Claims:
1. A phase shifter apparatus for generating one or more output signals, the phase shifter apparatus comprising:
a filter 302 configured to receive at least one input signal and generate said one or more output signals, at least one of said output signals having a variable phase difference;
a phase detector 308 configured to receive the at least one input signal received at the filter, the at least one output signal having said variable phase difference, and obtain a phase shifted difference signal based on the at least one input signal received and the at least one output signal using a low pass ?lter;
a microcontroller based device 306 configured to amplify the phase shifted difference signal obtained by the phase detector to generate at least a control voltage; and
wherein the filter 302 is further configured to receive the control voltage generated by the microcontroller based device to maintain a phase shift of the at least one input signal constant over a de?ned frequency range based at least on the the received control voltage.

2. The phase shifter apparatus as claimed in claim 1, wherein the phase detector 308 comprises of an analog multiplexer 312.

3. The phase shifter apparatus as claimed in claim 1, wherein the filter 302 comprises a signal processing circuit.

4. The phase shifter apparatus as claimed in claim 1, wherein the filter 302 comprises a junction gate field-effect transistor (JFET) 304.

5. The phase shifter apparatus as claimed in claim 1, wherein the filter 302 comprises a voltage-controlled resistor (VCR).

6. The phase shifter apparatus as claimed in claim 1, wherein the microcontroller based device 306 is configured to:
determine a difference between the phase shifted difference signal and a set reference voltage to generate at least a phase shift value, wherein the phase shift value is fed to the filter;
find error signal in the phase shifted difference signal; and
provide a proportional control signal based on the phase shifted difference signal and/or the set reference voltage.

7. The phase shifter apparatus as claimed in claim 1, wherein the phase shift of the at least one input signal is maintained by varying a gate-source voltage and a drain-source resistance of the at least one input signal.

8. The phase shifter apparatus as claimed in claim 1, wherein the phase shift of the at least one input signal is maintained by controlling a gate-source voltage and a drain-source resistance of the at least one input signal.

9. A phase shifter apparatus for generating one or more output signals, comprising:
an operational amplifier (OPAMP) having at least a junction gate field-effect transistor (JFET) to receive a control voltage generated by a microcontroller based device to maintain a phase shift of at least one input signal constant over a de?ned frequency range based at least on the the received control voltage.

10. The phase shifter apparatus as claimed in claim 9, wherein the microcontroller based device comprises:
a differential amplifier to determine a difference between a phase shifted difference signal and a set reference voltage to generate at least a phase shift value, wherein the phase shift value is fed to the OPAMP;
a simple negative feedback system with error detection to find error signal in the phase shifted difference signal; and
a proportion controller to provide a proportional control signal based on the phase shifted difference signal and/or the set reference voltage.

, Description:
TECHNICAL FIELD
[0001] The present disclosure relates to a phase shifter, and more specifically relates to, controller implementation of frequency independent phase shifter to keep a phase shift of an input constant over a de?ned frequency range.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] In general, a phase shifter changes the phase of the output signal in relation to the input signal. Phase shifts have numerous uses including, but not limited to, phase discriminators, beam forming networks, power dividers, linearization of power amplifiers, phased array antennas, and electronically steered antennas.
[0004] Electronic phase shifter circuits are used to change the transmission phase angle of a signal, and are commonly used to phase shift radio frequency (RF) signals. Modern phase shifter circuits may be digitally controlled and thus provide a discrete set of phase states that are selected by a binary control word. Some phase shifter circuits also include a digitally controlled RF signal attenuator circuit that provides a discrete set of attenuation states that are selected by a binary control word. It is well known that obtaining phase shift circuits that are insensitive to frequency is difficult.
[0005] Efforts have been made in related art to address above stated problem by using phase shifters. An example of such phase shifters is recited in United States patent application 5038115A, entitled “Method and apparatus for frequency independent phase tracking of input signals in receiving systems and the like”. The patent discloses an output signal of a phase tracking system maintains phase coherence with the dominant input signal while tracking the frequency of that same dominant input signal without additional phase shifting circuitry. Circuitry having a second phase locked loop is added to a conventional phase locked loop to form a phase tracking system which provides a precisely constant phase shift over a full range of frequencies of the signal captured by the conventional phase locked loop. Another example of such phase shifters is recited in United States patent application 4682128A, entitled “Phase shifter”. The patent discloses a phase shifter with a phase shift primarily independent of frequency includes first and second quadrature hybrids, a delay and a ganged switch. A first path includes an input into the delay, the delay output being connected into the first quadrature hybrid. The corresponding isolated terminal of the first quadrature hybrid forms the output of the first path. A second path includes an input to the second hybrid quadrature with a terminal thereof as an output. Two remaining terminals of the second quadrature hybrid are taken to a common ground through two capacitors of preselected value. The ganged switch selectively engages a system input to either the inputs of the first path or the second path and simultaneously engages a system output to the outputs of the first path or the second path.
[0006] A phase shifter is a system that produces a precise desired phase shift of the input signal. The phase shifter ?nds many applications in communication and control systems and they require the phase shift to be constant even though the frequency is varied. Usually the phase shifter circuit is implemented using all pass ?lter, which could be active or passive. However, in the conventional phase shifter setup, as the frequency varies the phase shift will also vary. Further, there is no system and method that keeps the phase shift of the input constant over a de?ned frequency range.
[0007] Thus, there still exists a need to provide an efficient, effective, reliable and improved controller (microcontroller / microprocessor based phase shifter) having an implementation of frequency independent phase shifter to keep a phase shift of an input constant over a de?ned frequency range. Further, there exists a need of a system and method that keeps the phase shift of the input constant over a de?ned frequency range.
[0008] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0009] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about”. Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[00010] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[00011] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[00012] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

