Current controlled CMOS transconductive amplifier arrangement

Details Current controlled CMOS transconductive amplifier arrangement Current controlled CMOS transconductive amplifier arrangement

2001-12-27

2002-11-19

Tokar, Michael (Department: 2819)

Amplifiers

With semiconductor amplifying device

Including differential amplifier

C330S257000, C330S259000, C330S261000, C327S103000

Reexamination Certificate

active

06483383

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to a transconductive amplifier, and more particularly to, a current controlled transconductive amplifier.
BACKGROUND OF THE INVENTION
As shown in
FIG. 1
, with an input voltage Vi a traditional transconductive amplifier has an output current Io in a relation
Io=gm×Vi,
  [
Eq-
1]
where gm is the transconductance of the transconductive amplifier T
1
.
In a general application, such as a GM-C filter, the transconductance thereof is controlled by an input voltage and is not necessary to have a linear relation with the input voltage. While in some applications, such as a telephone, the transconductance thereof is controlled by the line current and requires a linear relation to the line current. As shown in
FIG. 2
, the prior art constructs a transconductive amplifier with a differential stage composed of bipolar transistors. The transconductance of a bipolar transistor is proportional to the current flowing through the bipolar transistor, as a result, linear adjustment of the current flowing through the bipolar transistor can linearly control the transconductance of the bipolar transistor, and thus requirement of linear control of the transconductance of a transconductive amplifier can be met.
However, most present integrated circuits (ICs) are formed by metal-oxide-semiconductor (MOS) processes. In consideration of the consistence of manufacture process and circuit, it is obviously that the circuit shown in
FIG. 2
is unsuitable to such circumstances. Even though the integration of bipolar transistor and MOS process is available, the manufacture processes will become complex and costly. It is thus desired a MOS transconductive amplifier.
Unfortunately, there is a problem presented in the MOS transconductive amplifier for that the transconductance of a MOS transistor and the current flowing through the MOS transistor have the relation
 
gm=dId/dVgs=
2
Kp
(
W/L
)(
Vgs−Vt
)=2(
Kp
(
W/L
)
Id
)
½
.  [
Eq-
2]
That is, the transconductance of a MOS transistor is proportional to the square root of the current flowing through the MOS transistor. Therefore, it cannot obtain a circuit with linear control of the transconductance of a MOS transconductive amplifier by current as that does in FIG.
2
.
SUMMARY OF THE INVENTION One object of the present invention is to provide a current controlled CMOS transconductive amplifier with a linear controllability of its transconductance.
A CMOS transconductive amplifier arrangement, according to the present invention, comprises a control circuit to provide a current to linearly control a first transconductive amplifier having a differential pair composed of a first and a second MOS transistors biased with a bias current, and a second transconductive amplifier matched to the first transconductive amplifier to provide an output coupled to an error amplifier and thus to form a feedback circuit to generate a current to provide the bias current for the second transconductive amplifier whose two inputs are coupled to a resistor therebetween flowing with a current provided by a first current source and output is coupled to a second current source with a current mirrored from the current of the feedback circuit by a current mirror for the bias current of the first transconductive amplifier so as to linearly control the transconductance of the first transconductive amplifier by a current.


REFERENCES:
patent: 4293822 (1981-10-01), McFadyen
patent: 4464632 (1984-08-01), Yoshihisa et al.
patent: 5488330 (1996-01-01), Masuoka et al.
patent: 5621358 (1997-04-01), Pisati et al.
patent: 5757230 (1998-05-01), Mangelsdorf
patent: 5812028 (1998-09-01), Adachi et al.
patent: 5880627 (1999-03-01), Thiel
patent: 5886579 (1999-03-01), Mangelsdorf

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