Abstract:
Systems and methods relating to programmable circuits are described. Several embodiments relate to systems and methods for controlling the long-term stability and accuracy of circuits that produce waveforms varying in frequency and amplitude. Such embodiments may include a circuit comprising a common vacuum environment that houses a pair of heater-thermocouples. The circuit may compare signals outputted by each heater-thermocouple and then may produce a resultant value based on the comparison. The resultant value may be used by the circuit to control the long-term stability and accuracy of the circuit. Such control of the long-term stability and accuracy of the circuit may include drift compensation associated with certain components of the circuit.

Description:
COPYRIGHT 
       [0001]    A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to systems and methods that implement one or more programmable circuits. In particular, but not by way of limitation, the present invention relates to systems and methods for controlling long-term stability and accuracy of circuits that produce waveforms varying in frequency and amplitude. 
       BACKGROUND OF THE INVENTION 
       [0003]    Numerous applications find it useful to control characteristics of output waveforms provided by various types of circuits, especially applications where extreme accuracy and long-term stability is desired or necessary. Critical circuit function in such applications is greatly impacted by variations in component performance. For example, the performance characteristics of amplifiers may vary due to errors resulting from drift of offset and gain. Such errors may restrict the frequency range, impair the accuracy and stability, and slow the response time of circuitry. 
         [0004]    One previously known approach of compensating for errors caused by drift centers upon controlling the entire collection of components in a circuit. This method typically employs circuit designs that use components with exceptional qualities. Unfortunately, an undesirable consequence of this method is increased cost, as components of exceptional quality are generally expensive. An additional consequence of this method is that it relies on careful selection of all components to regulate overall performance of the circuit. As a circuit becomes more complex, the number of components increases, which results in a greater chance of error. While this approach of controlling circuit component selection can compensate for error, it does so without minimizing expense and risk exposure inherent in circuits with many components. 
       SUMMARY OF THE INVENTION 
       [0005]    Exemplary embodiments of the present invention that are shown in the drawings are summarized below. These and other embodiments are more fully described in the Detailed Description section. It is to be understood, however, that there is no intention to limit the invention to the forms described in this Summary of the Invention or in the Detailed Description. One skilled in the art can recognize that there are numerous modifications, equivalents and alternative constructions that fall within the spirit and scope of the invention as expressed in the claims. 
         [0006]    The present invention provides a system and method capable of controlling an output of a circuit. In a first exemplary embodiment, the present invention comprises circuitry operating within a common vacuum environment. The circuitry in one implementation of the first exemplary embodiment comprises two heater-thermocouples. Each heater-thermocouple includes a pair of inputs and a pair of outputs. The heater in a specific heater-thermocouple is connected to the pair of inputs, and the thermocouple in that specific heater-thermocouple is connected to the pair of outputs. 
         [0007]    In another exemplary embodiment, the present invention comprises circuitry including a signal source and a comparator that includes a common vacuum environment. The comparator comprises two inputs, and one output. A signal source produces a source signal, and signals related to the source signal are received by the two inputs. The comparator compares the signals received by the two inputs, and the output produces an output signal based on the comparison. The signal source operates on the output signal in order to adjust the output signal. 
         [0008]    As previously stated, the above-described embodiments and implementations are for illustration purposes only. Numerous other embodiments, implementations, and details of the invention are easily recognized by those of skill in the art from the following descriptions and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Various objects and advantages and a more complete understanding of the present invention are apparent and more readily appreciated by reference to the following Detailed Description and to the appended claims when taken in conjunction with the accompanying Drawings wherein: 
           [0010]      FIG. 1  depicts a block diagram of a circuit in accordance with one embodiment of the present invention; 
           [0011]      FIG. 2  depicts a block diagram of a circuit in accordance with another embodiment of the present invention; 
           [0012]      FIG. 3  depicts a more-detailed block diagram of the circuitry depicted with respect to  FIG. 2 ; 
           [0013]      FIG. 4  depicts a block diagram of a circuit in accordance with yet another embodiment of the present invention; 
           [0014]      FIG. 5  depicts a more-detailed block diagram of the circuitry depicted with respect to  FIG. 4 ; 
           [0015]      FIG. 6  depicts a block diagram of a circuit in accordance with yet another embodiment of the present invention; and 
           [0016]      FIG. 7  depicts a block diagram of a circuit in accordance with yet another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    One aspect of the present invention contemplates a circuit design that includes a differential heater-thermocouple pair housed within a common vacuum environment. Another aspect of the present invention contemplates a circuit design that compensates for drift in offset and gain of the common vacuum environment and/or one or more other circuit components. Several embodiments of the present invention describe the use of the above two aspects in different circuit designs; however, these embodiments are not intended to be exhaustive of circuit designs capable of employing the above two aspects. 
