Abstract:
A feed-forward amplifier having a signal cancellation loop including a cancellation node that includes a gain controller and a phase controller. Each controller provides a discrete tap steering signal and modulates the corresponding tap steering signal with a discrete tracer signal that takes on a preselected sequence of values. The sequence chosen so that the tracer signal is mutually orthogonal to each other tracer signal over a preselected period. A gain and phase adjuster connected to the outputs of the controllers provides a controlled gain change and phase shift in the signal cancellation loop, the magnitude of the gain change and phase shift controlled by the corresponding tap steering signals presented to the gain and phase adjuster by the controllers. A detector, the input of which is connected to the cancellation node and the output of which is connected to the controllers, outputs a measure of the envelope of the signal at the cancellation node. After the preselected period new values for the tap steering signals presented to the gain and phase adjuster by the controllers are obtained by multiplying detector output by the respective tracer signal, each over the respective preselected period, summing each resulting series of values, and changing the tap steering signals to be modulated and presented to the gain and phase adjuster in accordance with the values of the respective sums.

Description:
PRIORITY CLAIM 
     The present application claims priority from each of U.S. provisional patent application No. 60/311,358, filed Aug. 13, 2001 and from U.S. non-provisional patent application Ser. No. 10/016,691, filed Dec. 17, 2001, the contents of both of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to adaptive circuits. More specifically, the present invention relates to an apparatus and method for controlling adaptive circuits, such as controlling gain and phase adjustments in a feed forward amplifier circuit. 
     BACKGROUND OF THE INVENTION 
     Adaptive circuits are well known and used in a variety of applications. One well-known example of an adaptive circuit is the feed forward amplifier (“FFA”). In order to achieve linearity in a feed forward amplifier, careful control of the amplifier circuitry is required. In particular, in FFAs two or more gain and phase adjusters are often employed and the taps of each of these adjusters are carefully steered to achieve linearity through the amplifier. 
     Within the art of FFAs, it is known to use detector-controller circuits, one for each gain-and-phase adjuster. Each detector-controller circuit is operable to steer the taps of its respective gain-and-phase adjuster in the FFA so that the main amplifier and correctional amplifier can properly cooperate in order to reduce error introduced by the main amplifier and, should a pilot tone be used in the FFA, to also reduce the output residue of the pilot tone injected prior to the main amplifier. 
     In certain prior art detector-controller circuits, once the detector portion of the detector-controller circuit has indicated that the associated controller portion should make an adjustment, the controller arbitrarily steers the taps of the gain-and-phase adjuster in a direction to either increase or decrease the input to the tap, without knowing which of an increase or decrease will actually achieve the desired effect. In order to verify whether the controller steered the tap in the correct direction (e.g., to increase the signal to the tap), after the correction has been applied the detector circuit ascertains whether the direction of the variation brought about the desired effect, and, if so, instructs the controller circuit to continue steering in the same direction, if necessary. If, however, the detector circuit ascertains that the steering direction brought about an undesired result, then the detector instructs to the controller to try steering the tap in the opposite direction (e.g., to decrease the signal to the tap). 
     In the prior art, each detector-controller circuit works independently of each other, and therefore, achieving convergence towards an optimum level for each tap of each adjuster can be difficult. For example, rapid changes in the strength of the input signal being amplified by the FFA can make it difficult for the detector-controller circuits to respond quickly enough to converge the tap levels of each gain-and-phase adjuster towards the respective optimum levels. Furthermore, the adjustment of one tap of a gain-and-phase adjuster can disrupt an optimum or near optimum input level achieved at another tap, therefore cascading disruptions through all of the taps. 
     The inventor of the present invention also believes that a further problem is that such prior art controller circuits can sometimes result in taps being steered to levels that are levels corresponding to local minima for the input signal, missing a global optimum for the input signal. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a novel apparatus and method for controlling an adaptive circuit that obviates or mitigates at least one of the above-identified disadvantages of the prior art. It is a further object of the present invention to provide a novel feed forward amplifier that obviates or mitigates at least one of the above-identified disadvantages of the prior art. 