SUMMARY
[00013] The present disclosure relates to a phase shifter, and more specifically relates to, controller implementation of frequency independent phase shifter to keep a phase shift of an input constant over a de?ned frequency range.
[00014] Accordingly, an aspect of the present disclosure relates to a phase shifter apparatus for generating one or more output signals. The phase shifter includes a filter, a phase detector and a microcontroller based device. The filter receives at least one input signal and generate said one or more output signals, at least one of said output signals having a variable phase difference. The phase detector receives at least one input signal received at the filter, the at least one output signal having said variable phase difference, and obtain a phase shifted difference signal based on the at least one input signal received and the at least one output signal using a low pass ?lter. The microcontroller based device amplifies the phase shifted difference signal obtained by the phase detector to generate at least a control voltage. The filter receives the control voltage generated by the microcontroller based device to maintain a phase shift of the at least one input signal constant over a de?ned frequency range based at least on the the received control voltage.
[00015] In an aspect, the phase detector includes an analog multiplexer.
[00016] In an aspect, the filter includes a signal processing circuit.
[00017] In an aspect, the filter includes a junction gate field-effect transistor (JFET).
[00018] In an aspect, the filter includes a voltage-controlled resistor (VCR).
[00019] In an aspect, the microcontroller based device includes a differential amplifier, simple negative feedback system and a proportion controller. The differential amplifier determines a difference between the phases shifted difference signal and a set reference voltage to generate at least a phase shift value, wherein the phase shift value is fed to the filter. The simple negative feedback system with error detection to find error signal in the phase shifted difference signal; and a proportion controller to provide a proportional control signal based on the phase shifted difference signal and/or the set reference voltage.
[00020] In an aspect, the phase shift of the at least one input signal is maintained by varying a gate-source voltage and a drain-source resistance of the at least one input signal.
[00021] In an aspect, the phase shift of the at least one input signal is maintained by controlling a gate-source voltage and a drain-source resistance of the at least one input signal.
[00022] An aspect of the present disclosure relates to a phase shifter apparatus for generating one or more output signals. The phase shifter includes an operational amplifier (OPAMP) having at least a junction gate field-effect transistor (JFET) to receive a control voltage generated by a microcontroller based device to maintain a phase shift of at least one input signal constant over a de?ned frequency range based at least on the the received control voltage.
[00023] In an aspect, the microcontroller based device includes a differential amplifier, simple negative feedback system and a proportion controller. The differential amplifier determines a difference between the phases shifted difference signal and a set reference voltage to generate at least a phase shift value, wherein the phase shift value is fed to the filter. The simple negative feedback system with error detection to find error signal in the phase shifted difference signal; and a proportion controller to provide a proportional control signal based on the phase shifted difference signal and/or the set reference voltage.
[00024] Existing systems are analog systems and analog systems have dependency on environmental factors like temperature. Also, analog systems are prone to error due to tolerances. This is where a need of microcontroller / microprocessor based phase shifter i.e., the present invention arises. The present invention (implemented in the form of microcontroller/microprocessor) enables to can bring precision and its output is not prone to error due to factors like temperature. Also present invention offers a lot of flexibility in terms of interface to choose value of phase shift. User can provide input using digital keys, analog potentiometers or it can be remotely configured over communication channel.
[00025] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[00026] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. The diagrams are for illustration only, which thus is not a limitation of the present disclosure, and wherein:
[00027] FIG. 1 is circuit diagram of an all pass filter, in accordance with an exemplary embodiment of the present disclosure.
[00028] FIG. 2 is circuit diagram of Voltage Controlled Resistor using JFET along with linearization circuit, in accordance with an exemplary embodiment of the present disclosure.
[00029] FIG. 3 illustrates an exemplary block diagram of a proposed phase shifter apparatus, in accordance with an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION
[00030] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the present disclosure as defined by the appended claims.
[00031] If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[00032] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[00033] Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. These exemplary embodiments are provided only for illustrative purposes and so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those of ordinary skill in the art. The invention disclosed may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Various modifications will be readily apparent to persons skilled in the art. The general principles defined herein may be applied to other embodiments and applications without departing from the scope of the invention. Moreover, all statements herein reciting embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure). Also, the terminology and phraseology used is for the purpose of describing exemplary embodiments and should not be considered limiting. Thus, the present invention is to be accorded the widest scope encompassing numerous alternatives, modifications and equivalents consistent with the principles and features disclosed. For purpose of clarity, details relating to technical material that is known in the technical fields related to the invention have not been described in detail so as not to unnecessarily obscure the present invention.