         [0018]    Referring now to the drawings, where like or similar elements are designated with identical reference numerals throughout the several views, and referring in particular to  FIG. 1 , a block diagram of circuitry  100  in one exemplary embodiment is illustrated. 
         [0019]    As shown, circuitry  100  comprises two heaters  141  and  142 , and two thermocouples  143  and  144 , all of which are housed within a common vacuum environment  145 . As described below, the common vacuum environment  145  is defined by, for example, a single glass envelope (not shown). Heater  141  is thermally connected to thermocouple  143 , thus creating a heater-thermocouple  141 / 143 . Heater  142  is thermally connected to thermocouple  144 , thus creating a heater-thermocouple  142 / 144 . Included in the circuitry  100  are leads  141   a,    141   b,    142   a,    142   b,    143   a,    143   b,    144   a  and  144   b.  Leads  141   a  and  141   b  are connected to heater  141 , and leads  142   a  and  142   b  are connected to heater  142 . Thermocouple  143  is connected electronically to leads  143   a  and  143   b,  and thermocouple  144  is connected electronically to leads  144   a  and  144   b.  In several embodiments leads  141   b,    142   b,    143   b  and  144   b  are connected to ground (not shown); however embodiments of the present invention are by no means limited to such a configuration. 
         [0020]    The vacuum characteristics of the common vacuum environment  145  are advantageous in that the gain of each heater-thermocouple  141 / 143  and  142 / 144  remains relatively constant with respect to the other on a short term basis. If the heater-thermocouples  141 / 143  and  142 / 144  were to be housed in separate glass envelopes (i.e., separate vacuum environments), their gains would likely differ significantly as a function of temperature. Thus, in order to ensure that each heater-thermocouple  141 / 143  and  142 / 144  operates in an identical environment, certain embodiments of the present invention place both pairs in the same evacuated glass envelope. 
         [0021]    In several embodiments of the present invention, other compensation circuitry (not shown) is provided that is not included within the common vacuum environment  145 . In these embodiments, thermocouples  143  and  144  each produce a signal that is released by leads  143   a  and  144   a,  respectively. The produced signals are then operated on by such other circuitry to compensate for long-term drift in the common vacuum environment  145  and/or in one or more additional components in the circuitry. In one of these embodiments, the operation on the signals released by the leads  143   a  and  144   a  is a comparison of those released signals. Based on the comparison, compensation for drift in the common vacuum environment  145  and/or in the one or more additional components may occur. 
         [0022]    It is noted that the use of thermocouples in this embodiment offers a cost effective solution to applications such as true RMS voltage measurement and leveling in many environments over wide temperature ranges; however, the scope and spirit of several embodiments of the present invention is not limited to the implementation of heater-thermocouples. One of skill in the art will appreciate alternatives to using heater-thermocouples while remaining within both the scope and the spirit of the present invention.  100161  Attention is now drawn to  FIG. 2 , which depicts a block diagram of a circuit  200  in accordance with one embodiment of the present invention. As shown, the circuit  200  of  FIG. 2  includes signal sources  210  and  220 , an amplifier  230  and a comparator  240 . 
         [0023]    According to  FIG. 2 , the signal source  210  outputs a signal to the amplifier  230 . The signal outputted by the signal source  210  may be any type of signal at any desired frequency. Once the amplifier  230  receives the signal outputted by the signal source  210 , an amplified signal is outputted by the amplifier  230 . Amplification parameters are described in more detail in the following paragraph. 
