Abstract:
A signal conditioning integrated circuit includes both signal conditioning circuitry and memory devoted to storing end-user downloadable coefficients. In a preferred embodiment, the integrated circuit is an Application Specific Integrated Circuit (ASIC), and the end-user downloadable coefficients, based upon a mathematical equation pre-selected by the end-user, are pre-stored in the ASIC when a sensor device with which the ASIC is associated is calibrated. This results in a customized and more cost-effective and space-efficient signal-conditioning apparatus with improved functionality over that available in the prior art.

Description:
FIELD OF THE INVENTION 
     This invention relates to the conditioning of signals sensed by sensor transducers. 
     BACKGROUND OF THE INVENTION 
     A transducer is a device that converts one type of energy into another type of energy for the purpose of measurement or information transfer. A sensor transducer is a type of transducer that detects (senses) a signal or physical condition and converts it to a signal that can be read and analyzed by humans. Examples of devices that use sensor transducers include mass airflow sensors, speed sensors, position sensors, pressure sensors, relative humidity sensors, and the like. 
     As is well known, the output of a sensor transducer, referred to herein as a “raw signal”, must be conditioned so that it can be properly used by an end-user. Signal conditioning circuits and conditioning techniques (also referred to as “signal compensation” or “signal correction”) condition raw signals from sensor transducers, regardless of the quantity being measured by the sensor transducer or the sensor transducer technologies. 
     Some sensor transducers have very linear and stable outputs and require minimal conditioning; other sensor transducer technologies produce extremely non-linear signals and require a significant amount of conditioning to meet required linear outputs. Ambient temperature and the sensitivities of the various sensing technologies can also affect the linearity and stability of the signal output from a sensor transducer, further adding to the need to condition the output signal. 
     Application Specific Integrated Circuits (ASICs) have been developed for conditioning sensor transducer signals, and these ASICs offer a wide variety of programming options that can be specifically tailored to match the characteristics of the particular sensor technology. Because there are so many different types of sensors on the market (pressure, airflow, speed, position, etc.), it is practically impossible to design an affordable ASIC capable of conditioning the raw signals output from every type of transducer. However, in most cases raw signals need to be conditioned for similar characteristics (sensitivity, offset, temperature induced sensitivity changes, temperature induced offset changes and non-linear characteristics) and thus generic conditioning circuits with the ability to “coarsely” condition raw signals for these basic characteristics have been developed. Coarse conditioning as used herein refers to conditioning of a signal using lower order polynomial expressions, e.g., 2 nd  order polynomial expressions or lower. Typical conditions for which coarse conditioning would be appropriate include compensating a signal for sensitivity changes due to temperature or signal offset changes due to temperature. 
     Currently, sensor manufacturers are using two methods to condition a raw signal output from a sensor transducer and deliver it to the user, each of which is advantageous in its own way. In a first method, a signal conditioning ASIC includes a conditioning circuit capable of coarsely conditioning the raw signal and delivers this coarsely-conditioned signal to the end-user. Since the basic level of conditioning is provided by the ASIC, the end-user need not provide or use its own processors to perform conditioning, thereby freeing them up for other tasks. A drawback, as described above, is that the robustness of the conditioning is limited in favor of having a signal conditioning chip that can be used in a wide variety of applications. 
     A second method is to provide the end-user with downloadable compensation coefficients that are applied to conditioning equations processed by the processor(s) of the end-user device receiving a raw signal from a sensor. In practice, memory such as a TEDS (Transducer Electronic Data Sheet) IC stores downloadable coefficients that can be used in applications such as signal conditioning applications. A sensor transducer outputs a raw signal to the end-user device, and the optimal coefficients that have been downloaded from the memory are used by a processor in the end-user&#39;s system to apply to equations that perform the desired conditioning. Using downloadable coefficients from a memory location gives an end-user the flexibility to, when needed, use higher order (e.g., 3 rd  order polynomial expressions or greater) exponential functions to condition the raw transducer signals, instead of having to use the more generic conditioning coefficients provided by the signal-conditioning ASIC described above. However, since the end-user performs the conditioning process on the raw signals coming directly from the sensor transducer, the end-user must tie up its processors for conditioning purposes. 
