MXPA98010437A - Improved pilot detection for a control system that reduces distortion produced by electri circuits - Google Patents

Abstract

The present invention relates to an improved pilot detection technique for a control system comprising an electronic circuit that produces distortion and which applies the pilot signal to the electrical circuit and uses information obtained from the pilot signal to cancel the distortion of the signal. electrical circuit

Description

IMPROVED PILOT DETECTION FOR A CONTROL SYSTEM THAT REDUCES THE DISTORTION PRODUCED BY ELECTRICAL CIRCUITS BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention is directed to a control system for reducing distortion produced by electrical circuits and in particular to a control system using an improved pilot detection technique. DESCRIPTION OF THE RELATED ART Electric circuits in general often add undesirable distortion to a power signal, creating an output signal comprising distortion components and the power supply component. The distortion includes any unwanted signals that are added to or adversely affect the power signal. Therefore, there is a need to design techniques that can substantially eliminate or significantly reduce the distortion produced by electrical circuits. A well-known technique uses a control system and a pilot signal. The pilot signal is an electrical signal comprising at least one frequency component located spectrally close to the operating frequency band of the electrical circuit. REF: 28888 A more complete description of the pilot signal is illustrated in Figure 1. With reference to Figure 1, the frequency response of the electric circuit is illustrated to include the location of the pilot signal. The pilot signal may be near the lower edge of the operating band (for example pilot 1) or located near the upper edge of the operation band (for example pilot 2). The pilot is placed at a spectral distance of? F from an edge of the operating band with center frequency which is f0. The pilot signal can also be located somewhere within the operating band of the electrical circuit. It is readily apparent that the electrical characteristics (eg, amplitude, phase response, spectral content) of the pilot signal are known. It will be noted that although the pilot signal is illustrated as a single spectral component of a certain amplitude, the pilot signal may comprise a plurality of spectral components having various amplitudes. The control system reduces distortion produced by the electrical circuit by applying the pilot signal to the electrical circuit and making adjustments based on information obtained from the applied pilot signal. Figure 2 describes the control system and its use of information obtained from the pilot signal to reduce distortion produced by the electrical circuit 108. The electrical circuit 108 can be any electrical circuit having at least one power and one output. Let's say for example the electrical circuit 108 can be a linear Radio Frequency (RF) amplifier or a power amplifier. Still with reference to Figure 2, a feed signal is applied to the phase shifter 102. The shifter 102 replicates the feed signal on the paths 128 and 130. The shifter 102 is part of a loop with forward correction referred to as loop # 1, which in addition to phase shifter 102 comprises a Gain and Phase 104 circuit, coupler 132, electric circuit 108, delay circuit 106 and coupler 116. The feed signal in path 130 is applied to the Gain and Phase 104 circuit. Gain and Phase circuit 104 and the pilot signal are applied to the coupler 132. Typically, the amplitude of the pilot signal is much less (for example 30 dB less) than the amplitude of the power signal so as not to interfere with the operation of the circuit 108. The output of the coupler 132 is applied to the electrical circuit 108 whose output comprises the power signal, the pilot signal and the distortion signals produced by the circuit or electrical 108. A portion of the output of the electrical circuit 108 is obtained from the coupler 114 and combined with a delayed version of the power signal (signal in the path 127) in the coupler 116 via the connection path 115. The signal in the path 127 has experienced sufficient delay provided by the delay circuit 106, such that that signal experiences the same delay as the power signal that appears in the coupler 116 along the path 115. The Gain and Phase circuit 104 is controlled by the control path 134, with at least one control signal to adjust the gain and phase of the power signal, such that the power signal appearing on the coupler 116 along the path 115 is substantially the inverse (equal in amplitude but 180 ° out of phase) of the power signal. delayed feed in the coupler 116 along the path 127. The control signal appearing in the control path 134 of the Gain and Phase circuit 104 is derived from the signal at point A in a well-known manner, such as the use of detection circuits. The detection circuits detect well known electrical signal characteristics such as signal amplitude, phase and frequency. Therefore, the power signals applied to the coupler 116 substantially cancel each other leaving at point A the pilot signal and distortion signals produced by the electrical circuit 108. The loop # 1 in this manner is a loop with anticipated correction which serves to isolate at the point A the pilot signal and distortion signals produced by the electrical circuit 108.

