The present invention provides circuits, systems, and methods for programming a floating gate. As described herein, a floating gate tunneling device is used with an analog comparison device in a circuit having a floating reference node and an offset-mitigating feedback loop for iteratively programming a floating gate or multiple floating gates.
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1. A circuit configured to place a selected charge on a floating gate of a tunneling device, said circuit comprising:
an analog comparison device operatively coupled to said tunneling device;
a reference node operatively coupled to said tunneling device; and
a feedback loop configured to couple an output of said analog comparison device to an input of said analog comparison device.
14. A circuit configured to place a selected charge on a floating gate of a tunneling device, said circuit comprising:
an analog comparison device operatively coupled to said tunneling device, wherein said analog comparison device has a first input configured to receive a reference signal;
a feedback loop configured to couple an output of said analog comparison device to a second input of said analog comparison device;
a reference node operatively coupled to said tunneling device; and
a voltage level shifting device selectably coupled to said tunneling device.
0. 19. A circuit for placing a selected charge on the floating gate of a tunneling device, comprising:
an analog comparing device having a first input operably coupled to the output of a tunneling device, the analog comparing device also having a second input selectably coupled to a reference signal;
a level shifting device selectably coupled to the input of the tunneling device, the voltage level shifting device also operably coupled to receive input from an analog comparing device output;
wherein the input of the tunneling device is selectably coupled to a reference node; and wherein a selected charge provided by the reference signal is placed on the floating gate of the tunneling device.
0. 20. A method for programming a floating gate circuit comprising the steps of:
using a level shifting device operably coupled to an analog comparing device output, providing a voltage to a tunneling device, the voltage of sufficient magnitude to induce tunneling in the tunneling device, whereby a floating reference signal is conducted through the tunneling device, the floating reference signal in turn causing a first input signal at a first analog comparing device input to rise;
providing a second input signal to a second input of the analog comparing device until the first and second input signals become equal, whereby the analog comparing device output to the input of the level shifting device decreases, whereby the voltage at the tunneling device is changed to a level insufficient to maintain tunneling in the tunneling device; and
causing the analog comparing device to reverse polarity, thereby placing the analog comparing device in unity gain mode, whereby the analog comparing device output, and thus the output of the floating gate circuit, is programmed at the reference signal value.
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This application is a continuation application of application Ser. No. 13/327,364 filed Dec. 15, 2011, which is a divisional application of application Ser. No. 12/363,232 filed Jan. 30, 2009, now U.S. Pat. No. 7,859,911, which claims priority to Provisional Patent Application Ser. No. 61/082,403 filed on Jul. 21, 2008, all of which are incorporated herein by reference in their entireties. This application and the parent applications have at least one common inventor.
The invention relates to low-current analog integrated circuitry. More particularly, the invention relates to microelectronic floating gate circuit architectures, systems, and methods for their programming and operation.
Programmable analog circuits are often required in applications where voltage accuracy and low power use are desirable traits.
Band gap reference voltage circuits are frequently used in applications that require a high degree of voltage accuracy. Band gap voltage reference circuits are known for their capabilities for providing excellent accuracy and stability over time and a range of operating temperatures. Unfortunately, however, band gap references are limited to a fixed voltage level, typically about 1.2V. The additional circuitry required for providing other voltage levels, such as fixed gain amplifiers for example, can be seriously detrimental to accuracy. Additionally, band gap voltage reference circuits generally draw a significant amount of power, presenting an additional problem in applications in which low power consumption is desirable.
Floating gate voltage reference circuits are often chosen for their low power requirements, but can be problematic in applications requiring a high degree of accuracy in providing a selected programmed voltage level, particularly over time and changes in temperature. A floating gate may be conceptualized as a charge oasis of conductive material electrically isolated from the outside world by a semiconductor substrate desert. The floating gate is capacitively coupled to the substrate or to other conductive layers. The floating gate is usually used to provide bias to the gate of a transistor and is readable without causing a significant leakage of charge. In theory, a floating gate programmed at a particular charge level remains at that level permanently, since the floating gate is insulated by the surrounding material. The floating gate is commonly charged using Fowler-Nordheim tunneling, or Channel Hot Carrier (CHC) tunneling, practices generally known to practitioners of the microelectronic arts. The accuracy of common floating gate circuits is limited for at least two primary reasons. Firstly, the potential on a floating gate decreases after it is programmed due to the capacitance inherent in the tunneling device. This voltage offset is well-defined and predictable, but is unavoidable in prior art floating gate voltage reference circuits because the capacitance of the tunneling device cannot be completely eliminated. Secondly, the accuracy of prior art floating gate voltage reference circuits is also hampered by the decay of the theoretically permanent charge on the floating gate over time. The decay of the charge over time occurs due to various factors, including the gradual escape of electrons from the tunneling device, and dielectric relaxation of the floating gate capacitors. The decay of charge is not entirely predictable since it can be influenced by environmental factors such as mechanical and thermal stress effects or other variables.
Due to these and other problems and potential problems, improved floating gate reference and feedback circuits would be useful and advantageous in the arts. Floating gate circuit architecture and associated methods adapted to rapid and accurate offset compensation would be particularly beneficial contributions to the art.
In carrying out the principles of the present invention, in accordance with preferred embodiments, the invention provides advances in the arts with novel methods directed to providing low-current floating gate architectures with offset mitigation capabilities and improved accuracy.