         [0024]    The signal source  220  and the comparator  240  are configured to control the amplitude of an output of the circuit  200 . As shown, the comparator  240  receives two signals, including one signal from the signal source  220 , and a feedback signal from the amplifier  230 . The comparator  240  compares these two signals and outputs a signal based on the comparison. The signal outputted by the comparator  240  operates on the amplifier  230  to control the amplification of the signal received by the amplifier  230  from the signal source  210 . The outputted signal of the comparator  240  adjusts the amplification of the amplifier  230  until the two inputs into the comparator  240  are equal or within a specified difference. 
         [0025]    Attention is now drawn to  FIG. 3 , which provides a schematic view of a circuit  300  corresponding to a particular implementation of the circuit  200  of  FIG. 2 . While referring to  FIG. 3 , simultaneous reference will be made to  FIG. 2  and  FIG. 1 . 
         [0026]    As shown, a signal source  310  includes a frequency synthesizer  315  (e.g., a direct digital synthesis frequency synthesizer) and a signal source  320  includes a digital-to-analog converter (“DAC”)  325 . A comparator  340  includes a common vacuum environment  345  and an amplifier  349  (e.g., a precision ultra-low-drift operational amplifier that functions as an error amplifier). In this embodiment, the common vacuum environment  345  is configured in the same manner in which the common vacuum environment  145  is configured. Thus, the functions of the common vacuum environment  145  are applicable to the common vacuum environment  345 . 
         [0027]    According to  FIG. 3 , a servo loop is formed by applying a signal (e.g., a direct current (“DC”) or an alternating current (“AC”) signal from the DAC  325 ) to the lead  341   a  of the common vacuum environment  345 , and another signal (e.g., a DC or an AC signal) to the lead  342   a  of the common vacuum environment  345 . After the leads  341   a  and  342   a  receive their respective signals, the leads  343   a  and  344   a  of the common vacuum environment  345  each output a signal to the amplifier  349 . In this case, the two output signals released by the leads  343   a  and  344   a  are each based on a different one of the signals received by the leads  341   a  and  342   a.  The amplifier  349  compares the two output signals received from the leads  343   a  and  344   a,  and releases its own output signal to amplifier  330 . In accordance with one aspect of the invention, output signal is then operated upon in the circuit  300  to compensate for drift of offset and gain that exists in one or more of the components in the circuit  300 . 
         [0028]    For example, in one embodiment the output of the amplifier  349  may adjust the gain of an amplifier  330  (e.g., a variable gain amplifier) until the two output signals released by the leads  343   a  and  344   a  are equal/within a specified difference or until the servo loop is balanced. At this point, the true root-mean-square (“RMS”) value of the DC/AC signal applied to the lead  341   a  of the common vacuum environment  345  is equal to or within a specified difference of the DC/AC signal applied to the lead  342   a  of the common vacuum environment  345 . 
         [0029]    In another example, the output of the amplifier  349  may be used to compensate for minor drift in the thermocouple  343  of the common vacuum environment  345 . In yet another example, the output of the amplifier  349  may be used to compensate for drift created by connections in the circuit  300 , including possible thermal EMF created by solder joints. These examples are included only to illustrate some of the potential components in the circuit  300  that may cause drift. Moreover, these examples are not intended to limit the scope of the present invention. 
         [0030]    In one embodiment, the frequency synthesizer  315  comprises a direct digital synthesis (“DDS”) frequency synthesizer from which the frequency of an output of the circuit  300  is derived. The true RMS amplitude of the output of the circuit  300  is programmed by a direct current output of precision signals from the DAC  325 . These required signals could be applied and measured by means other than the DDS frequency synthesizer  315  and the DAC  325  as discussed here; however, their use enables a micro-processor interface to allow for some automation of operation. 
         [0031]    Another important consideration and feature of the present invention is a means to compensate for minor-order drifts with time and various environmental changes such as temperature. Regarding the drift compensation feature, attention is now drawn to  FIG. 4 , which depicts a block diagram of an exemplary drift compensation circuit  400 . 
         [0032]    As shown,  FIG. 4  includes a signal source  420 , a comparator  440 , an amplifier  450  and a measurement device  460 . The signal source  420  outputs a signal (e.g., a DC or an AC signal) that is received by the comparator  440  and the amplifier  450 . The signal received by the amplifier  450  is amplified or attenuated and then outputted to the comparator  440 . 
