Abstract:
A portable calibration unit for calibrating test equipment is disclosed that may incorporate a communication interface for connecting to a computer embedded within the test equipment, a variable signal source for producing a test signal, a processor in communication with the computer for controlling the variable signal source, and a test interface for communicating the test signal to the test equipment.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates, in general, to testing equipment, and more specifically to a portable calibration unit for test equipment.  
       BACKGROUND OF THE INVENTION  
       [0002]     In various manufacturing processes, such as the manufacture of radio frequency (RF) equipment, cell phones, and the like, testing equipment is typically included at various stages of the process to test the operation of each item produced. This testing equipment may either make up a part of the production line or may be a portable or transportable system maintained in proximity to the production line. While the use of testing equipment helps to ensure that the manufactured items operate correctly within a given set of parameters, the testing performed would be of little use if the testing equipment was not, itself, reliably accurate. Therefore, additional verification equipment is typically used to test the main-line testing equipment.  
         [0003]     Test systems, like other electronic equipment, are susceptible to anomalies such as electronic drift, wear in cables or connectors, and the like, as time passes. Therefore, such equipment is routinely checked to verify its accuracy. By periodically checking the test equipment, electronic and physical faults, such as worn cables, connectors, or the like, may be fixed or adjusted. Furthermore, because environmental conditions play an important role in the testing of the manufactured items, the main test equipment is typically checked in place. Currently, verification equipment is routinely placed on a mobile test cart that may be moved around the factory floor to check the various test equipment. The group of equipment on the cart is sometimes referred to as a calibration cart. A calibration cart generally includes a source and power meter with a system controller, various couplers to connect to the different inputs or outputs of the test set, and at least one computers to run the testing and calibration applications for the calibration cart hardware. Therefore, a verification application on a calibration cart computer may cause a source signal to be transmitted to the input of the test set or test equipment to check various elements, such as the insertion loss of the cables, the test set set-up, all of the switches that would be found between the test set, the manufactured items, and/or other such elements. On a typical production line, there are many different cables, switch boxes, adapters, and the like that make up a part of the overall testing system. The calibration cart is generally moved down the line to test each of these components. Power is typically supplied to a cart through an alternating current (AC) power source. It may also include an uninterruptible power supply (UPS) to maintain power in the equipment as it is being moved from station to station and AC outlet to AC outlet.  
         [0004]     While providing a means at verifying the accuracy and integrity of testing equipment, one of the main problems with the calibration cart is the inconvenience of moving the cart around and plugging it in repeatedly. Moreover, current calibration carts are generally custom built to a particular production line, running a particular testing format. It then becomes impracticable or expensive to create another calibration cart to verify or calibrate test equipment running the different format. For applications in the cellular communications industry, there are several different formats, sometimes even within the same phone. Further, as product prices fall and the margins of profit narrow, the cart method of verifying test sets and test equipment provides a relatively expensive solution to a systematic part of the manufacturing process.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     Representative embodiments of the present test equipment calibration system are directed to a portable calibration unit for calibrating test equipment that may incorporate a communication interface for connecting to a computer embedded within the test equipment, a variable signal source for producing a test signal, a processor in communication with the computer for controlling the variable signal source, and a test interface for communicating the test signal to the test equipment.  
         [0006]     Additional representative embodiments of the present test equipment calibration system are directed to a method for portably calibrating a test system comprising establishing a communication link between a calibration pod and a personal computer (PC) embedded within the test system, generating a test signal within the calibration pod responsive to a digital signal received from the PC, and transmitting the test signal to a test subject of the test system.  
         [0007]     Further representative embodiments of the present test equipment calibration system are directed to a system for calibrating test equipment comprising a calibration unit having an interface for connecting to a personal computer (PC) embedded in the test equipment, a processor within the calibration unit, the processor configured to receive digital control signals from the PC, a signal source for generating a test signal responsive to the digital control signals, and a test connection for connecting the calibration unit to the test equipment, wherein the test signal is transmitted to the test equipment using the test connection.  