The signals appearing at point A (pilot signals and distortion signals) are fed to the Gain and Phase 110 circuit whose output is fed to amplifier 112, whose output is applied to coupler 120 along path 126. A portion of the signals output (power signal, pilot signal and distortion signals) of the electrical circuit 108 is fed to the delay circuit 118 whose output is fed to the coupler 120 along the path 124. The delay circuit 118 is designed in such a way that the electrical circuit output signals 108 applied to the coupler 120 by the path 124, experience substantially the same delay as the electrical circuit output signals 108 applied to the coupler 120 by the path 126. Because the frequency, amplitude characteristics and other electrical characteristics of the pilot signal are known, the pilot detection circuit 140 can use circuits such as a mixer connected to a detector detector (or other well known detection circuits) to detect the pilot signal or a portion of the pilot signal by the coupler 138. The pilot signal is used to obtain information regarding the distortion produced by the electrical circuit 108 The information is obtained by detecting well-known electrical signal characteristics of the pilot signal. In particular, the characteristics (e.g., amplitude, spectral content, phase response) of the pilot signal are known and in this way when the pilot detection circuit 140 detects the pilot signal, some or all of the known characteristics may have been altered for the effects of distortion of the electrical circuit 108. The detection circuit 140 will detect said distortion effects and will use this information to generate control signals on the path 136 to cause the gain and phase circuit 110 to modify the pilot signal at the point A, such that the pilot signal on coupler 120 on path 126 is substantially the inverse (equal in amplitude, but 180 ° out of phase) of the pilot signal on coupler 120 on path 126. The corresponding pilot signals and the distortion signals in the coupler 120 are substantially canceled from each other in the coupler 120 leaving the signal of a installation (or an amplified version of the power signal) at the control system output. Therefore, loop # 2, comprising coupler 114, coupler 116, Gain and Phase 136 circuit, amplifier 112, coupler 120 and delay circuit 118 is a loop with forward correction using the information obtained from the pilot signal to substantially cancel out the distortion produced by the electrical circuit 108. In a current circuit, rarely there is an absolute cancellation of the distortion and pilot signals. In this way, the output signal of the control system of Figure 2 still contains some amount of relatively small distortion. The residual distortion that exists in the loop with forward correction (loop # 2) is also a result of the dynamic distortion characteristics that are exhibited by many electrical circuits such as the electrical circuit 108. The amplifier 112 also contributes distortion to the signal of departure. It is therefore convenient to detect the pilot signal and obtain information from the pilot signal to cancel the residual distortion. The output of the control system contains the pilot signal, despite being very small in amplitude compared to the output signal, which can be used to cancel the residual distortion of the loop with forward correction (loop # 2). Typically the amplitude of the pilot signal is relatively small compared to the output signal due to loop cancellation effects with forward correction # 2, as described above and the relative amplitude (also described above) of the pilot signal with respect to the amplitude of the power signal in the electrical circuit supply 108. In this way it becomes very difficult to detect the pilot signal at the output of the control system. One way to detect the pilot signal is to use a filter with very narrow or sharp and narrow spectral bandwidth. The use of a filter to detect the pilot signal is a very restrictive design since any change or deviation in the frequency and / or amplitude of the pilot signal, will require in design of another filter. Different filters have to be used with different pilot signals making the design and use of a control system with this design of pilot detection limiting and somewhat impractical. Also, the requirement to use different filters based on the selected pilot signal tends to complicate the design of the control system and increase the cost of this system. Therefore, in order to improve the effects of distortion cancellation of the control system of the Figure 2, there is a need to have a flexible design to detect the pilot signal without significantly contributing to the complexity and cost of the control system. COMPENDIUM OF THE INVENTION The present invention provides an improved pilot detection technique for a control system having a power, an output and comprising an electrical circuit that produces distortion when a pilot signal is applied to the electrical circuit and the pilot signal provides information which is used by the control system to substantially cancel the distortion. The control system comprises a loop with forward correction coupled to the control system to detect the pilot signal at the output of the control system where the control system obtains information from the pilot signal that the control system employs to cancel substantially any distortion residual. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a frequency response curve of an electrical circuit that shows the frequency within which the electrical circuit operates. Figure 2 is a block diagram of a prior art control system using a feedback loop and a loop with forward correction; Figure 3 is a block diagram of the present invention. DETAILED DESCRIPTION Now with reference to Figure 3, where like reference numbers identify similar or identical elements, Figure 3 illustrates the present invention wherein a loop with forward correction (loop # 3) is coupled to a control system (200 ) having a power, an output and comprising an electrical circuit that produces distortion, when the control system applies a pilot signal to the electrical circuit and obtains information from the pilot signal to reduce distortion produced by the electrical circuit.