     It would be desirable to have an integrated circuit customized to the needs of a particular end-user and providing both a coarsely-conditioned signal to the end-user and the downloadable coefficients needed to provide higher level conditioning when needed. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a signal conditioning integrated circuit includes both signal conditioning circuitry and memory devoted to storing end-user downloadable coefficients. In a preferred embodiment, the integrated circuit is an Application Specific Integrated Circuit (ASIC), and the end-user downloadable coefficients, based upon a mathematical equation pre-selected by the end-user, are pre-stored in the ASIC when the sensor device is calibrated. This results in a customized and more cost-effective and space-efficient signal-conditioning apparatus with improved functionality over that available in the prior art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating the basic structure and concept of an apparatus according to the present invention; 
         FIG. 2  is a flowchart illustrating steps performed in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a block diagram illustrating the basic structure and concept of a preferred embodiment of the present invention. Referring to  FIG. 1 , a sensor  100  includes a sensor transducer  102  outputting a raw signal to an input  112  of a signal conditioner  108  of an ASIC  104 . Sensor  100  can be any kind of sensor, for example, a mass airflow sensor, a speed sensor, a position sensor, a pressure sensor, a relative humidity sensor, etc. The raw signal corresponds to a parameter sensed by sensor transducer  102 . Signal conditioner  108  conditions the raw signal from sensor transducer  102  in a well-known manner, using lower-order polynomial expressions (e.g., 2 nd  order or lower) to produce a coarsely-conditioned signal which is output, in this example, to end-user device  110  via an output  116 . 
     End-user device  110  can comprise, for example, a microprocessor used by the end-user to analyze, store, and otherwise use the data coming from sensor  102 . The microprocessor may be dedicated for that purpose; more typically the microprocessor will be part of a larger processing device that uses the analyzed data for some other purpose, e.g., an air-flow monitor used for monitoring the breathing of a hospital patient. 
     ASIC  104  is situated between sensor transducer  102  and end-user device  110 . ASIC  104  is equipped with memory  106 . This memory  106  stores specific coefficients downloadable to the end-user device  110  by the end-user via an output  114  to perform particular tasks. For example, the end-user may have use for the coarsely conditioned signal from signal conditioner  108  for a certain application, but also have a need for a more linearized signal resulting from the further conditioning of the coarsely conditioned signal using a predetermined equation and certain sensor-specific sinusoidal Fourier coefficients. In accordance with the present invention, when the sensor  100  is provided to the end-user, memory  106  has these Fourier coefficients specific to needs of that particular end-user stored and available for the end-user to download. 
     Thus, the end-user can take sensor  100 , connect it to their end-user device  110 , and download the downloadable coefficients from memory  106 , before receiving sensed signals from sensor  100 . This configures the end-user device  110  to both receive the coarsely compensated signals from signal conditioner  108 , and gives them the ability to apply the predetermined equations downloaded from memory  106  to the coarsely compensated signal and compensate it even further to achieve a more accurate, highly compensated signal. This second level of compensation, performed using the downloadable coefficients, is referred to herein as “fine conditioning” and means conditioning the signal using polynomial expressions of an order higher than those used for coarse conditioning, e.g., 3 rd  order polynomial expressions or greater. 
     In the drawing of  FIG. 1 , the sensor transducer  102  and ASIC  104  are illustrated as being integrated into sensor  100 ; however, it is understood that sensor  102  and ASIC  104  can be separate (non-integrated) components and such a non-integrated configuration falls within the scope of the invention claimed herein. Further, in the preferred embodiment the memory  106  and signal conditioner  108  are configured in an ASIC; however, it is understood that the memory  106  and signal conditioner  108  can also be configured in a general purpose integrated circuit and such a configuration falls within the scope of the invention claimed herein. 