         [0033]    The comparator  440  receives two signals including a first signal directly from the signal source  420  and a second signal from the amplifier  450 . The comparator  440  compares the first and second signals and outputs a signal based on the comparison, which is received by the measuring device  460 . 
         [0034]    Upon receiving the signal outputted by the comparator  440 , the measuring device  460  determines whether minor-order drift(s) exist with respect to the amplifier  450  and/or other devices in the circuit  400  (if applicable). If the measuring device  460  determines that drift exists, the signal source  420  is notified and the signal outputted by the signal source  420  is adjusted to compensate for drift. 
         [0035]    Attention is now drawn to  FIG. 5 , which provides a schematic view of a circuit  500  corresponding to a particular implementation of the circuit  400  of  FIG. 4 . While referring to  FIG. 5 , simultaneous reference will be made to  FIG. 4 ,  FIG. 3  and  FIG. 1 . 
         [0036]    As shown, a signal source  520  includes a digital-to-analog converter (“DAC”)  525 , a comparator  540  includes a common vacuum environment  545  and an amplifier  549 , and a measuring device  560  includes an analog-to-digital converter (“ADC”)  565  that is configured to maintain critical circuit functionality. Both the common vacuum environment  545  and the amplifier  549  are similar in structure to the common vacuum environment  345  and the amplifier  349 , respectively, the descriptions of which are applied to this discussion of  FIG. 5 . 
         [0037]    Except as otherwise indicated below, the circuit shown in  FIG. 5  functions identically to the circuit described above with respect to  FIG. 4 . As shown in  FIG. 5 , the DAC  525  produces a signal (e.g., a DC or an AC signal) that is received directly by the lead  541   a  of the common vacuum environment  545  and indirectly, via an amplifier  550 , by the lead  542   a  of the common vacuum environment  545 . After the leads  541   a  and  542   a  receive their respective signals, the leads  543   a  and  544   a  of the common vacuum environment  545  each output a signal to the amplifier  549 . In this case, the two output signals released by the leads  543   a  and  544   a  are each based on a different one of the signals received by the leads  541   a  and  542   a.  The amplifier  549  compares the two output signals received from the leads  543   a  and  544   a,  and releases its own output signal that is then operated upon in the circuit  500  to compensate for any drift of offset and gain that exists in any of the components of circuit  500 . 
         [0038]    Since the signal output from the DAC  525  is essentially applied to both sides of the common vacuum environment  545  equally, the output signal of the amplifier  549  should indicate no difference in voltage between the heater-thermocouple pair  541 / 543  and  542 / 544  of the common vacuum environment  545 . 
         [0039]    If the output of the amplifier  549  indicates a difference in voltage between the heater-thermocouple pair  541 / 543  and  542 / 544  of the common vacuum environment  545 , then the ADC  565  will receive this information and adjust the DAC  525  accordingly to balance the two sides of the common vacuum environment  545 . 
         [0040]    Attention is now drawn to  FIG. 6 , which is a block diagram of a circuit  600  in accordance with an exemplary embodiment of the present invention that combines the functionalities and components described with respect to  FIGS. 1-5 . As shown, the circuit  600  includes signal sources  610 ,  620  and  670 , amplifiers  630  and  650 , a comparator  640 , a measuring device  660  and a switch  680 . The switch  680  can be positioned at position A to effect one feature of the present invention and at position B to effect another feature of the present invention. 
         [0041]    One feature of the circuitry shown in  FIG. 6  is to provide a precision output of the circuit  600 , programmable in both frequency and amplitude. In this case the switch  680  is positioned at position A. The frequency of the output of the circuit  600  is derived from the signal source  610  (e.g., a direct digital synthesis (“DDS”) frequency synthesizer  615 ). The true root-mean-square (“RMS”) amplitude of the output of the circuit  600  is programmed by the signal source  620  (e.g., a digital-to-analog converter (“DAC”)  625  and a Vernier DAC  629 ). These signals could be applied by means other than the DDS frequency synthesizer  615 , the DAC  625  and the Vernier DAC  629  as discussed here; however, their use enables a micro-processor interface to allow for some automation of operation. 