     According to an aspect of the present invention, there is provided a feed-forward amplifier having a signal cancellation loop including a cancellation node that includes a gain controller and a phase controller. Each controller provides a discrete tap steering signal and modulates the corresponding tap steering signal with a discrete tracer signal that takes on a preselected sequence of values. The sequence chosen so that the tracer signal is mutually orthogonal to each other tracer signal over a preselected period. A gain and phase adjuster connected to the outputs of the controllers provides a controlled gain change and phase shift in the signal cancellation loop, the magnitude of the gain change and phase shift controlled by the corresponding tap steering signals presented to the gain and phase adjuster by the controllers. A detector, the input of which is connected to the cancellation node and the output of which is connected to the controllers, outputs a measure of the envelope of the signal at the cancellation node. After the preselected period new values for the tap steering signals presented to the gain and phase adjuster by the controllers are obtained by multiplying detector output by the respective tracer signal, each over the respective preselected period, summing each resulting series of values, and changing the tap steering signals to be modulated and presented to the gain and phase adjuster in accordance with the values of the respective sums. Optionally, each tap steering signal may be increased or decreased depending upon the polarity of the corresponding sum, or the tap steering signal presented to the gain and phase adjuster is left unchanged if the corresponding sum is zero or within a preselected range about zero but, if the corresponding sum is outside the preselected range about zero, is increased or decreased depending upon the polarity of the corresponding sum. Also, each tap steering signal is increased if the corresponding sum is positive and decreased if the corresponding sum is negative. In any of the embodiments discussed above, the tracer signals vary in polarity but not in magnitude and may be chosen to be pseudo noise sequences or Walsh codes. 
     According to another aspect of the present invention, there is provided a feed-forward amplifier that includes:
         an input port;   a first main path splitter, the input of which is connected to the input port so that when an input signal applied to the input port it is split by the first main path splitter into a main signal and a feed-forward signal;   a main signal path gain and phase adjuster, the input of which is connected to the first output of the first main path splitter, the main signal path gain and phase adjuster having a gain-control input tap and a phase-control input tap configured so that the voltage levels on the taps control the amplitude and phase of the main signal;   a main amplifier, the input of which is connected to the output of the main signal path gain and phase adjuster;   a second main path splitter, the input of which is connected to the output of the main amplifier;   a feed-forward signal path delay element, the input of which is connected to the second output of the first main path splitter, the delay imposed by the feed-forward signal path delay element selected to approximately match the delay in the main signal caused by the main amplifier;   a feed-forward path coupler, the first input of which is connected to the output of the feed-forward signal path delay element;   a connector/attenuator connecting the second output of the second main path splitter to the second input of the feed-forward path coupler, the attenuation selected so that the undistorted portion of the main signal provided to the feed-forward path coupler is approximately cancelled out by the feed-forward signal;   a feed-forward path splitter, the input of which is connected to the output of the feed-forward path coupler;   a detector, the input of which is connected to the second output of the feed-forward path splitter;   a gain controller, the input of which is connected to the output of the detector and the output of which is connected to the gain-control input tap; and   a phase controller, the input of which is connected to the output of the detector and the output of which is connected to the phase-control input tap,
 
wherein:
       each of the controllers modulates the voltage level on its respective output with a discrete low level signal that takes on a preselected sequence of values, the sequence chosen so that each low level signal is mutually orthogonal to each other low level signal over a preselected period; the detector outputs a measure of the envelope of the signal at the cancellation node; and each controller multiples the signal received from the detector by the low level signal with which it modulated the tap to which it is connected, in each case over the preselected period, sums the resulting series of values over time, and changes the voltage level on its respective tap in accordance with the value of the sum.   

     Optionally, each voltage level is increased or decreased depending upon the polarity of the corresponding sum or the voltage level presented to the gain and phase adjuster is left unchanged if the corresponding sum is zero or within a preselected range about zero but, if the corresponding sum is outside the preselected range about zero, is increased or decreased depending upon the polarity of the corresponding sum. Also, each voltage level may be increased if the corresponding sum is positive and decreased if the corresponding sum is negative and each output voltage level may be changed in proportion to magnitude of the respective sum. 
     In any of the embodiments discussed above, the low level signals vary in polarity but not in magnitude and the low level signals may be chosen to be pseudo noise sequences or Walsh codes. 