[00034] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[00035] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[00036] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[00037] The present disclosure relates to a phase shifter, and more specifically relates to, controller implementation of frequency independent phase shifter to keep a phase shift of an input constant over a de?ned frequency range.
[00038] However, in the conventional phase shifter setup, as the frequency varies the phase shift will also vary. Further, there is no system and method that keeps the phase shift of the input constant over a de?ned frequency range.
[00039] The present invention provides controller implementation of frequency independent phase shifter to keep a phase shift of an input constant over a de?ned frequency range. The proposed invention provides a system and method that keeps the phase shift of the input constant over a de?ned frequency range.
[00040] A phase shifter is a system, which can produce a precise desired phase shift of the input signal. The phase shifter ?nds many applications in communication and control systems and they require the phase shift to be constant even though the frequency is varied. Usually the phase shifter circuit is implemented using all pass ?lter, which could be active or passive. In the phase shifter setup, as the frequency varies, the phase shift will also vary. Thus to make a system which produces the desired phase shift independent of frequency, the proposed system is supposed to vary either the capacitor value or the resistor value. The proposed system has controlled resistor value by using a JFET. The gate voltage of the JFET needs can be controlled based on the di?erence between the desired and actual phase shift. To do this there is a requirement of a negative feedback system with proportion control to be implemented.
[00041] An aspect of the present disclosure relates to a system and method that keeps the phase shift of the input constant over a de?ned frequency range.
[00042] In an aspect, phase of the output signal is required to be measured for the feedback connection. A phase detector can include an analog multiplexer. The analog multiplexer fed with input signal and phase-shifted output, followed by a low pass ?lter will be capable of providing a DC equivalent measure of phase shift. A simple negative feedback system with error detection and proportion controller implemented using a difference ampli?er [controller (microcontroller)] can be able to provide the control voltage, which is to be fed to gate of the JFET required for this system. By varying the gate-source voltage, the drain-source resistance can be controlled. The relationship between gate-source voltage and drain-source resistance is dependent on device parameters.
[00043] FIG. 1 is circuit diagram of an all pass filter, in accordance with an exemplary embodiment of the present disclosure. FIG. 2 is circuit diagram of Voltage Controlled Resistor using JFET along with linearization circuit, in accordance with an exemplary embodiment of the present disclosure.
[00044] As shown in FIG.1, an all pass ?lter can be a signal processing circuit, which has unity gain, but the phase is a function of the frequency. Usual applications of all pass ?lter are to compensate for the undesired phase shift that can be caused while signal is passing through a system.
The transfer function for the all pass ?lter is given as,
H(s) = (sRC – 1)/(sRC + 1)
The magnitude is given by,
|H(s)| = 1
And phase response of the same is given as
< H(s) = p - 2 arctan (wRC)
[00045] The phase shift is a function of the resistor and capacitor value as well as the frequency. So by varying the resistor or capacitor, the variation due to frequency can be compensated. Thus as shown in circuit, the R1 can replace at the non-inverting terminal by using JFET to work as a variable resistor.
[00046] As shown in FIG.2, for a junction ?eld-effect transistor (JFET) under certain operating conditions, the resistance of the drain-source channel is a function of the gate-source voltage alone and the JFET will behave as an almost as a pure ohmic resistor. Maximum drain-source current, I DSS, and minimum resistance r RDS (on), can exist. When the gate-source voltage is equal to zero volts (V GS = 0). If the gate voltage is increased (negatively for n-channel JFETs and positively for p-channel), the resistance can also increase. When the drain current can be reduced to a point where the FET is no longer conductive, the maximum resistance is reached. The voltage at this point is referred to as the pinchoff or cutoff voltage and is symbolized by V GS = V GS (off). Thus, the device functions as a voltage- controlled resistor. In the proposed system, an N-channel JFET BFW10 can be used which has negative value of VGS. The channel width can be increased or decreased by varying the V GS values. Hence, the channel resistance varies. For different values of V GS (<0V) different values of resistance between drain and source can be achieved and thus the proposed concept can be used in all pass ?lter to get different phase shift between input and output by replacing resistor with JFET. In Ohmic region as V DS increases, non-linearity in the graph increases with more negative pinch off voltage and even if the V GS is constant the drain to source resistance R DS will change which generates an error which has to be minimized. The proposed system can use a feedback network to overcome this problem which makes the JFET to operate linearly. Feedback can be given by connecting feedback resistor from drain to gate. If there is a positive increment in the drain to gate voltage can cause in increment the gate voltage. If there is negative voltage at the drain to gate, it causes to decrease the drain current and again linearization can be achieved.