         [0042]    One focal point of the circuit  600  is a common vacuum environment  645  configured similarly to the common vacuum environment  145  of  FIG. 1 , the description of which is applied to this discussion of  FIG. 6 . The common vacuum environment  645  is connected to an amplifier  649  (e.g., a precision ultra-low-drift operational amplifier that functions as an error amplifier). 
         [0043]    A servo loop is formed by applying a first signal (e.g., a precision DC or AC signal) from the signal source  620  to the lead  641   a  of the common vacuum environment  645 , and a second signal (e.g., a DC or AC signal) to the lead  642   a  of the common vacuum environment  645 . After the leads  641   a  and  642   a  receive their respective signals, the leads  643   a  and  644   a  of the common vacuum environment  645  each output a signal to the amplifier  649 . In this case, the two output signals released by the leads  643   a  and  644   a  are each based on a different one of the signals received by the leads  641   a  and  642   a.  The amplifier  649  compares the two output signals received from the leads  643   a  and  644   a,  and releases its own output signal based on differences in voltage between the heater-thermocouple pair  641 / 643  and  642 / 644  of the common vacuum environment  645 . The output signal released by the amplifier  649  is then operated upon in circuit  600  to compensate for drift of offset and gain that exists in one or more of the components in circuit  600 . 
         [0044]    For example, the output of the amplifier  649  is operated upon to adjust the gain of the amplifier  630  (e.g., a variable gain amplifier) until the voltages of the heater-thermocouples  641 / 643  and  642 / 644  are equal and the servo loop is balanced. At this point, the true RMS value of the second signal applied to the lead  642   a  of the common vacuum environment  645  is equal to the first signal applied to the lead  641   a  of the common vacuum environment  645 . Additionally, the true RMS amplitude of the output of circuit  600  is related to the value of the second signal by the gain or attenuation of the amplifier  650 . 
         [0045]    As described before with respect to  FIG. 1 , an important consideration and feature of the common vacuum environment  645  used in several embodiments of the present invention is that the gain of each heater-thermocouple  641 / 643  and  642 / 644  remains relatively constant with respect to each other on a short term basis. If the heater-thermocouples  641 / 643  and  642 / 644  were to be housed in separate glass envelopes, their gains would differ significantly as a function of temperature. Thus, in order to ensure that each heater-thermocouple  641 / 643  and  642 / 644  operates in an identical environment, embodiments of the invention place both heater-thermocouple units in the same evacuated glass envelope. 
         [0046]    Another feature of this invention is a means to compensate for inevitable minor-order drifts with time of offset and gain in the common vacuum environment  645  and/or the sensitive servo loop circuitry (e.g., the amplifier  650  and/or one or more solder joints). This drift compensation is necessary in order to achieve high accuracy and long-term stability, and is accomplished by utilizing the measuring device  660  (e.g., an analog-to-digital converter (“ADC”)  665 ), the signal source  670  (e.g., an offset DAC  675 ), and the signal source  620 . 
         [0047]    The offset and gain stabilization operation is initiated by moving the switch  680  to position B. This serves to apply the current-summed output signal from the DAC  625  and the Vernier DAC  629  to both sides of the common vacuum environment  645 . Serving only as an example, the amplifier  650  is included in the circuitry  600  in order to compensate for any drifts associated with the amplifier  650 . One of skill in the art will recognize other components that may be included in place of or in addition to the amplifier  650 . 
         [0048]    Initially, both the DAC  625  and the Vernier DAC  629  are programmed to zero. Under this condition, the output of the offset DAC  675  is programmed to a level such that the ADC  665 , which is connected to the output of the amplifier  649 , measures a known reference voltage. One of ordinary skill in the art will appreciate that the exact reference voltage value is not important and may depend on the particular output stage design of the amplifier  649 . 
         [0049]    Next, while still applying the offset DAC  675  value, the DAC  625  output is adjusted to provide the full scale deviation of the common vacuum environment  645 . The ADC  665  will measure the output signal of the amplifier  649 . If the ADC  665  does not measure the same reference voltage as described above, the Vernier DAC  629  is adjusted until the ADC  665  measures the same reference voltage as described above. 
