Reference voltage circuit

Details Reference voltage circuit Reference voltage circuit

1981-05-18

1982-11-16

Beha, Jr., William H.

Electricity: power supply or regulation systems

Self-regulating

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

323315, G05F 320

Patent

active

043596800

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention pertains to circuits for generating a reference voltage and more particularly to such circuits which generate a reference voltage independent of variations such as supply voltage, processing and temperature.


BACKGROUND OF THE INVENTION

Tone dialing circuits have come into widespread use in telephone communications. In tone dialing systems each number is represented by a selected pair of tones. Tone generating circuits must be provided for generating these tones. The first and still widely used approach for this tone generation is by the use of discrete LC circuits. However, such discrete circuits are expensive, consume significant power and occupy a relatively large volume of space. However, such discrete circuits have the advantage of being able to properly function over the wide variations in supply voltage provided to the telephone units from the central station.
Tone dialer integrated circuits have been developed for generating the dial tones for telephone applications. These circuits however, have not been completely successful in meeting all of the requirements for telephone system applications. In particular it is difficult to maintain the absolute value of the amplitude of the tone signal within the narrow ranges permitted under telephone specifications. The amplitude of the tone signal must be sufficient to be detected at the central station but cannot be too great such that it saturates the receiving equipment at the central station. Therefore, a stable reference voltage must be produced for regulating the amplitude of the tone signal. For integrated circuits there are numerous factors which can cause voltage levels in a circuit to change. These include variations in supply voltage, which is a serious problem in telephone applications, processing variations in the manufacturing of the integrated circuits and variations in the operating temperature for the circuit.
In view of the above problems there exists the need for a reference voltage circuit which can produce a reference voltage that is essentially independent of variations in supply voltage, processing and temperature.


SUMMARY OF THE INVENTION

The present invention comprises a circuit for producing a reference voltage. A selected embodiment of this circuit is described as follows. First and second power terminals provide a supply voltage to the circuit. Circuit means are connected to the first and second power terminals for maintaining a first node at a first voltage which is essentially independent on the amplitude of the supply voltage provided that the supply voltage is greater than a preset voltage threshold. A first bipolar transistor has a first of the emitter and collector terminals thereof connected to the first power terminal. A second bipolar transistor has a first of the emitter and collector terminals thereof connected to the first power terminal and the base terminal thereof connected to a second node. Circuit means are connected to the first node, the second power terminal and a second of the emitter and collector terminals of the first bipolar transistor for establishing an essentially constant emitter current through the first bipolar transistor. Additional circuit means are connected to the first node, the second power terminal and a second of the emitter and collector terminals of the second bipolar transistor for establishing an essentially constant emitter current through the second bipolar transistor. A first resistor is connected between the base and emitter terminals of the first bipolar transistor. A second resistor is connected between the base and emitter terminals of the second bipolar transistor. A third resistor is connected between the second node and the second power terminal. Further circuit means are connected to the base terminal of the first bipolar transistor and to the first power terminal for generating a control current which is supplied to the second node. Output terminals are connected to the second resistor for providing the desired reference voltage.


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REFERENCES:
patent: 3970875 (1976-07-01), Leehan
patent: 4051392 (1977-09-01), Rosenthal et al.
patent: 4088941 (1978-05-01), Wheatley
patent: 4274061 (1981-06-01), Kraemer

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