Abstract:
An adaptive power control device and method are disclosed in which characteristics of a transfer function of a power control system are dynamically manipulated upon selective variation of a sampling rate of power control output values. Systematic monitoring of critical sampling rates allows for alternate assignment of part of a power control system workload during slower sampling frequencies. Upon determination of an operably insignificant variation of a power control system output value from a previous power control system output value, the sampling rate is decreased, enabling reallocation of a portion of the workkload of the digital power control device.

Description:
BACKGROUND OF THE INVENTION 
     Digital power controls typically use a constant sampling method, selecting a sampling rate for particular power control characteristics. Changing a power control characteristic generally requires modification of a transfer function of a control device, which in turn typically requires modification of a physical component of a related control system. 
     Adaptive analog power control systems have been developed such as SPECTRA 800 and 900 MHz power control. The need exists for an adaptive digital power control system that allows alteration of a digital power control without requiring simultaneous physical modification of the system. 
     SUMMARY OF THE INVENTION 
     The need for a digital power control device for altering the degree of dedication of a system to power control without requiring simultaneous physical modification of that system and other needs are substantially met by the present invention. 
     An adaptive power control device and method are provided for controlling, at least in part, a controlled device having a transfer function, by selectively utilizing a modified digital power control sampling rate to adjust the transfer function. 
     A control device is utilized for controlling, at least in part, a controlled device having a transfer function, wherein the control device controls the controlled device, at least in part, by sampling an output parameter of the controlled device at a sample rate to obtain at least three sample values: a selected sample value, a sample value previous thereto, and a further selected sample value. The control device utilizes the sample values of the output parameter to control the sample rate as a function of the output parameter sample values, and to automatically alter the transfer function as a function, at least in part, of the sample rate. 
     One embodiment utilizes a comparison of consecutive differences of the sampled output parameter to determine a modification of the sampling rate that will adjust the controlled device transfer function so as to obtain a desired output parameter. 
     Another embodiment utilizes a standard deviation algorithm to determine when a delay of sampling may be utilized, thereby optimizing the control function process and, at the same time, increasing the efficiency of the controlled device by allowing the controlled device to perform additional functions during the delay time. 
     A method for controlling, at least in part, a controlled device having a transfer function, by sampling an output parameter of the controlled device at a selected sample rate to obtain at least three sample values, and utilization of the sample values as set forth above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flow diagram setting forth a digital power control method utilizing a power difference detection technique in accordance with the present invention. 
     FIG. 2 is a flow diagram setting forth a digital power control method utilizing a standard deviation algorithm. 
     FIG. 3 is a block diagram of a microprocessor-based power control system for a power amplifier in accordance with this invention. 
     FIG. 4 is a block diagram of a closed loop feedback control system implemented in accordance with the present invention. 
     FIG. 5 is a diagram illustrating root loci of a second order control system with varying sampling times as utilized with the present invention. 
     FIG. 6 is a graph illustrating a sampling time switching for a unit step power response of a second order system with respect to time in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1, generally depicted by the numeral 100, sets forth a flow diagram of a digital power control method utilizing a power difference detection technique in accordance with the present invention. 
     In one embodiment, an initial output parameter (OP init) of a controlled device is sampled (102), followed by another sampling of the output parameter (OP) at a selected time (104). A typical initial output parameter value is zero. The output parameter is sampled (104) at least three times, obtaining at least three samples: a selected sample, a sample previous thereto, and a further selected sample. The sample previous thereto is that sample obtained immediately previous thereto and the further selected sample is that sample obtained immediately subsequently thereto. A typical output parameter sampled is an output power of the controlled device. A first difference between the selected sample of the output parameter and the sample previous thereto is determined (106), and a second difference between the selected sample (108) and the further selected sample is also determined (110). The first difference is compared with with the second difference (112, 120). 
     When the second difference, a current difference (DIFF cur), is greater than the first difference, a previous difference (DIFF prev), and the first difference is substantially equal to zero (114), a predetermined maximum sample rate allocated for control usage, f ns , is set (118). A typical predetermined maximum sample rate allocated for control usage is 2.5 KHz. 
     When the second difference, a current difference (DIFF cur), is greater than the first difference, a previous difference (DIFF prev), and the first difference is not substantially equal to zero (114), a maximum sample rate value is selected as the smallest of: a product of the utilized sample rate multiplied by two (f*2), and a predetermined maximum sample rate allocated for control usage (f ns ) (116). 