According to aspects of the invention, preferred embodiments of floating gate circuit methods use an iterative floating gate device and floating reference node programming technique for improved accuracy and stability.
According to one aspect of the invention, a preferred embodiment includes method steps for programming a floating gate circuit using a tunneling device and a floating reference node for iteratively programming an output with an offset-mitigating feedback loop.
According to another aspect of the invention, a preferred embodiment thereof includes the step of operating a suitably equipped circuit in a tunneling mode whereby charge is added to a tunneling device and conducted to a first op amp input such that the first op amp input voltage becomes equal with a second op amp input reference voltage. In a further step the op amp inputs are reversed for operating the op amp in a unity gain mode such that the output of the circuit is substantially equal to the reference voltage.
According to another aspect of the invention, a preferred embodiment thereof includes using the steps for programming a plurality of floating gates.
According to yet another aspect of the invention, a preferred embodiment includes the steps of monitoring the output of the circuit, and based on a comparison of the circuit output with a preselected tolerance threshold, selectably reiterating the tunneling mode step and the unity gain mode step using an incrementally changed reference voltage.
The invention has advantages including but not limited to providing one or more of the following features; improved accuracy, rapid programming, improved stability over a range of operating conditions, and efficient, ultra-low power requirements. These and other advantageous features and benefits of the present invention can be understood by one of ordinary skill in the arts upon careful consideration of the detailed description of representative embodiments of the invention in connection with the accompanying drawings.
The present invention will be more clearly understood from consideration of the following detailed description and drawings in which:
References in the detailed description correspond to like references in the various drawings unless otherwise noted. Descriptive and directional terms used in the written description such as front, back, top, bottom, upper, side, et cetera, refer to the drawings themselves as laid out on the paper and not to physical limitations of the invention unless specifically noted. The drawings are not to scale, and some features of embodiments shown and discussed are simplified or amplified for illustrating principles and features, as well as anticipated and unanticipated advantages of the invention.
While the making and using of various exemplary embodiments of the invention are discussed herein, it should be appreciated that the present invention provides inventive concepts which can be embodied in a wide variety of specific contexts. It should be understood that the invention may be practiced with various electronic circuits, microelectronic circuit components, systems, system components, and subsystems without altering the principles of the invention. For purposes of clarity, detailed descriptions of functions, components, and systems familiar to those skilled in the applicable arts are not included. In general, the invention provides programmable analog voltage reference circuits for rapidly and accurately setting an output to a given selected voltage.
Now referring primarily to
The circuit arrangement shown in
The AMPOUTPUT voltage is preferably monitored using suitable techniques known in the arts, and in the event a selected voltage level is not present within in acceptable tolerances, e.g., the AMPOUTPUT voltage is too low due to non-ideal behavior of the circuit, the process described above may be reiterated with the modification that the reference voltage VREF may be increased, which in turn results in an increased voltage at the floating reference node 20, and ultimately increased voltage at AMPOUTPUT. Using the circuits and techniques of the invention, the AMPOUTPUT voltage can be rapidly adjusted to approach a selected value within precise tolerances by using successive iterations of the steps shown and described. The programmed floating gate may be erased to reset the circuit by raising the voltage at C0, energizing the trapped electrons in the floating gate to an energy level sufficient to enable them to escape.
Various implementations of the invention are possible, and all variations of potential embodiments cannot, and need not, be shown herein. Although specific exemplary embodiments using representative component parts are shown for the purposes of illustration, some elements of the circuit may be substituted without undue experimentation by those skilled in the arts. For instance, analog comparison devices such as analog to digital converter (ADC) devices or comparators may be used in place of op amps, level shifter topology may be implemented in various ways, and suitable modifications may be made to adapt the circuit for current, power, transconductance, or other inputs and/or outputs. The invention may be used, for example, in power systems, energy systems, portable electronics, battery and power supply management systems, and the like. An example of a preferred embodiment is shown in
The steps described may be reiterated one or more times as needed in order to approach the desired voltage level within a selected degree of accuracy, although it is believed that in general few iterations are required for most applications. It should be understood by those skilled in the arts that the circuit and components shown are representative of one example of an embodiment of the circuitry and methods of the invention for illustrative purposes and are not exclusive, restrictive, or limiting, as to the potential implementations and uses of the invention. For example, those skilled in the arts will appreciate that the floating gate circuit architecture and offset cancellation methods may be used in a wide variety of contexts for managing offsets of electronic signals such as voltage, current, impedance, and the like.
An alternative depiction of steps in methods of programming circuits using floating gate devices according to the invention is shown in
An alternative approach to programming a floating gate for practicing the invention is shown in
The methods and apparatus of the invention provide one or more advantages including but not limited to, speed, accuracy, offset compensation, and efficiency in programmable analog circuits. While the invention has been described with reference to certain illustrative embodiments, those described herein are not intended to be construed in a limiting sense. For example, variations or combinations of steps or materials in the embodiments shown and described may be used in particular cases without departure from the invention. Various modifications and combinations of the illustrative embodiments as well as other advantages and embodiments of the invention will be apparent to persons skilled in the arts upon reference to the drawings, description, and claims.
Smith, Brett, Teggatz, Ross E, Chen, Wayne T, Blackall, Erick
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