Reference voltage generator with monitoring and start up means

Details Reference voltage generator with monitoring and start up means Reference voltage generator with monitoring and start up means

2000-06-20

2001-03-20

Nguyen, Matthew (Department: 2838)

Electricity: power supply or regulation systems

Self-regulating

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

Reexamination Certificate

active

06204653

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a voltage reference generator as is described in the preamble of the first claim.
Such a voltage reference generator is already known in the art, e.g. from the tutorial handbook “
Analysis and design of analogue integrated circuits
” of Paul R. Gray and Robert G. Meyer, John Wiley and Sons, New-York (1993). Therein on page 344, FIG. 4.49c, a bandgap reference circuit is shown, including an operational amplifier which relates to the operational amplifier means as described in the preamble of the first claim of the present document, associated in a feedback loop to a circuit consisting of the transistors Q
1
,Q
2
, and resistors R
1
,R
2
and R
3
, corresponding to the feedback circuit, as well described in the preamble of the first claim of this document.
Such a configuration, as indicated by this prior art document on the same page, generates at its output terminal a reference voltage, but needs appropriate start-up circuitry in order to insure a stable operation point. The latter condition is of course necessary to ensure that the output voltage is the correct one. However, even in the presence of such a start-up circuit, some transients in the output voltage may occur and the output voltage can have the wrong value. Additional circuits relying on the voltage reference output voltage can thereby malfunction seriously and create erroneous or even hazardous situations. Examples are circuits for accurate analog power-on-reset functions for low supply level conditions, charging circuits for very sensitive Lithium-Ion batteries that need a very precise voltage limitation, circuits for generation of precise supply voltage levels using low drop-out regulators, etc.
At the same time, in applications where this voltage regulator is part of an integrated circuit, the total configuration needs to be as simple as possible because of cost and power consumption issues. This is for instance the case when the aforementioned applications are used in a GSM-chip.
SUMMARY OF THE INVENTION
An object of the present invention is thus to provide a voltage reference generator of the above known kind, but which solves the aforementioned problems.
According to the invention, this object is obtained by the fact that the voltage reference generator further includes monitoring as well as start-up means in the configuration described by the characteristic portion of the first claim.
By the fact that the start-up means is controlled itself by an output signal generated by the monitoring means, such that the complete configuration thereby provides an additional feedback of the reference output voltage signal to an input of the operational amplifier means itself, a self-sustaining stable system is obtained. At the same time the second output terminal of the monitoring means provides a validation flag indicative of the correct and reliable operation of the voltage reference generator, which can thus be interpreted by further circuitry. The total voltage reference generator thereby remains of a very low complexity, since only two additional blocks are added, which, as will be explained in a further paragraph of this document, can each be very simple.
Another characteristic feature of the present invention is described in claim
2
.
In this way, by simultaneously monitoring two parameters of the operational amplifier means, a better, more accurate and full-proof indication of the correctness of the operation is obtained compared to the case where only one single parameter is monitored.
Still a further characteristic feature of the present invention is described in claim
3
.
The second parameter thus consists of a current flowing through an output stage of the operational amplifier means. Comparison of this value with a predetermined threshold current level, results in a first authorisation flag, being an internal signal of said monitoring means. Thereby a first indication of the correct operation of the circuit is provided.
Yet another characteristic feature of the present invention is described in claim
4
.
Similarly, the reference output voltage is compared to a predetermined threshold voltage level within a voltage monitoring means. This results in a second indication of the correct operation of the circuit.
Furthermore, referring to claim
5
, an AND-type means is a simple means for guaranteeing that both authorisation flags simultaneously have to comply to certain values, such that an unambiguous validation flag is provided to the second output terminal of the voltage reference generator.
Another characteristic feature of the present invention is described in claim
6
.
Thereby a simple embodiment of the aforementioned voltage monitoring means is described. It is important to notice that when the resultant output voltage is high, a high enough value of the reference output voltage is present. In this case an autonomous evolution of the internal voltage reference circuit, consisting of the operational amplifier means and the feedback circuit, towards the only correct table operating point is guaranteed, and a further regulation by the start-up means is inhibited. In the other case, when the resultant output voltage is low, the start-up means remains activated in order to force the internal voltage reference circuit towards its stable operating point.
In this respect the value of the predetermined threshold voltage level with which the reference output voltage is compared, is a design parameter related to the stable operating point, as is stated in claim
7
. This will also be further explained in the descriptive part of this document.
Yet a further characteristic feature of the present invention is described in claim
8
.
This presents a very simple embodiment of such a start-up means, reducing the cost of the overall voltage reference generator.
Other characteristic features of the present invention are described in claims
9
,
10
and
11
.
The output stage of the operational amplifier means and the current monitoring means are thereby similar in structure, consisting of a current source in series with an active element, for instance a transistor. Both transistors are grounded and controlled by the same signal, which is delivered at the second output terminal of the operational amplifier means. By designing the transistors of the output stage and the current monitor such that their current ratio equals th ratio of a first current and a second current, this first current being related to the current supplied by the first current source, this second current being the current delivered by the second current source, the current comparison function of the current monitor means is obtained. Indeed, the current monitor means has to check whether the current flowing through the output stage exceeds a predetermined threshold current level. This current flowing through the output stage is the current that flows when the first transistor is on. The first current is thereby equal to the current delivered by the first current source, minus the current delivered to the feedback circuit, in the stable operating region, and minus a predetermined current to a load. When the first transistor is on, it will thus carry the first current. Since the first and second transistors both receive the same driving signal, and since the ratios of their currents match with the ratio of the first and second currents, the output of the current monitor indicates whether the first current is sunk by the first transistor, thereby thus providing the current comparison function envisaged.


REFERENCES:
patent: 4609833 (1986-09-01), Guterman
patent: 5751142 (1998-05-01), Dosho et al.
patent: 5773967 (1998-06-01), Tenten
patent: 5789906 (1998-08-01), Mizuide
patent: 5867013 (1999-02-01), Yu
patent: 5955873 (1999-09-01), Maccarrone et al.
patent: 0 714 055 A1 (1996-05-01), None
patent: 0 840 193 A1 (1998-05-01), None
“Analysis and design of analogue integrated circuits” of Paul R. Gray and Robert G. Meyer, John Wiley and Sons, New York (1993).

Affiliated with

Also associated with

Rating

Reference voltage generator with monitoring and start up means does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Reference voltage generator with monitoring and start up means, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Reference voltage generator with monitoring and start up means will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2454176