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what is the advantages of the bipolar in RF front end?

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liletian

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Hi Guys
In those days, it seems that the power amplifier area is still controlled by bipolar device. I am wondering what is the advantages of the bipolar device compared with CMOS devices in RF front end?
for PA, bipolar device will be have mobility and maybe high breakdown voltage(is it true) and thus can handle high power compared with CMOS devices.
Can anyone comment on this?

For LNA, is there performance advantages of bipolar compared with CMOS device in frequency range lower than 10GHz?
It seems that as the CMOS continueing scaling down, the frequency and NF of the CMOS devices get better and better. Is bipolar still competitive in LNA applications even in high performance application?
Thanks
 

Actually for RF medium to high power output in transmitters FET's are very widespread in their use

For receiver front ends GaAsFET 's and similar are still the preferred choice, primarily because of their low noise figures

Dave
 

davenn said:
Actually for RF medium to high power output in transmitters FET's are very widespread in their use

For receiver front ends GaAsFET 's and similar are still the preferred choice, primarily because of their low noise figures

Dave
Click to expand...
can you explain why bipolar device has low NF?
thanks
 

liletian said:
can you explain why bipolar device has low NF?
thanks
Click to expand...

The FET, be it a GaAsFET etc generally has a much lower noise figure than a bipolar transistor, I suspect you didnt pick up on that

Personally I dont know enough about the internal makeup of the devices to know/understand what controls the NF.
Its not my field of expertise. I just use them, dont manufacture them :)
there may be others here that can give you those more deeper revelations

Dave
 

The BJT/HBT has no 1/f noise, while MOSFET suffers.
because the carrier in mosfet is lateral near the surface, so crystall surface defect will deteriorate noise, while the BJT/HBT is vertical device.
 

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