07-08-2014, 01:02 PM
Low-Voltage CMOS Current Feedback
Operational Amplifier and Its Application
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Introduction
In recent years, great interest has been devoted to the analysis
and design of current feedback op-amp and current-conveyor
integrated circuits [1]-[14], mainly because these circuits
exhibit better performance, particularly higher speed and better
bandwidth, than classic voltage-mode operational amplifiers
(VOA). The current feedback operational amplifier (CFOA)
close-loop bandwidth is independent of its close-loop gain
(provided that the feedback resistance is kept constant and
much higher than the CFOA inverting input resistance) [7]
unlike VOA-based circuits, which are limited by a constant
gain-bandwidth product. The CFOA, shown in symbolic form
in Fig. 1(a), is a four-port network which has a describing
matrix of the following form:
Proposed CMOS Current Feedback Op-Amp
As stated in the introduction, the CFOA could be realized by
the CCII which is cascaded with a voltage follower [2], as
shown in Fig. 1(b). The CMOS realization of the proposed
CFOA, which offers both low-voltage and high drive
capability will be described.
The CMOS realization of the proposed CFOA shown in Fig.
2 consists of two matched parallel connected n-differential
pairs, (M1, M2) and (M3, M4); two matched biasing current
source transistors, (M5, M6); a cascoded current mirror formed
of matched transistors, (M7, M8, M9); and two pairs of matched
source follower transistors, (M10, M11) and (M12, M13).
Transistors M5 and M6 carry equal bias currents (IB), while
transistors (M10, M11) and (M12, M13) produce a positive
voltage shift for the input voltage applied on transistors M11
and M13. All transistors are operating in the saturation region;
the control voltage VC applied to transistor gates M10 and M12
controls the shifting value as
(
Conclusion
A new CMOS CFOA was presented, analyzed, and simulated.
This CFOA has been demonstrated to improve the input stage