Finding JFET resistances
[00047] FIG. 3 illustrates an exemplary block diagram of a proposed phase shifter apparatus, in accordance with an exemplary embodiment of the present disclosure.
[00048] As shown in FIG. 3, the phase detector can include an analog multiplexer 302, fed with input signal and phase-shifted output, followed by a low pass ?lter 304. The low pass filter can be capable of providing a DC equivalent measure of phase shift. The literature survey helped to uncover that a simple negative feedback system with error detection and proportion controller implemented using a controller (microcontroller) 306 can be able to provide the control voltage, which is to be fed to gate of the JFET required for this system. The idea of using a JFET as a voltage-controlled resistor (VCR) 308 can also note during the survey. By varying the gate-source voltage, the drain-source resistance can be controlled. The relationship between gate-source voltage and drain-source resistance is dependent on device parameters. As a result, for application like here where system may have terminal voltage with 1V peak to peak, we need to use a linearization circuit.
[00049] In another embodiment, a phase detector 310 simply produces an output that is proportional to the phase difference between the two signals. When the phase difference between the two incoming signals is steady, it produces a constant voltage. When there is a varying phase difference between the two signals, it produces a varying voltage. The original input signal is passed through a comparator and output of the comparator acts as a control input of the analog switch IC CD4066. The phase shifted version of the original input signal is multiplexed using comparator output in alternative succession and multiplexed output is given at the input of the low pass ?lter 304. Thus, different values of the phase shift between two signals can correspond to different DC voltage levels. The input sampled from the analog multiplexer 302 gives the equivalent DC value at the output of low pass ?lter 304; this DC value represents the amount of phase shift. For example, if phase shift is 90 degree then output of low pass ?lter is 0 V.
[00050] In another embodiment, the control circuit 306 usually is designed using only hardware components; in present innovation a microcontroller can achieve intelligent control with greater accuracy. In an exemplary embodiment, the controller (microcontroller) 306 can be used as control circuit.
[00051] In another embodiment, the control circuit plays two roles in the feedback system, ?rst to ?nd the error signal and then to provide a proportional control signal. The controller (microcontroller) 306 can ?nd differences between the phase equivalent DC signal coming from phase detector 310 and the set reference voltage. This difference can be ampli?ed and given to the gate of the JFET 308. For a better control, the gain of the ampli?er is kept very large(x470).
[00052] In another embodiment, simplest linearization circuit for JFET to derive drain resistance, simplest OPAMP based circuitry can be used to achieve linearization
[00053] In another embodiment, simplest control circuit can achieve feedback and derive control signal and error signal. Programmable R and C can be achieved through control circuit modification to occupy larger band of constant phase shift.
[00054] It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refers to at least one of something selected from the group consisting of A, B, C ….and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc. The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the scope of the appended claims.
[00055] While embodiments of the present disclosure have been illustrated and described, it will be clear that the disclosure is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to those skilled in the art, without departing from the scope of the disclosure, as described in the claims.
[00056] In the description of the present specification, reference to the term "one embodiment," "an embodiments", "an example", "an instance", or "some examples" and the description is meant in connection with the embodiment or example described The particular feature, structure, material, or characteristic included in the present invention, at least one embodiment or example. In the present specification, the term of the above schematic representation is not necessarily for the same embodiment or example. Furthermore, the particular features structures, materials, or characteristics described in any one or more embodiments or examples in proper manner. Moreover, those skilled in the art can be described in the specification of different embodiments or examples are joined and combinations thereof.
[00057] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.
[00058] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
[00059] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
[00060] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.