Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
1999-06-29
2001-02-20
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S539000, C323S315000
Reexamination Certificate
active
06191646
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a current source circuit and, more particularly, to a high-precision current source capable of supplying a constant current regardless of temperature change.
Description of the Prior Art
Generally, high-precision current sources have been widely used for high-precision analog-to-digital or digital-to-analog converters. The current sources provide a constant current regardless of temperature change, thus they are used to bias operational amplifiers or to design the reference voltage circuits.
Referring to
FIG. 1
showing a typical current source according to the prior art, a bias current I is supplied using the base-emitter voltage V
BE1
of the bipolar junction transistor Q
1
. That is, the bias current I is obtained as V
BE1
/R.
Here, the resistance R and the base-emitter voltage V
BE1
have positive and negative temperature coefficients, respectively. Therefore, a disadvantage of the current source is that the bias current I(=V
BE1
/R) is a current in strongly negative direction (hereinafter, referred to as IPTAT (inversely proportional to absolute temperature) current).
Referring to
FIG. 2
showing a current source using a thermal voltage V
T
, the current source supplies a bias current I as V
T
ln(NI
E1
/I
B2
)/R, where N is a ratio of the emitter area of the bipolar junction transistor Q
2
to the emitter area of the bipolar junction transistor Q
1
, I
E1
and I
E2
are the emitter currents of the bipolar junction transistors Q
1
and Q
2
, respectively. Here, the positive temperature coefficient in the thermal voltage V
T
is much larger than that in the resistance R. Therefore, a disadvantage of the current source is that the bias current I (=V
T
ln(NI
E1
/I
E2
)/R) is a current in a positive direction (hereinafter, referred to as PTAT (proportional to absolute temperature) current).
Therefore, the currents provided by the above-mentioned current sources may change with changes of temperature.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a temperature-compensated high precision current source that can provide a constant current regardless of temperature change, thereby ensuring the stability of electric circuits. In accordance with an aspect of the present invention, there is provided a temperature-compensated high precision current source, comprising: a) a control means connected to a voltage supply for producing control signal; b) a first current generating means for generating a first current which is proportional to absolute temperature in response to the signals from the control means; c) a first current transferring means for transferring the first current to a common node; d) a second current generating means for generating a second current which is inversely proportional to absolute temperature in response to the signals from the control means; f) a first current transferring means for transferring the second current to a common node; g) the common node for adding the first and second currents and generating a third current which is compensated for a current variation caused by the temperature variation at the first and second current generating means; and h) an output means connected to the common node for receiving the third current from the common node and generating a constant current.
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Cunningham Terry D.
Hyundai Electronics Industries Co,. Ltd.
Jacobson Price Holman & Stern PLLC
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