         [0050]    As a consequence of these measurements and adjustments, the offset and gain characteristics of circuit  600  are restored to the same reference value within the capability of the ADC  665 . When the switch  680  is restored to position A, the offset DAC  675  and the Vernier DAC  629  remain set to the values established during the operation phase of position B. The flipping of the switch  680  from position A to position B is performed after temperature stability is achieved in position A, and thereafter incrementally (e.g., on a time basis of seconds, hours, days, weeks, months, or years) or upon the happening of some event. 
         [0051]    Alternative embodiments of the present invention may include different configurations of circuit design. In one such embodiment, as depicted in  FIG. 7 , a circuit  700  can be realized by reconfiguring the circuit design of  FIG. 6 . The components shown for  FIG. 7  are for illustrative purposes only. One of skill in the art will appreciate alternative embodiments of  FIG. 7  comprising fewer or more components that shown in  FIG. 7 . 
         [0052]    As shown, the circuit  700  comprises signal sources  715 ,  725 ,  729  and  775 , amplifiers  730  and  749 , a common vacuum environment  745 , a measurement device  765  and switches  780 . The switches  780  are configured to switch from position A to position B and from position B to position A. 
         [0053]    When the switches  780  are in position B, the signal source  725  (e.g., a digital-to-analog converter) and the signal source  729  (e.g., a Vernier digital-to-analog converter) are set to zero, while the signal source  775  (e.g., a digital-to-analog converter) is adjusted to produce some arbitrary reference value (e.g., 200 mV) which is read by the measurement device  765  (e.g., an analog-to-digital converter). The exact value produced by the signal source  775  and measured by  765  will become the reference for all future adjustments; however, the actual value serving as the reference is unimportant so long as it is within the range configured for the amplifier  749  and it remains unchanged. 
         [0054]    Once the reference value of the circuit  700  is set, the signal source  725  releases a signal representing a full-scale deviation of the common vacuum environment  745  that is sent to two heaters  741  and  742  (e.g., similar to the heaters  141  and  142  of  FIG. 1 ) of the common vacuum environment  745 . Before reaching the heater  741 , the signal passes through the amplifier  730 . The signals received by the heater  741  and the heater  742  are each thermally converted. The thermally converted signals from heaters  741  and  742  are received by thermocouples  743  and  744 , respectively (e.g., similar to the thermocouples  143  and  144  of  FIG. 1 ). A comparison of the resulting thermocouple values is performed by the amplifier  749 , which outputs a signal based on the comparison. The signal outputted by the amplifier  749  is then received by the measuring device  765 . Since the signal from the signal source  725  is applied to both sides of the common vacuum environment  745 , the output as represented by the amplifier  749  should be the same as the reference value. If the measurement taken by the measuring device  765  does not measure the reference value, then the signal source  729 , which operates on the amplification of amplifier  730 , is adjusted until the measurement device  765  measures the reference value (which is still applied by the operation of signal source  775 ). This adjustment compensates for drift in the circuit  700 . 
         [0055]    When the switches  780  are in position A, the signal source  729  (which adjusts amplification of the amplifier  730 ) and the signal source  775  are maintained consistent with the adjustment made in the manner described above with respect to position B. The signal source  715  outputs a signal that is received by the amplifier  730  and a resulting amplified signal is sent from the amplifier  730  to the heater  741 . A thermal conversion of this signal is received by the thermocouple  743 , which is electronically connected to the amplifier  749 . A feedback signal generated by the amplifier  749  is received by the heater  742 , and a thermal conversion of this feedback signal is thermodynamically communicated to the thermocouple  744 , which is electronically connected to the amplifier  749 . 
         [0056]    At this point, the amplifier  749  compares the values of the thermocouples  743  and  744  and outputs a signal indicative of the result of the comparison. When the servo loop created by the feedback signal is balanced, the output of the amplifier  749  will be equivalent to the root-mean-square value of the signal outputted by the signal source  715 . 
         [0057]    In conclusion, the present invention provides, among other things, a system and method for controlling the long-term stability and accuracy of circuitry that can be used to control an output waveform or used as a measurement device. Those skilled in the art can readily recognize that numerous variations and substitutions may be made in the invention, its use and its configuration to achieve substantially the same results as achieved by the embodiments described herein. Accordingly, there is no intention to limit the invention to the disclosed exemplary forms. Many variations, modifications and alternative constructions fall within the scope and spirit of the disclosed invention as expressed in the claims.