         [0008]     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized that such equivalent constructions do not depart from the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:  
         [0010]      FIG. 1  is a block diagram illustrating a calibration pod configured according to one embodiment of the system described herein connected to a test set;  
         [0011]      FIG. 2  is a block diagram illustrating another embodiment of a calibration pod configured according to the teachings herein;  
         [0012]      FIG. 3  is an additional embodiment of a calibration pod configured according to the teachings herein; and  
         [0013]      FIG. 4  is a block diagram illustrating an additional embodiment of a calibration pod configured for multi-level verification. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]      FIG. 1  is a block diagram illustrating calibration pod  100  configured according to one embodiment of the system described herein connected to test set  101 . Test set  101  is configured with embedded PC  102  for running applications used in testing the integrity and accuracy of the manufactured items. Calibration pod  100  is implemented in a small or handheld unit complete with a standard set of connectors that may be used to connect to different parts of test set  101  or to the manufactured item. Calibration pod  100  may also include system connectors, such as USB connection  103 , to facilitate connection with embedded PC  102 . Because standard USB connections are capable of supplying up to 5 Volts at 100 milliamps from the host device, calibration pod  100  may be powered completely by test set  101  through USB connection  103 , thus, in some embodiments, relieving the need for an external AC power source.  
         [0015]     In operation, after successful communication on the initiation of USB connection  103 , embedded PC  102  recognizes calibration pod  100  and runs a verification application native within a memory of embedded PC  102  that controls the verification processes of calibration pod  100 . The verification application or instruction logic may be stored in firmware, random access memory (RAM), flash memory, disk drives, or other such non-volatile memory. Because the verification logic is maintained on PC  102  within test set  101 , calibration pod does not need to have a high performance processor or computer, as is found in the calibration carts, and, may then be smaller in size. Moreover, different formats or systems may be tested using calibration pod  100  simply by running a different verification application.  
         [0016]     PC  102  executes the verification application upon recognition of calibration pod  100 , or upon a user-selection in response to a prompt displayed after the connection of calibration pod  100 . The verification application controls the specific test signals and measurements performed by calibration pod  100 . Test signals issued over link  104  into RF input  105  may then test many different aspects and features of test set  101 . The output levels or verification results may then be read for display to the user technician.  
         [0017]      FIG. 2  is a block diagram illustrating another embodiment of calibration pod  100 . Calibration pod  100  includes processor  200 , which not only manages USB connection  103 , but also assists in controlling the verification and calibration process. The embodiment of calibration pod  100  shown in  FIG. 1  used the measurement facilities of test set  101  to sense and detect the levels of signals delivered by calibration pod  100 . The embodiment shown in  FIG. 2  includes digital to analog converter (DAC)  201  connected between processor  200  and voltage controlled oscillator (VCO)  202 . Normal verification and calibration process may check the test subjects over various frequencies. In order to implement such multi-frequency testing, the verification application being run from PC  102  may signal VCO  202  through processor  200  and, thereafter, through DAC  201 , to vary the signal produced at VCO  202 . In this manner, the verification application may transmit multi-frequency test signals to test set  101 . Various types of VCOs may be used to implement VCO  202 . One example may be an octave VCO, which tunes over octaves and is typically useful in suppressing certain types of noise.  
         [0018]     In operation, as calibration pod  100  is connected to embedded PC  102  through USB connection  103 , the verification application run by PC  102  may set the desired test frequency to be generated from calibration pod  100 . For example, some selected embodiments designed to test Personal Communication Service (PCS) radios in the United States may implement VCO  202  to produce test signals in the range of 850-1900 MHz, which covers the cellular communication bands in the United States. Signals from PC  102  direct what frequency at which to set VCO  202  according to what cellular signal service is currently being tested. Filter bank  203  is also included in calibration pod  100  for conditioning the signal from VCO  202 . In selected embodiments, filter bank  203  may be a low pass filter to attenuate the harmonics that interfere with measurement of the signal power of test set  101 . From filter bank  203 , the test signal enters power amp  205  whose output is sampled in automatic level control (ALC)  206  loop. ALC  206  operates to condition the output from power amp  205 . Therefore, the signal output from power amp  205  will generally be produced at a single, constant level, such as 0 dBm, 10 dBm, or the like. R out  is the output impedance connecting to the test signal communication line. The value of R out  is usually selected to match the impedance of the system for purposes of signal transmission. Therefore, RF input  105  will see a single, constant level test signal transmitted from calibration pod  100 .  
         [0019]      FIG. 3  is an additional embodiment of calibration pod  100  configured according to the teachings herein. Instead of verifying test set  101  using a known or presumed single signal level, the embodiment of calibration pod  100  depicted in  FIG. 3  physically measures the signal level exiting ALC  206  to be used by the verification application. In order for test set  101  to effectively process the test/verification data, analog-to-digital converter  300  (ADC) converts the analog output signals from ALC  206  into digital data and transmits that information to processor  200 . Processor  200  may then communicate the data back to embedded PC  102  for use in the executing verification software. The verification application receives the measurement of the actual output level being transmitted from power amp  205  and may use that information to compare with the signal level measurements obtained from test set  101 .  