     According to yet another aspect of the present invention, there is provided a feed-forward amplifier having a signal cancellation loop including a cancellation node at which a signal is to be minimized, including:
     a controller for providing a tap steering signal and modulating the tap steering signal with a tracer signal that takes on a preselected sequence of values;   an adjuster connected to the output of the controller for providing a controlled change in a characteristic of the signal cancellation loop that results in a change in a measure of the envelope of the signal at the cancellation node, the magnitude of the change in the characteristic controlled by the modulated tap steering signal presented to the adjuster by the controller; and   a detector, the input of which is connected to the cancellation node and the output of which is connected to the controller, the detector for outputting the measure of the envelope of the signal at the cancellation node,   wherein after the preselected period a new setting for the tap steering signal is obtained by multiplying the detector output by the tracer signal, summing the resulting series of values, and changing the tap steering signal to be modulated and provided to the adjuster in accordance with the value of the sum.   

     Optionally, the tap steering signal may be increased or decreased depending upon the polarity of the corresponding sum, or the tap steering signal presented to the gain and phase adjuster is left unchanged if the corresponding sum is zero or within a preselected range about zero but, if the corresponding sum is outside the preselected range about zero, is increased or decreased depending upon the polarity of the corresponding sum. Also, the tap steering signal is increased if the corresponding sum is positive and decreased if the corresponding sum is negative. In any of the embodiments discussed above, the tracer signal vary in polarity but not in magnitude and may be chosen to be pseudo noise sequences or Walsh codes. 
     According to yet another aspect of the present invention, there is provided a circuit having a node at which a signal is adaptively minimized by the circuit, comprising: a controller providing an output voltage level, the output voltage level modulated by a low level signal that takes on a preselected sequence of values over a preselected period; an adjuster connected to the output of the controller for providing a controlled change in a characteristic of the adaptive circuit that results in a change in a measure of the envelope of the signal at the node, the magnitude of the change in the characteristic controlled by the voltage level presented to the adjuster by the controller; and a detector, the input of which is connected to the node and the output of which is connected to the controller, the detector outputting the measure of the envelope of the signal at the node, wherein after the preselected period a new setting for the voltage level presented to the adjuster by the controller is obtained by multiplying the detector output by the low level signal, summing the resulting series of values, and changing the voltage level presented to the adjuster in accordance with the value of the sum. 
     Optionally, each voltage level is increased or decreased depending upon the polarity of the corresponding sum or the voltage level presented to the adjuster is left unchanged if the corresponding sum is zero or within a preselected range about zero but, if the corresponding sum is outside the preselected range about zero, is increased or decreased depending upon the polarity of the corresponding sum. Also, each voltage level may be increased if the corresponding sum is positive and decreased if the corresponding sum is negative and each output voltage level may be changed in proportion to magnitude of the respective sum. 
     According to yet another aspect of the present invention, there is provided a feed forward amplifier comprising: 
     an amplifier portion including a coupler, first and second gain and phase adjusters, first and second delay elements, a main amplifier and a correctional amplifier, the coupler providing an input signal to said amplifier portion to a first signal path including the first gain and phase adjuster, the main amplifier and the first delay element and an output and the coupler providing the input signal to a second signal path including the second delay element, the second gain and phase adjuster and the correctional amplifier having a first signal path for carrying an input signal to a first gain-and-phase adjuster and a main-amplifier, said first gain-and-phase adjuster having a pair of taps for steering said first adjuster, said amplifier portion having a second signal path for carrying a sample of said input signal generated to a second gain-and-phase adjuster and a correctional-amplifier, said second gain-and-phase adjuster having a pair of taps for steering said adjuster; and 
     a detector-controller portion having a first detector for receiving a detected signal from said first signal path and a second detector for receiving a detected signal from said second signal path, said detector-controller portion further comprising a first pair of controllers for receiving said detected signal from said first detector and a second pair of controllers for receiving said detected signal from said second detector, said controllers each operable to steer a respective one of said taps based on said received detected signals, each of said controllers further operable to inject tracer-signals into its respective tap, said tracer-signals for carrying through said amplifier portion and modulating said detected signals, said controllers each operable to extract from its respective detected signals a tap-signal by using its respective said tracer-signal, said controllers each further operable to utilize said extracted tap-signal to determine a desired direction for steering its respective tap and to output, substantially simultaneously with each other controller, a signal to steer said respective tap. 
