Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
1999-11-12
2001-03-06
Wong, Peter S. (Department: 2838)
Electricity: power supply or regulation systems
Self-regulating
Using a three or more terminal semiconductive device as the...
C323S317000
Reexamination Certificate
active
06198267
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a current generator for delivering a reference current having a value which is proportional to the absolute temperature comprising an output terminal for delivering the current; a first and a second supply terminal for receiving a supply voltage; a first bipolar transistor having a collector coupled to the first supply terminal, a base, and an emitter; a second bipolar transistor having a collector coupled to the first supply terminal, a base, and an emitter; a first current source coupled in between the second supply terminal and the emitter of the first bipolar transistor; and a second current source coupled in between the second supply terminal and the emitter of the second bipolar transistor.
Such a current generator is known from the publication: “Micropower CMOS Temperature Sensor with Digital Output”, IEEE Journal of Solid-State Circuits, Vol. 31, no. 7, July 1996, pages 933-937. In the known current generator the first and the second current sources are formed by respectively first and second PMOS-transistors of which theirs sources are coupled to the second supply terminal. A drain of the first PMOS-transistor is coupled to the emitter of the first bipolar transistor. A resistor is coupled in between a drain of the second PMOS-transistor and the emitter of the second bipolar transistor. The bases of the first and the second bipolar transistors are coupled to the first supply terminal. An operational amplifier is coupled with an inverting input to the drain of the first PMOS-transistor, with a non-inverting input to the drain of the second PMOS-transistor, and with an output to gates of the first and second PMOS-transistors. The operational amplifier controls a control voltage at the gates of the first and second PMOS-transistors in such a manner that the voltage difference between the drains of the first and the second PMOS-transistors is virtually equal to zero. By appropriate dimensioning of the components the voltage across the resistor is proportional to the absolute temperature. Also the currents flowing through the first and the second PMOS-transistors are proportional to the absolute temperature. In the known current generator a reference current which is proportional to the absolute temperature can be generated by the addition of a third PMOS-transistor of which its gate and source are connected to respectively the gates and sources of the first and second PMOS-transistors. The reference current can then be taken from the drain of the third PMOS-transistor.
Since reference currents are very often necessary in electronic circuits there is a need for alternative solutions.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a reference current of which the value is proportional to the absolute temperature.
To this end, according to the invention, the current generator of the type defined in the opening paragraph is characterised in that the current generator further comprises a resistor branch of resistors coupled in series, whereby a first end point of the resistor branch is coupled to the base of the first bipolar transistor, a second end point of the resistor branch is coupled to the base of the second bipolar transistor, and an internal node of the resistor branch is coupled to the first supply terminal; and regulation means for regulating the voltage between the emitters of the first and the second transistor to virtually zero volt by adapting a current flowing through at least a part of the resistor branch. This structure opens the possibility of chopping (interchange) the first and second bipolar transistors. The current generator may further be characterised in that the resistor branch comprises a first resistor coupled in between the first end point of the resistor branch and the internal node of the resistor branch; and a second resistor coupled in between the second end point of the resistor branch and the internal node of the resistor branch, and in that the at least part of the resistor branch is formed by the second resistor. The special construction of the novel current generator opens the possibility of designing a current generator which delivers a more accurate reference current. The first and the second resistors are coupled in series with the bases of the first and the second transistors instead of with resistors in series with the emitters of respectively the first and second transistors, as is common practice in the prior art. In this way the undesired resistances of switches which can be put in series with the first and second resistors in order to interchange periodically (chopping) the first and the second transistors for increasing the accuracy of the reference current, have a smaller effect. The effect is smaller because in the novel current generator the base currents of the first and second bipolar transistors flow through respectively the first and the second resistors instead of the emitter currents as is the case in known prior art. As a result the values of the first and second resistors are much higher than in the known prior art. This has the advantageous effect that the aforementioned undesired resistances have a less disadvantageous effect on the accuracy of the reference current. For this purpose the current generator of the type defined in the opening paragraph may alternatively be characterised in that the resistor branch comprises a first resistor coupled in between the first end point of the resistor branch and the internal node of the resistor branch, and a second resistor coupled in between the second end point of the resistor branch and a further internal node of the resistor branch, and a third resistor coupled in between the internal node and the further internal node; and in that the current generator further comprises a third current source, first switching means arranged for alternately coupling either the internal node to the first supply terminal during a first phase or the further internal node to the first supply terminal during a second phase, second switching means for alternately coupling either the second end point of the resistor branch to an output terminal of the regulation means during the first phase or the first end point of the resistor branch to the output terminal of the regulation means during the second phase, and third switching means for alternately coupling either the third current source in parallel with the first current source during the first phase or the third current source in parallel with the second current source during the second phase. By so doing the first and the second bipolar transistors are in fact interchanged periodically (chopped). As a consequence the effect of a matching error between the first and the second bipolar transistors is cancelled, and thus a higher accuracy of the reference current is achieved.
This embodiment may further be characterised in that the regulation means comprise an amplifier having a non-inverting input coupled to the emitter of the first bipolar transistor, an inverting input coupled to the emitter of the second bipolar transistor, a non-inverting output, and an inverting output; a differential to single-ended converter having a non-inverting input, an inverting input, and an output; fourth switching means for alternately coupling either the non-inverting output and the inverting output of the amplifier to respectively the non-inverting input and the inverting input of the differential to single-ended converter during the first phase or the non-inverting output and the inverting output of the amplifier to respectively the inverting input and the non-inverting input of the differential to single-ended converter during the second phase; and an output transistor having a control electrode coupled to the output of the differential to single-ended converter, a first main electrode coupled to the output terminal of the regulation means, and a second main electrode coupled to the output terminal of the current generator. The fourth switching means provide a stable behavio
Bakker Anthonius
Huijsing Johan H.
Laxton Gary L.
U.S. Philips Corporation
Wieghaus Brian J.
Wong Peter S.
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