compliance voltages.

Advantage - possibly slight advantage to bipolar.

3- A good current mirror has a high output resistance.

Bipolar output resistance is fixed for a given current. Again, the degeneration resistors will improve this.

With a MOS device, the output resistance can be changed by changing L.

Both bipolars and MOS can be cascoded for improved output resistance. MOS cascodes are generally easier to make, especially when many current mirrors are needed.

Advantage - MOS.

4- A good current mirror has low noise.

Bipolar current noise is sqrt(2QIB), MOS current noise is sqrt(8/3KTGmB). For a given current, the noise from the bipolar is fixed, unless degeneration resistance is added. Again, low tranconductance (Gm) improves MOS performance for noise.

Advantage - MOS.

5- A good current mirror operates well over a wide range of currents.

Bipolar operation is ideal over many decades of current. MOS hits subthreshold operation at low currents and velocity saturation at high currents.

Advantage - bipolar.

As you can see, the MOS tends to win in most comparisons. However, it can be seen that when certain aspects are critical, there are cases where the bipolar will win.
 

huojinsi

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Re: What are the advantage and disadvantage of CMOS technolo

Pls read the book " Analysis and Design of Analog Integrated Circuits" ! In this books, it has a detailed description.
 

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