The electrical circuit can be any circuit that has at least one power and one output. The loop with forward correction (loop # 3) detects the pilot signal at the output of the control system when the detected pilot signal provides information that is used by the control system to cancel substantially any residual distortion at the output of the control system. Still with reference to Figure 3, the control system 200 has a configuration of three loops wherein a pilot signal is applied to the electrical circuit 108 to which a first loop with forward correction (loop # 1) and a second loop with forward correction (loop # 2), they are coupled. When a power signal is applied to the phase shifter 102 and a pilot signal is applied to the electrical circuit 108 as illustrated, the output of the control system (signal path 224) comprises the power signal and a substantially attenuated pilot signal. The power signal that appears at the output of the control system contains distortion not completely canceled by loop # 2 of the control system. The present invention utilizes a third loop with forward correction to detect the substantially attenuated pilot signal, wherein the detected pilot signal provides information regarding any residual distortion and the information is used by the control system to substantially cancel the residual distortion. The information is obtained through the use of well-known detection circuits. The information may be for example alterations in amplitude, phase, frequencies suffered by the pilot signal that are detected by well-known detection circuits. The third loop with forward correction, labeled as loop # 3, comprises the coupler 202, coupler 116, Gain and Phase 110 circuit, amplifier 112, coupler 120, coupler 210, Gain and Phase 220 circuit, adder 214 and delay circuit 206. A portion of the output signal of the control system is obtained by the coupler 210 and applied to the Gain and Phase 220 circuit, whose output is applied to a feed of the adder 214 by the path 222. A portion of the feed signal delayed in the path 127 is obtained by the coupler 202 and applies to the delay circuit # 3 (206) whose output is applied to another power of adder 214 along path 208. Delay circuit # 3 is configured such that the delay experienced by the feed signal on path 208 becomes substantially equal to the delay experienced by the feed signal on path 222 In particular, the delay of the supply signal through phase shifter 1 2, Gain and Phase circuit 104, coupler 132, electric circuit 108, coupler 114, delay circuit 118, coupler 120, coupler 210 and Gain circuit and Phase 220 becomes substantially equal to the delay of the feed signal through phase shifter 102, delay # 1 (106) coupler 202 and delay # 3 (206).

The output of the adder 214 appearing in the path 216 is the algebraic sum of the signals appearing in the paths 208 and 222. The output of the adder 214 is detected through well-known circuits (eg energy detectors, phase detectors). , - not shown) and converted, through well-known means, to at least one control signal applied to the control path 212 of the Gain and Phase circuit. The control signals appearing in the control path 212 cause the Gain and Phase 220 circuit to modify the feed signal in the path 224 in such a way that it is substantially the inverse (equal in amplitude but 180 ° out of phase ) of the power signal in the path 208. When the two power signals are added with the use of the adder 214, they substantially cancel each other out. In short, the power signals and the pilot signal that appear in the output of the control system (path 224), they are added to a delayed power signal (on the path 208) by the adder 214 such that the power signals are substantially canceled from each other leaving the pilot signal and a substantially reduced feed signal in the path signal 216. The resulting pilot signal in the path 216 is detected through well-known means by detection circuits 218. For example, the detection circuits 218 may comprise a mixer connected to a log detector. The detected pilot signal is converted to at least one control signal in a well-known manner which is applied to the control path 136 of the Gain and Phase 110 circuit whose output is applied to the coupler 120 by the amplifier 112, to cancel out any distortion residual that is produced by the electrical circuit 108. The detected pilot provides information regarding the residual distortion and that information is used by the pilot detection circuit 218, to make the appropriate adjustments through the Gain circuit and Phase 110, to cancel substantially the residual distortion. The various circuits used in the loops # 1, 2 and 3 of the control of the present invention are well known to those of ordinary skill in the art to which the invention relates. Phase shifters such as phase shifter 102 are typically passive devices with a power supply and at least two outputs wherein the output signals are equal divisions or portions of an applied power supply signal. Delay circuits such as delay circuits 106, 206 and 118, are circuits that delay a power signal for a particular period of time. The adder 214 is a circuit having at least two feeds and one output and algebraically adding the amplitude and phase or energy of its power signals.