     According to yet another aspect of the present invention, there is provided a feed forward amplifier comprising: an amplifier portion including:
         (a) a first signal path having a first gain and phase adjuster, a main amplifier and a delay element; and   (b) a second signal path having a delay element, a second gain and phase adjuster and a correctional amplifier, each gain and phase adjuster including a control input tap to accept an input to alter the phase response of the gain and phase adjuster and a control input tap to accept an input to alter the gain response of the gain and phase adjuster, the first and second signal paths having a common signal input and a common signal output; and
 
a detector portion including:
   (c) a first detector to receive a signal from the common signal output and to provide the received signal to a first controller operable to create an input to the gain tap of the second gain and phase adjuster and to provide the received signal to a second controller operable to create an input to the phase tap of the second gain and phase adjuster; and   (d) a second detector to receive a signal from the second signal path before the second gain and phase adjuster and to provide the received signal to a first controller operable to create an input to the gain tap of the first gain and phase adjuster and to provide the received signal to a second controller operable to create an input to the phase tap of the first gain and phase adjuster, each controller responsive to a component in said received signals which is orthogonal to the components to which each other controller are responsive to and all the created inputs being applied to the taps substantially simultaneously and altering the operation of said feed forward amplifier to linearize the amplification of the input signal through the feed forward amplifier.       

     According to yet another aspect of the present invention, there is provided a method for operating an adaptive control circuit having a plurality of control input taps, said method comprising, for each said control input, the steps of: detecting a signal, including a tracer signal, from said circuit; extracting a measurement from the tracer signal in said detected signal; determining an appropriate input to be applied to said control input to improve operation of said adaptive circuit; creating a tracer signal for said control input, said created tracer signal being orthogonal to the tracer signals created for each other control input; and combining said tracer signal and said determined input and applying the resulting signal to said control input. 
     An apparatus and method for operating an adaptive circuit includes injecting a set of orthogonal tracer signals into the circuit. The tracers&#39; signals are extracted after modification during operation of at least a portion of the circuit and are examined by respective controllers to modify operation of the circuit. 
     In one embodiment, the invention is incorporated into a feed forward amplifier in which a set of orthogonal tracer signals is applied to the amplifier. A detector controller detects a signal including as components the orthogonal tracer signals as modified by portions of the amplifier. Each controller portion of the detector controller extracts a measurement relative to its respective tracer signal from the detected signal and modifies its output to control a portion of the amplifier accordingly. The controllers apply their outputs to the respective portions of the amplifier at substantially the same time, leading to quick convergence of the operating point of the amplifier to an optimal, or near-optimal, configuration. Injection of the tracer signals into the amplifier is accomplished by dithering the controller outputs by the respective orthogonal tracer signals. 
     According to yet another aspect of the present invention, there is provided an adaptive circuit comprising: 
     at least two adjusters, each adjuster including at least one control input to alter the operation of the circuit; 
     at least one signal generator to create at least one tracer signal, each created tracer signal being orthogonal to each other created tracer signal; 
     at least two controllers, each controller operable to output a control signal to at least a respective one of the control inputs of the at least two adjusters, a different orthogonal tracer signal from said at least one signal generator being applied to each respective control signal as a dither; and 
     at least one detector operable to extract a composite signal from the circuit and to apply the composite signal to the at least two controllers, each controller being responsive to the applied signal to extract at least one orthogonal tracer and alter the respective control signal to converge operation of the circuit to an optimal or near optimal configuration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein: 
         FIG. 1  is a block diagram of a feed forward amplifier in accordance with an embodiment of the present invention; 
         FIG. 2  is a block diagram of a detector-controller portion of the amplifier shown in  FIG. 1 ; 
         FIG. 3  is a flow chart showing a method of controlling the gain and phase adjustment of the amplifier of  FIG. 1 ; 
         FIG. 4  is an exemplary set of Walsh codes for use in the detector-controller portion of the amplifier of  FIGS. 1 and 2 ; 
         FIG. 5  shows an example of the operation of two of the controllers shown in  FIG. 2  using the method of  FIG. 3 , during an initial power-on of the amplifier of  FIG. 1 ; and 
         FIG. 6  shows an example of the operation of the controllers shown in  FIG. 5  during a subsequent iteration through the method shown of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1 , a forward feed amplifier (“FFA”) in accordance with an embodiment of the invention is indicated generally at  20 . FFA  20  comprises an amplifier portion  24  and a detector-controller portion  28 . Amplifier portion  24  includes a coupler  36  that is connected to an input signal path  40 . Coupler  36  is operable to split an incoming signal from path  40  into a main amplifier signal path  44  and a correctional amplifier signal path  48 . 
