Current mirror circuits

Details Current mirror circuits Current mirror circuits

2002-03-26

2003-10-07

Patel, Rajnikant B. (Department: 2838)

Electricity: power supply or regulation systems

Self-regulating

Using a three or more terminal semiconductive device as the...

C327S538000

Reexamination Certificate

active

06630818

ABSTRACT:

FIELD
Embodiments of the present invention relate generally to integrated circuits, and in particular to integrated circuits that include current mirrors.
BACKGROUND
Current mirrors are popular structures that exist in many electrical circuits. Some circuits use a current mirror to reproduce, or “mirror,” an input current to obtain an output current. In most cases, the output and input currents have the same value. In some cases, the output current is proportional to the input current.
FIG. 1
shows a conventional current mirror
100
. Current mirror
100
has a transistor
112
connected to an input node
116
to receive an input current Iin. Transistor
112
connects to another transistor
114
at a reference node
118
. Transistor
114
provides an output current Iout. The input node has an input voltage Vin. The reference node has a reference voltage Vref. Transistor
112
has its drain and gate connected together at both the input and reference nodes. Since the input and reference nodes connect together, Vin equals, Vref. Transistors
112
and
114
typically have the same construction such that they are matched. Hence, Iout flowing through transistor
112
equals Iin flowing through transistor
114
.
In a typical circuit that includes current mirror
100
, the value of Vin is insignificant in comparison to the supply voltage of the circuit. However, as the trend in reducing supply voltage of circuits becomes a necessity for some applications, the value of Vin becomes a significant issue. In some circuits with reduced supply voltage, Vin needs to be reduced to maintain a proper headroom voltage so that the circuits operate properly. However, because nodes
116
and
118
connect together, reducing Vin at node
116
also reduces Vref at node
118
. In some applications, Vref needs to remain at certain value to drive transistor
414
. Therefore, in some applications, as the supply voltage is reduced, current mirror
100
will operate improperly. For
For these and other reasons stated below, and which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need for improved current mirrors.


REFERENCES:
patent: 4792748 (1988-12-01), Thomas et al.
patent: 5079518 (1992-01-01), Wakayama
Rajput, S.S., et al., “A High Performance Current Mirror for Low Voltage Designs”,IEEE Catalog No. 00EX394, (2000), pp. 170-173, No date.

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