The Gain and Phase 104, 136 and 220 circuits are circuits that can modify the amplitude and phase of signals applied to their power supply based on the values of their control signals. The couplers 132, 202, 114 and 210 are circuits that can combine two or more signals and provide access to a portion of the combined signal. The detection circuits, although not illustrated, are well known circuits such as log detectors, null circuits and mixers. Log detectors are typically implemented as circuits that calculate the average amplitude of a signal applied to their power. Null circuits are typically implemented as circuits that can detect a power signal and generate control signals based on the detected power signal, where the control signals can be stored for future use. Other well-known circuits performing the functions described above can be used to implement the present invention. In addition, the circuits or their equivalents employed in the present invention can be implemented with electrical, electronic (digital and analog), optical and electromechanical devices. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following:

Claims (17)

1. CLAIMS 1. A control system having a power, an output, comprising an electrical circuit, which produces distortion when a pilot signal is applied to the electrical circuit and the pilot signal provides information that is used by the control system to substantially cancel the distortion; the control system is characterized by: a loop with anticipated correction coupled to the control system to detect the pilot signal at the output of the control system, when the control system obtains information from the pilot signal that the control system uses to cancel substantially any residual distortion. The control system according to claim 1, characterized in that the loop with anticipatory correction comprises an adder that algebraically adds signals to the control system output to a signal in the control system feed in order to detect the signal pilot. 3. The control system according to claim 2, characterized in that the power signal is delayed by a delay circuit. The control system according to claim 2, characterized in that the algebraic signal is obtained by the detection circuits that convert the sum to at least one control signal that is used to cancel substantially any residual distortion. 5. The control system according to claim 1, characterized in that the information is obtained from the detected pilot signal to substantially cancel the residual distortion with detection circuits. 6. The control system according to claim 1, characterized in that the signals at the output of the control system are modified by a Gain and Phase circuit, according to the control signals generated by the detection circuits. 7. A control system having a power, an output and comprising an electrical circuit that produces distortion, wherein a pilot signal applied to the electrical circuit provides information that the control system uses to substantially cancel the distortion, the control system is characterized by: a loop with anticipatory correction, which comprises a Gain and Phase circuit coupled to the output of the control system, an adder coupled to the Gain and Phase circuit, to detect the pilot signal at the output of the control system and a pilot detection circuit, for detecting the output of the adder that is converted to at least one control signal applied to the control system to substantially cancel out any residual distortion. The control system according to claim 7, characterized in that the adder detects the pilot signal by algebraically adding the output of the electrical circuit to a delayed power signal to the control system. 9. The control system according to claim 7, characterized in that the Gain and Phase circuit modifies the output of the control system in such a way that the pilot signal in a power supply of the electric circuit is substantially the inverse of the pilot signal that appears in another adder feed. The control system according to claim 9, characterized in that the adder has an output that is detected and converted to at least one control signal applied to the Gain and Phase circuit, causing the Gain and Phase circuit to modify the output of the electrical circuit. The control system according to claim 9, characterized in that the output of the adder is applied to a pilot detection circuit that converts the output of the adder to at least one control signal applied to the control system to cancel substantially any distortion residual. 12. A control system having an electrical circuit that produces distortion to which a pilot signal is applied, the control system is characterized in that it comprises: a first loop with forward correction coupled to the electrical circuit to isolate the pilot signal and the distortion, - a second loop with forward correction coupled to the first loop with forward correction to obtain information from the isolated pilot signal and use the information to substantially cancel out the distortion; and a third loop with forward correction coupled to the first and second loops with forward correction to detect the pilot signal of the second loop with forward correction and use information obtained from the pilot signal to cancel substantially any residual distortion. The control system according to claim 12, characterized in that the pilot signal is detected by algebraically adding the output of the second loop with anticipatory correction to a delayed feed of the control system with an adder. The control system according to claim 13, characterized in that the third loop with forward correction has a Gain and Phase circuit coupled to a second loop with forward correction, wherein the Gain and Phase circuit modifies signals from the second loop with anticipatory correction according to control signals generated from the adder output. The control system according to claim 13, characterized in that the detected pilot signal is converted to at least one control signal by a pilot detection circuit coupled to the adder and wherein the control signal at least applies to the second loop with anticipatory correction to substantially cancel out any residual distortion. 16. A method for detecting a pilot signal applied to an electrical circuit that produces distortion, wherein the electrical circuit is coupled to a control system having a power and an output, wherein the control system obtains information from the pilot signal to substantially cancel the distortion, the method is characterized in that it comprises the steps of: applying a power signal to the power supply of the control system; and add the output of the control system to the power signal with an adder that has a power and an output. 17. The method of compliance with the claim 16, characterized in that the adding step further comprises the steps of retarding the feed signal; and modifying the output of the control system, based on at least one control signal generated from the adder output.