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Anyone who has the paper or article about the comparison of BJT and CMOS? I'm wondering that which case we should use the BJT device in Bicmos topology.
It is all a matter of economics. MOS takes less room which makes the chips cost less. BJT has higher current capability for a give chip surface area and lower noise in general. That is why BJT is used in the output stage of bicmos amplifiers.
Here are some comparison of BJT/CMOS and BiCMOS as well.
CMOS Vs BJT
=========
-Less power dissipation
-less noise margin
-better packing density
-ability to intergrate large and complex circuits and functions with high yield
-Good switch (in digital design)
BJT Vs CMOS
=========
-high switching speed
-high current drive per unit area
-analog capabilty on amplification
-better noise performance
-high speed intergration
-high transconductance thus will have higher gain.
BiCMOS Circuit Advantages
===================
-Improved speed over CMOS
-Lower power dissipation over BJT
-high performance analog
-Intergration flexibility
-latchup immunity
-high input impedance (CMOS)
-high gain (BJT)
-low noise (flicker noise)
-low input offset voltage for diff pair
-zero offset analog switches
-gain bandwidth product extended
-good voltage reference design
BJT has linearised about an explonential Ic Vs Vbe charecteristics where as MOS is linearised about an near square law Id Vs Vgs charecteristics.
Digital stuff : is mainly concerned with 0 and 1 so CMOS
Analog stuff : gm & ro are imp ... so BJT
Cmos is most ideal for digital ciruits as cmos makes good gates where as Bipolar is used for analog/RF stuff. But now a days most research is aimed at getting analog/RF stuff to work with CMOS as its cheaper and as devices sizes shrink improvement in Ft is seen.
I hope this paper makes some people realize that CMOS can go extremely fast.
"CMOS and SiGe Bipolar Circuits for High-Speed Applications"
by Werner Simburger, et. al., GAAS IC Symposium 2003.
Abstract—Recently, CMOS has been demonstrated to be a
viable technology for very-high-bit-rate broadband and wireless
communication systems up to 40Gb/s and 50 GHz. Advances in
device scaling and doping-profile optimization have also resulted
in SiGe bipolar transistors with impressive performance, including
cut-off frequencies of more than 200 GHz. This paper presents
advances in circuit design which fully exploit the high-speed
potential of a 0.13 µm CMOS technology up to 50GHz and of a
high-performance SiGe bipolar technology up to 110GHz operating
frequency. The combination of advanced circuit techniques
and a state-of-the-art fabrication-process technology results in
continuing the upward shift of the frequency limits.
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