     When the second difference, a current difference (DIFF cur), is less than the first difference, a previous difference (DIFF prev) (120), a maximum sample rate is selected as the larger of: a quotient of the utilized sample rate divided by two (f/2), and a predetermined minimum sample rate allocated for control usage (f min ) (122). A typical predetermined minimum sample rate allocated for control usage is 50 Hz. 
     After utilizing the comparison of the first difference and the second difference to obtain a selected sample rate (116, 118, 122 120(no)), the sample rate is set to the selected sample rate, f s , and system parameters are updated (124). Updating system parameters includes automatic selection of a sampling rate, f s , that alters a characteristic output response in accordance with approximating a preselected desired output response for any order system in a manner demonstrated in FIG. 6, thereby automatically altering a damping coefficient related thereto. Then the process recycles to obtaining a further selected sample (108). 
     The control device adjustments on the controlled device provide a dynamic manipulation of control loop characteristics, eliminating the need for a dedicated control system microprocessor and allowing for flexibility in control system modification. Simultaneously, the efficiency of the control device is optimized. 
     FIG. 2, generally depicted by the numeral 200, sets forth a digital power control method utilizing a standard deviation algorithm. 
     In one embodiment, a beginning power input is determined (start) (202). A typical beginning power input value is zero. A predetermined minimum acceptable standard deviation value, Δ/2, a typical such value being plus or minus one decibel, is preset together with a desired predetermined maximum arithmetic mean value, μ set , for a difference between a selected sample and a sample previous thereto (204), a typical such deviation being ±0.5 dB. A predetermined minimum desired standard deviation value, sigma min , being a smallest value of: μ set  and Δ/2 is preset (206). 
     An output parameter of a controlled device is sampled N times (208), obtaining a plurality of samples, N, being at least a number of samples substantially equivalent to a quotient of a reciprocal of a bandwidth of a controlled system of the controlled device and a minimum conversion time predetermined and set by the control device. A typical output parameter sampled is output power of the controlled device, and the plurality of samples of sampled output parameter is obtained by successive sampling at a selected sample rate. 
     A standard deviation value of a preceding N samples, sigma N, and an arithmetic mean of the preceding N samples, μN, are determined (210). It is determined whether sigma N is less than or equal to sigma min  (212). When sigma N is not less than or equal to sigma min , updating system parameters by recycling (214) to setting sigma min  (206) and then sampling the output parameter N times (208) takes place. When sigma N is less than or equal to sigma min , delay of N sampling cycles, then recycling (216) to setting sigma  min  (206) and sampling the output parameter N times (208) takes place. In both cases recycling, μ set  is reset to an immediately preceding μN for an immediately preceding N samples. 
     The first comparison value may be selected to be a slope determined by determining a quotient of a difference between a selected sample and a sample obtained immediately previous thereto divided by a time lapse between those samples. 
     The second comparison value may be a slope determined by determining a quotient of a difference between a selected sample and a sample obtained immediately subsequent thereto divided by a time lapse between those samples. 
     Thus, controlling the sample rate as a function of the sampled output parameter may include the steps of: setting a maximum desired deviation for succesive samples of the output parameter; sampling a plurality of samples of sampled output parameter, substantially determined by a quotient of a reciprocal of a bandwidth of a controlled system of the controlled device and a minimum conversion time determined by the control device; obtaining the plurality of samples of sampled output parameter by a successive sampling at a selected sample rate; utilizing the plurality of samples of sampled output parameter to obtain a first primary correlation value; setting a minimum desired deviation as substantially a minimum of: the first primary correlation value and a desired maximum deviation; obtaining a plurality of samples of sampled output parameter, substantially determined by a quotient of a reciprocal of a bandwidth of a controlled system of the controlled device and a minimum conversion time determined by the control device, the plurality of samples of sampled output parameter being obtained by a successive sampling at a selected sample rate; and utilizing the plurality of samples of sampled output parameter to determine, substantially, a second primary correlation value and a secondary correlation value. 
