Commercially available CFA IC in CMOS technology ????

[engrvip]

Does anybody knows about any commercially avaliable CFA (current feedback amplifier ) IC in CMOS technology ?

The one's I know about are all in BJT or BiCMOS technologies like AD8001 , AD811 , LT1210 etc.

Thanks
Vipul

 

[crutschow]

CMOS doesn't lend itself well to the CFA configuration since a MOSFET is a voltage operated device. A bipolar transistor acts as a low input-impedance current-operated device (please no flak from the pedantics about BJTs actually be voltage operated devices) so it is readily configured to provide the low-impedance current sensitive input of a CFA. Also bipolar transistors are well suited to the high frequency design typical of CFA's.

Why do you want a CMOS CFA?

 

[engrvip]

Well I need to design a CFA but do not have BJT or BiCMOS technology available with me to design a BJT based CFA. Hence was exploring the option to design it in available 180nm CMOS technology.

I went through a paper from Chris Toumazou on a CMOS CFA and was interested in designing one. So what do u suggest is it worth designing one in CMOS technology and what will be the UGB and slew rate specs I can expect from such a cfa ?

 

[FvM]

A bipolar transistor acts as a low input-impedance current-operated device (please no flak from the pedantics about BJTs actually be voltage operated devices) so it is readily configured to provide the low-impedance current sensitive input of a CFA.

Also related to OP input stages, BJTs show as voltage operated devices.

The low impedance inverting input of CFA is designed as common base respectively common gate stage with an input impedance of 1/gm. The gradual difference between BJT and FET in this case is the higher gm of BJT which makes it in fact better suited for high speed CFA designs. But you can design CMOS CFA OPs using similar structures.