Electricity: power supply or regulation systems – Self-regulating – Using a three or more terminal semiconductive device as the...
Patent
1997-05-02
1998-06-30
Wong, Peter S.
Electricity: power supply or regulation systems
Self-regulating
Using a three or more terminal semiconductive device as the...
323314, 36518909, G05F 316, G11C 1604
Patent
active
057739676
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a voltage reference of the type called a band gap.
BACKGROUND INFORMATION
Voltage references are commercially available in a wide range as integrated circuits. Their temperature gradients are calibrated during manufacture to specific tolerance parameters to compensate for a physically dictated temperature coefficient. Aging, however, can eliminate the calibration to the extent that the reference will, in certain circumstances, yield a voltage not allowed for by the downstream circuitry. The result can be an increased functional risk to the downstream circuitry.
SUMMARY OF THE INVENTION
The voltage reference in accordance with the present invention features the advantage that it can be repeatedly tested at any time throughout its life. Another advantage is that the repeated testing can be accompanied by repeated self-calibration. The voltage leaving the reference will accordingly be very reliable, and defects and aging phenomena can be detected and eliminated.
The self-testing and/or self-calibration can be carried out with simple switches, preferably MOS switches, which is a particular advantage. These switches are inactive and will not affect the voltage reference during normal operation. At prescribed times, when the operating voltage is applied or during demands advanced by the controls for example, the switches are activated by a prescribed control program that initiates the self-testing and/or self-calibration.
When an operations amplifier is employed, the temperature coefficient can be simply adjusted by means of a voltage divider. To compensate the temperature coefficient, at least one resistor is variable. This can be accomplished by, for instance, varying the feedback resistance with additional parallel resistors. The parallel circuit can be represented by programmable resistance networks or current networks. Since the MOS switches employed during calibration are not ideal, however, but have a finite ON resistance, it is simple to detect the situation with two MOS switches in parallel. The effect of the switches can then be determined to advantage by calculation.
Especially appropriate for this compensation is an embodiment of the present invention using operations amplifiers to switch a band-gap reference source. The same circuitry is appropriate for use with low battery voltage.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a band-gap voltage reference.
FIG. 2 illustrates an operations amplifier with negative feedback.
FIG. 3 illustrates another circuit diagram of the operations amplifier.
FIG. 4 illustrates a third circuit diagram of the operations amplifier.
FIG. 5 illustrates the total circuitry involved in an embodiment of the present invention.
FIG. 6 is a flowchart.
FIG. 7 is another flowchart.
FIG. 8 is yet another flowchart.
DETAILED DESCRIPTION
FIG. 1 illustrates a voltage reference in the form of a band gap reference. Band-gap voltage-reference sources are in themselves known. They basically employ the forward voltage in a diode or the base-emitter voltage of a bipolar transistor as the voltage reference. The drawback of this reference voltage, however, when working with silicon bipolar transistors, is that it can have a temperature coefficient of approximately -2 mV/K. The circuits are accordingly designed to compensate the negative temperature coefficient with a positive coefficient of the same size. The operations amplifier 1 illustrated FIG. 1 is supplied from a current-level circuit in the form of two bipolar transistors T1 and T2, of the npn conductivity type for example. There is a voltage divider with resistors R1 and R2 in the emitter-current path of transistor T2. The middle tap of the voltage divider extends to the node 2 at the non-inverting input terminal (+) of operations amplifier 1. There is a resistor R3 in the emitter-current path of transistor T1. Resistor R3 extends to the node 3 at the inverting input terminal (-) of operations amplifier 1. The circuit is provided with supply voltage V.sub.
REFERENCES:
patent: 5229710 (1993-07-01), Kraus et al.
patent: 5247241 (1993-09-01), Ueda
Patel Rajnikant B.
Robert & Bosch GmbH
Wong Peter S.
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