     If the second primary correlation value of the plurality of samples of sampled output parameter is less than or equal to a minimum desired deviation, the control device disregards sampling a subsequent plurality of samples of sampled output parameter, substantially determined by a quotient of a reciprocal of a bandwidth of a controlled system of the controlled device and a minimum conversion time determined by the control device, the plurality of samples of sampled output parameter being obtained by a successive sampling at a selected sample rate, followed by recycling iteratively to set a minimum desired deviation as substantially a minimum of: the second primary correlation value and the desired maximum deviation, to obtain a succesive plurality of samples of sampled output parameter, substantially determined by a quotient of a reciprocal of a bandwidth of a controlled system of the controlled device and a minimum conversion time determined by the control device, to determine substantially a second primary correlation value and a secondary correlation value of the plurality of samples of sampled output parameter, and to compare. 
     If a secondary correlation value of the plurality of samples of sampled output parameter is greater than a minimum desired deviation, then the sample rate control means further causes the control device to activate a function to automatically alter the transfer function as a function of the sample rate, followed by recycling iteratively to set a minimum desired deviation as substantially a minimum of: the second primary correlation value and the desired maximum deviation, to obtain a successive plurality of samples of sampled output parameter, substantially determined by a quotient of a reciprocal of a bandwidth of a controlled system of the controlled device and a minimum conversion time determined by the control device, to determine substantially a second primary correlation value and a secondary correlation value of the plurality of samples of sampled output parameter, and to compare. In this case, at least one of the following is included: the first and second primary correlation values are arithmetic means of the immediately preceding plurality of samples of sampled output parameter; the secondary correlation value is a standard deviation of the immediately preceding plurality of samples of sampled output parameter; and the step of determining that the secondary correlation value is greater than the minimum desired deviation further includes altering the transfer function. 
     FIG. 3, generally depicted by the numeral 300, sets forth a block diagram of a microprocessor-based power control system of the present invention, depicting control system voltage input and radio frequency (RF) input (301) to a controlled device, typically a power amplifier (302). A sensor (306) provides feedback input to the power control device (308) that supplies a control system voltage to the controlled device (302). The control system voltage utilizes the sensor feedback input in accordance with the present invention to adjust amplification of a RF signal input supplied to the controlled device (302), such that an antenna (304) transmits a desired amplification of a RF signal. the power control (308), together with a power setting input control (312) and the sensor (306), make up a feedback device system (310) for implementing the present invention. The power control (308) may be set to a predetermined control voltage value by the power setting input control (312). 
     More particularly, a power control (308) together with a sensor (306) function as a control device (310) for controlling, at least in part, a controlled device (302), typically a power amplifier. 
     FIG. 4, generally depicted by the numeral 400, sets forth a block diagram of a closed loop feedback control system, including a forward signal flow path power set (401) for a power control system with a microprocessor (402), a D/A converter (404), a voltage level adjuster (406), a transducer (408), and a first transfer function (410), together with a feedback signal flow path with a sensor (416) and an A/D converter (414). The voltage level adjuster (406), together with the transducer (408) and the first transfer function (410), are aggregated to provide a second net transfer function (412) that is utilized with the sensor (416) to provide a power control input for the control device (402). A D/A converter and an A/D converter may be embodied within the power control unit or may be separate units as shown in FIG. 4. The controlled device has a first transform function (410), and is controlled, at least in part, by the control device. A D/A converter and an A/D converter may be embodied within a power control unit or may be separate units as shown in FIG. 4. 
     The control device adjustments on the controlled device provide a dynamic manipulation of control loop characteristics, controlling V out  (418), eliminating the need for a dedicated control system microprocessor, and allowing for flexibility in control system modification. Simultaneously, the efficiency of the control device is optimized. 
     FIG. 5, numeral 500, is a diagram illustrating root loci for a second order control system setting forth two selected sampling times in accordance with the invention. As is known in the art, the horizontal axis and the y axis depict, respectively, the Re, real, and jlm, imaginary, portions of a root locus, the unit circle (503) being displayed for comparison purposes. Root contours for periods, T=1 (501) and T=0.1 (501) are depicted on the root locus (504). It is clear that changing of the sampling period allows a predictable change in root locus for a second order control system, and suggests a similar response predictability in higher order control systems. 
     FIG. 6 is a graph setting forth a sampling time switching for a unit step power response of a second order system with respect to time in accordance with the present invention. As is known in the art, the x axis and y axis, respectively, represent time in seconds, and output, typically voltage. Clearly, the selected time periods, T=1 (601), T=2 (602), T=3 (603), T=4 (604), T=5 (605), and T=6 (606), allow for selection such that an output will be increased or decreased in accordance with the invention.