     Main amplifier signal path  44 , which carries the main signal from coupler  36 , includes a gain and phase adjuster GPA 1 , a main amplifier  56  and a delay element  60  that outputs to an output signal path  64 . GPA 1  includes a gain control input tap T 1 , and a phase control input tap T 2 , each of which can be steered so that GPA 1  operates to yield maximum signal cancellation at the output of coupler  82  and the input of coupler  104 , as discussed below. The location in the circuit at which maximum signal cancellation is to occur is sometimes referred to as the “cancellation node”. 
     Correctional amplifier signal path  48  which carries a sample, generated by coupler  36 , of the signal from input signal path  40  includes a delay element  68 , a gain and phase adjuster GPA 2  and a correctional amplifier  74 , the output of which connects to output signal path  64  via a coupler  76 . GPA 2  includes a gain control input tap T 3 , and a phase control input tap T 4 , each of which can be steered so that GPA 2  is adjusted to require a minimum, or near minimum, amount of power to be delivered to the correctional amplifier  74 . As used herein, the terms “steer”, “steered” and “steering” are intended to comprise all suitable methods of adjusting and/or controlling of the taps respective to a gain and phase or other suitable adjuster. In the embodiment of the invention discussed below, taps T 1 , T 2 , T 3 , and T 4 , are steered by changing the voltage levels applied to each of them respectively. 
     As will be apparent to those of skill in the art, GPA 2  and correctional amplifier  74  form an error pathway  73  within amplifier portion  24 . Accordingly, when the output of correctional amplifier  74  is coupled to the output of delay  60 , errors and pilot tones, if used, are substantially eliminated from the output signal path  64 , such that the output signal path  64  presents a substantially linear amplification of the signal from input signal path  40 . 
     Amplifier portion  24  is further characterized by a coupled path  79  that interconnects a first coupler  80 , which is connected to the output of main amplifier  56 , and a second coupler  82 , which is connected to the output of delay element  68 , in order to provide a sample of the error introduced by main amplifier  56  to the error pathway  73 , commencing at GPA 2 . Attenuation may be provided in coupled path  73 , if not already provided by the first coupler  80 . 
     The main amplifier signal path  44 , the correctional amplifier signal path  48 , and the coupled path  79  together are sometimes referred to as a “signal cancellation loop”. 
     In the illustrated embodiment, amplifier portion  24  further includes a pilot tone generator  86  that is coupled, via a coupler  90 , to the input of main amplifier  56 . Pilot tone generator  86  generates a pilot tone for use by error pathway  73  in the usual manner for reducing error introduced by main amplifier  56 . By the same token, amplifier portion  24  further includes a pilot tone receiver  94  that is coupled, via a coupler  98 , to output signal path  64 . Pilot tone receiver  94  is operable to measure any remaining pilot tone present along output signal path  64  for eventual use by error pathway  73  to introduce a signal at coupler  76  that will reduce the pilot tone in output signal path  64 . 
     Detector-controller portion  28  connects to amplifier portion  24  through various inputs and various outputs, as described herein. Specifically, a coupler  104  connected just prior to error pathway  73  delivers an input signal to a first detector D 1 , which in turn presents a detector-output to a gain controller C 1  and a phase controller C 2 . In the illustrated embodiment, the detector-output is a measure of the amplitude of the envelope of the input signal applied to it. However, it is within the scope of the invention to provide as a detector-output a signal proportional to the log of the RMS value of the envelope of the input signal or proportional to peaks of the envelope of the input signal, as well as any other measure or signal that will occur to those skilled in the art. Wherever in the following or in the claims that reference is made to the detector-output being the amplitude of the envelope of the input signal applied to it, it should be understood that such other signals or measures are also intended. 
     Similarly, pilot tone receiver  94  delivers an output signal to a second detector D 2 , which in turn presents a detector-output to a gain controller C 3  and a phase controller C 4 . Again, detector D 2  outputs the amplitude of the envelope of the input signal applied to it. As will be discussed in greater detail below, controllers C 1 , C 2 , C 3  and C 4  are operable to steer taps T 1 , T 2 , T 3  and T 4 , respectively, based on the signals received from their respective detectors D, in order to find optimum (or otherwise desired) gain and phase adjustments for each of adjusters GPA 1  and GPA 2 . 