     Although memory  106  could be loaded with a set of generic coefficients that could be usable by any end-user, in the preferred embodiment, memory  106  is preconfigured, prior to delivery for use by the end-user, with only the specific coefficients needed for application to the conditioning equation (s) being used by the end-user. In a preferred embodiment, the memory comprises an Electrically Erasable Programmable Read Only Memory (EEPROM). The process of loading a memory with coefficients is a known process and is not described further herein. Further, while in the examples above the “lower order” polynomial expressions are described as being 2 nd  order or lower and the higher level of conditioning is described as being performed using 3 rd  order or higher polynomial expressions, these values are given for the purpose of example only. Of relevance to the present invention is that a first level of conditioning is performed by the signal conditioning circuitry on board the IC, and a second level of conditioning is performed by the end-user device using the downloadable coefficients stored in the memory of the IC. 
       FIG. 2  is a flowchart illustrating steps performed in accordance with the present invention. At step  200 , the sensor manufacturer/supplier and the end-user agree upon one or more conditioning equations that will be used to finely condition the coarsely-conditioned signal received from sensor  100 . The equation will differ, for example, depending on the linearity or non-linearity of the raw signal output by the sensor. 
     At step  202 , the sensor is calibrated, and coefficients for the equation(s) being used by the end-user are downloaded to the ASIC memory. Preferably, the coefficients for the equation(s) requested by the end-user are installed at the factory at the same time that the sensor is tested during calibration. Alternatively, the coefficients could be stored during a post-manufacture process prior to delivery to the end-user. 
     At step  204 , the sensor  100  is connected to the end-user device. At step  206 , upon connection to the end-user device, the coefficients from the ASIC memory are downloaded to the end-user device so that they are available for use. If desired, this step can be deferred until the coefficients are actually needed. At step  208 , the end-user device receives coarsely-conditioned signals from signal conditioner  108  of sensor  100 . 
     At step  210 , a determination is made as to whether or not fine conditioning is desired. If fine conditioning is desired, the process proceeds to step  212 , where further conditioning is performed on the signals using the downloaded coefficients and the appropriate equation, and then the process proceeds to step  214 , where the fine-conditioned signal is used for its intended purpose. If at step  210  it is determined that fine conditioning is not desired, the process proceeds directly to step  214  and the coarsely-conditioned signal is used for its desired purpose. 
     By incorporating the ability to have downloadable coefficients pre-loaded into a sensor delivered to an end-user, the sensor manufacturer can deliver a highly accurate sensor that can still be used in numerous settings. This, in turn, keeps the overall sensor cost down which is a positive result for both the manufacturer and end-user. 
     The above-described steps can be implemented using standard well-known programming techniques. The novelty of the above-described embodiment lies not in the specific programming techniques but in the use of the steps described to achieve the described results. Software programming code which embodies the present invention is typically stored in permanent storage. In a client/server environment, such software programming code may be stored with storage associated with a server. The software programming code may be embodied on any of a variety of known media for use with a data processing system, such as a diskette, or hard drive, or CD ROM. The code may be distributed on such media, or may be distributed to users from the memory or storage of one computer system over a network of some type to other computer systems for use by users of such other systems. The techniques and methods for embodying software program code on physical media and/or distributing software code via networks are well known and will not be further discussed herein. 
     It will be understood that each element of the illustrations, and combinations of elements in the illustrations, can be implemented by general and/or special purpose hardware-based systems that perform the specified functions or steps, or by combinations of general and/or special-purpose hardware and computer instructions. 
     These program instructions may be provided to a processor to produce a machine, such that the instructions that execute on the processor create means for implementing the functions specified in the illustrations. The computer program instructions may be executed by a processor to cause a series of operational steps to be performed by the processor to produce a computer-implemented process such that the instructions that execute on the processor provide steps for implementing the functions specified in the illustrations. Accordingly, the figures support combinations of means for performing the specified functions, combinations of steps for performing the specified functions, and program instruction means for performing the specified functions. 
     While there has been described herein the principles of the invention, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation to the scope of the invention. Accordingly, it is intended by the appended claims, to cover all modifications of the invention which fall within the true spirit and scope of the invention.