         [0020]     The embodiment of calibration pod  100  illustrated in  FIG. 3  also includes power connection  301  for providing power in excess of what can be supplied by USB connection  103 . Some applications may need signal levels that exceed the levels achieved with power supplied directly from USB connection  103 . In such implementations, power connection  301  may be included to reach the desired output levels.  
         [0021]     While the embodiment of calibration pod  100  depicted in  FIG. 3  allows for the actual measurement of signal level to be performed on ALC  206  output, the embodiment of pod  100  shown in  FIG. 4  includes elements allowing embedded PC  102  to control or vary the signal level set by ALC  206 .  FIG. 4  is a block diagram illustrating an additional embodiment of calibration pod  100  configured for multi-level verification. To accomplish this multi-level test signal generation, DAC  402  is added to the communication line of ADC  401 . Therefore, ADC  401  reads the actual output level of ALC  206  and communicates that value back to embedded PC  102  through processor  200  and DAC  402  transmits control signals to ALC  206  to vary the desired output signal level for power amp  205 . The verification logic running on embedded PC  102  may send signals to processor  200  detailing the signal level desired for testing. Processor  200  then transmits those control signals to DAC  402 , which converts the signals to analog control signals for changing the output of ALC  206 . Therefore, calibration pod  100  of  FIG. 3  cannot only read the actual output signal level of power amp  205 , but may also control what level to set.  
         [0022]     The embodiment of calibration pod  100  shown in  FIG. 4  may also be configured to operate with embodiments of test set  101  that are extremely accurate and sensitive. Verifying such accurate and sensitive equipment generally requires using a more accurate and sensitive test signals. The range of signal frequencies that may be produced is generally limited to the VCO used. A VCO that can produce a wide range of frequencies typically has a larger gap between frequency steps. In order to produce a finer step size with an ordinary VCO the range of available frequencies generally decreases. Therefore, to obtain a smaller resolution of frequencies using only a VCO, a trade-off in overall signal range is typically accepted.  
         [0023]     A means for producing a wide range of frequencies having a finer resolution in step size is to implement a fractional-n phase locked loop (PLL). Calibration pod  100 , as shown in  FIG. 4 , incorporates fractional-n PLL  400  to create a finer resolution step size of the reference signals generated by VCO  202 . A test reference generated at test set  101  is communicated to fractional-n PLL  400  to establish the resolution size of the test signal generated by VCO  202 . This test reference enters calibration pod  100  at RefIN  403 . Using the test reference from test set  101  and the output signal of VCO  202 , the resolution of the output signal may be selected at a much finer step size than that produced by VCO  202  alone. The finer step size allows calibration pod  100  to transmit test signals at a wider variety of frequencies over a larger frequency band. Therefore, the more accurate and sensitive test equipment may be verified over a wide and varied band of frequencies.  
         [0024]     An additional consideration that is generally made in designing calibration equipment is the temperature stability of the internal components. The components of the ALC, in addition to any possible diode detector positioned to detect the expected signal level output of the calibration pod may be subject to temperature drift. Temperature drift is the variation in signal produced across different temperatures of the equipment. When moving a calibration pod from test site to test site, the components may vary in temperature as the power is applied and then stopped repeatedly. This variation in temperature may prevent the generated stimulus signal from remaining level at the different test points. Calibration carts would typically need to be re-calibrated when the temperature varied by a certain degree. One method to overcome the temperature drift is to include an ovenizing circuit to quickly heat the temperature sensitive equipment to a constant, optimal temperature.  
         [0025]      FIG. 5  is a block diagram illustrating an additional embodiment of calibration pod  100  configured for multi-level verification. As indicated in  FIG. 5 , power amplifier  205  and diode detector  207  are placed within the coverage of ovenizer  50 . Ovenizer  50  may comprise a simple resistor network, or some other type of heating element that may quickly heat the components of diode detector  207  and power amplifier  205  to a stable, optimum temperature. Therefore, when a user plugs calibration pod  100  into a power source, ovenizer  50  quickly heats diode detector  207  and power amplifier  205  to a stable, optimum temperature. Once the heating has occurred, which may be a very short amount of time, the user is prompted that the calibration pod is ready for use.  
         [0026]     In various additional embodiments of calibration pod  100 , it is desirable to provide ovenizer  50  in such a manner to obviate the need to re-calibrate across the temperature flux of the system. In very accurate and sensitive test systems it may be desirable for a calibration pod to have its full accuracy over 25 degrees Celcius (+/−15 degrees) without requiring a re-calculation of calibration pod  100  over this design temperature range. For this reason embodiments of calibration pod  100  may ovenize diode detector  207  and ALC power amplifier  205  which may keep calibration pod  100  small and compact.  
         [0027]     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.