Static information storage and retrieval – Read/write circuit – Including signal comparison
Reexamination Certificate
1999-12-30
2001-08-14
Nelms, David (Department: 2818)
Static information storage and retrieval
Read/write circuit
Including signal comparison
C327S512000
Reexamination Certificate
active
06275422
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to integrated circuits. In particular, the present invention relates to constant voltage and current generators in integrated circuits.
BACKGROUND OF THE INVENTION
Constant voltage and current generators are used in many different ways in integrated circuits. For instance, constant voltages and currents are used as references to accurately generate various signals and to measure various parameters within integrated circuits. Flash electrically erasable programmable read only memory (EEPROM) is one example of an integrated circuit technology that often relies on constant voltage generation. Other examples include analog to digital converts, digital to analog converts, and virtually any precision analog circuit.
In flash EEPROM, cells of memory are erased using a relatively large voltage compared to voltage levels normally available in integrated circuits. For instance, a normally available voltage in an integrated circuit may be 1.55 volts, but cells of flash memory may require 12 volts to erase the cells. A charge pump is used to generate the required 12 volts using the available 1.55 volts. Simply amplifying the available voltage, however, would also amplify any variation in the available voltage. That is, if the available voltage is 1.55 volts plus or minus five percent, the amplified voltage would be 12 volts plus or minus five percent. The voltage needed to erase flash cells often needs to be fairly accurate. If the voltage is too large, it is likely to exceed the break down voltage for the flash cells, potentially causing permanent damage. If the voltage is too small, it may not reliably erase the cells. Whereas a five percent variation on 1.55 voltages may be acceptable, five percent of 12 volts may not be acceptable. Therefore, in order to generate a more accurate voltage, a charge pump relies on a reference voltage provided by a constant voltage generator.
Several types of constant voltage and current generators are known in the art.
FIG. 1
illustrates one example of a constant voltage generator
100
. Operational amplifier
110
is powered by source voltage
170
. Based on source voltage
170
and the voltage differential between the positive and negative terminals, operational amplifier
110
generates reference voltage
120
. The voltage differential between the terminals is equal the voltage differential between nodes
135
and
145
. The voltage differential depends on the voltage through feedback loop
180
(which is reference voltage
120
), resistors
130
and
140
, and diodes
150
and
160
. In other words, as long as source voltage
170
, and the voltages across resistors
130
and
140
, and diodes
150
and
160
, remain constant, reference voltage
120
will remain constant.
Unfortunately, source voltage
170
, the voltage across resistors
130
and
140
, and diodes
150
and
160
, cannot be relied upon to remain constant. For instance, the values change with temperature. The values also change from one integrated circuit to the another due to process variation in manufacturing, especially if two integrated circuits are from different runs of the manufacturing process. As a result, the reference voltage
120
will vary due to temperature variation, process variation, and source voltage variation.
As integrated circuit technology continues to move toward smaller integration, voltage tolerance levels also continue to decrease, making reliable reference signals increasingly more important.
SUMMARY OF THE INVENTION
A signal generator in an integrated circuit includes circuitry to generate an output signal based on a supply signal and a difference between a first reference value and a second reference value. The output signal has an output signal variation due to at least one of a process variation, a temperature variation, and a variation in the supply signal. A first reference device provides the first reference value based on an input signal. A second reference device provides the second reference value based on the input signal. The second reference value can be any one of a plurality of selectable reference values. At least one of the plurality of selectable reference values reduces the output signal variation.
REFERENCES:
patent: 4935914 (1990-06-01), Morita et al.
patent: 5946258 (1999-08-01), Everett et al.
patent: 6055489 (2000-04-01), Beatty et al.
Giduturi Hari
Javanifard Jahanshir J.
Blakely , Sokoloff, Taylor & Zafman LLP
Intel Corporation
Nelms David
Tran M.
LandOfFree
Constant current and voltage method and apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Constant current and voltage method and apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Constant current and voltage method and apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2449628