Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
2000-10-19
2001-10-30
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S542000, C327S512000, C327S513000, C323S313000, C323S315000
Reexamination Certificate
active
06310510
ABSTRACT:
This application claims priority under 35 U.S.C. §§119 and/or 365 to 9924876.7 filed in the United Kingdom on Oct. 20, 1999; the entire content of which is hereby incorporated by reference.
FIELD OF THE INVENTION
This invention relates to an electronic circuit, and in particular to a current reference circuit, which produces a reference current which is independent of temperature and supply voltage.
BACKGROUND OF THE INVENTION
A current reference circuit, implemented using bipolar transistors, is known from U.S. Pat. No. 4,335,346. U.S. Pat. No. 4,335,346 describes a circuit which has two sub-circuits. A first sub-circuit has a negative temperature coefficient, that is the current generated thereby varies inversely with temperature, and a second sub-circuit has a positive temperature coefficient, that is the current generated thereby varies directly with temperature. The first sub-circuit comprises an NPN transistor, the emitter terminal of which is connected through a resistor to ground. As is well known, the base-emitter voltage of a bipolar transistor varies inversely with the temperature. Thus, the current through the transistor, which depends on the voltage across the resistor and the resistance value thereof, will also vary inversely with the temperature. The circuit further includes means for summing the currents generated by the first and second sub-circuits to produce an output current.
SUMMARY OF THE INVENTION
The present invention relates to a circuit which has two sub-circuits. A first sub-circuit has a negative temperature coefficient, and a second sub-circuit has a positive temperature coefficient. The first sub-circuit comprises a first bipolar transistor, the emitter terminal of which is connected through a first resistor to a first voltage supply rail. Thus, the current through the first bipolar transistor varies inversely with the temperature.
The second sub-circuit comprises second, third, fourth and fifth bipolar transistors. The bases of the second and third transistors are connected together, and to the collector terminal of the third transistor. This terminal is further connected to a second voltage supply rail through a second resistor. The emitter of the second transistor is connected to the collector of a fourth transistor, and to the base of a fifth transistor. The emitter of the third transistor is connected to the collector of the fifth transistor, and to the base of the fourth transistor. The emitter of the fourth transistor is connected to the first voltage supply rail through a third resistor, and the emitter of the fifth transistor is also connected to the first voltage supply rail.
The current through the collector terminal of the second sub-circuit is the current generated by the circuit.
The circuit further includes means for summing the currents generated by the first and second sub-circuits to produce an output current.
Importantly, in accordance with the invention, the base of the second transistor, in the second sub-circuit, is connected to the base of the first transistor, in the first sub-circuit. Thus, the second sub-circuit is used to provide the bias voltage for the first transistor, in the first sub-circuit, and it is not necessary to provide any additional bias voltage therefor. This reduces the power required by the circuit, and also reduces the area of the circuit when it forms part of an integrated circuit device.
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Goldman Richard
Wilson Robin
Burns Doane Swecker & Mathis L.L.P.
Callahan Timothy P.
Luu An T.
Telefonaktiebolaget LM Ericsson (publ)
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