     In the illustrated embodiment, tracer signals are applied to each of main amplifier signal path  44  and correctional amplifier signal path  48  by using them to modulate the voltage levels applied to the taps T 1 , T 2 , T 3 , and T 4 , respectively. Those voltage levels are also referred to as tap steering signals and the modulated voltage levels as modulated tap steering signals. Each tracer signal, because it rapidly but slightly changes either the gain or the phase in the signal cancellation loop, causes variations in the amplitude of the envelope of the input signal applied to one of the detectors D 1  and D 2 . The detected amplitudes of the envelopes of the signals applied to the detectors D 1  and D 2  are passed to the respective controllers C. Each controller C extracts the variation in the detector output caused by the tracer signal applied to the corresponding tap and steers the tap accordingly. The variations in the detector outputs caused by the tracer signals can be separated from each other because each tracer signal is selected to be orthogonal to each other tracer signal. As described below, to achieve orthogonality in the illustrated embodiment each tracer signal is a Walsh code, but other techniques, such as selecting appropriate pseudo noise sequences as the tracer signals will be apparent to those of skill in the art. As will become apparent to those of skill in the art from the discussion herein, the present invention will operate with tracer signals that are not totally orthogonal to each other, although better performance will be obtained when using signals as orthogonal as possible. Accordingly, as used herein, the term orthogonal is intended to include both perfectly orthogonal signals, such as Walsh codes, and near-orthogonal signals, for example pseudo noise sequences taken over a time period that provides approximately orthogonal results. The general criterion is that the more uncorrelated tracer signals are over an appropriate time period the better the results. 
     Before going into the details, as an overview, consider an idealized situation that may help in understanding the embodiment of the invention described herein. To aid in understanding, we assume that the main amplifier does not distort the input signal at all and we start with adjusting only one tap steering signal. We begin by setting a tap steering signal at a particular voltage level. If that voltage level is applied to a tap of an adjuster, a particular level of signal cancellation at the cancellation node results. If the voltage level is optimal (so that the amplitude of envelope of the signal at the cancellation node is zero), dithering of the voltage level by a tracer signal that has an average value of zero (as do orthogonal and pseudo noise sequences over appropriate periods) will result in slight excursions in the amplitude of envelope of the signal at the cancellation node above and below zero, but the sum of all the excursions will be zero. Now suppose that the voltage level is not optimal. Then the slight excursions in the amplitude of the envelope of the signal at the cancellation node will be to levels above and below the amplitude of envelope of the signal at the cancellation node that would occur if no dither were applied. The result will be a non-zero sum with a polarity, or sign, the same as the polarity of the amplitude of the envelope of the signal at the cancellation node would be if no dither were applied. So far we have assumed that there is only one tap. If there are more taps, then by using orthogonal or pseudo noise sequences over appropriate periods as tracer signals, the excursions in the amplitude of envelope of the signal at the cancellation node caused by dithering of each tap can be extracted separately from the amplitude of envelope of the signal at the cancellation node, summed, and used to adjust the corresponding tap steering signals simultaneously. 
     Referring now to  FIG. 2 , detector-controller portion  28  will now be discussed in greater detail. As shown, controllers C 1 , C 2 , C 3  and C 4  each include the same components. Each controller C includes a multiplier  200  that receives a detector-output from a respective detector D. Controllers C are operable to utilize the detector-output to determine how to steer their respective tap T. In the present embodiment, each detector-output is the amplitude of the envelope of the signal received by a respective detector D and carries combined information about the effects of dithering (modulating) the respective tap steering signals with the respective tracer signals on the amplitude of the envelope of the signal received by the respective detector D. The information carried about the effect of the dithering of each tap steering signal with a tracer signal may be separately extracted from the detector-output in the manner discussed in greater detail further below. 
     To extract the effect of the tracer signal injected by tap T for the controller C, each multiplier  200  receives its Walsh code from a Walsh code generator  204 . Each Walsh code generator  204   1 ,  204   2 ,  204   3  and  204   4 , generates a unique Walsh code, which, as is understood by those of skill in the art, is a preselected pattern of one or more logical ones and/or logical zeroes that repeat over a given period and is orthogonal to each other Walsh code. As will be discussed in greater detail below, when the detector-output from a respective detector D is multiplied by multiplier  200  with a respective Walsh code, only the portion of the detector-output resulting from the tracer signal injected at the respective tap T will be output from the respective multiplier  200 . 
     Controllers C also each include an integrator  208  which is operable to sum the results from multiplier  200 , which represent the effect of tracer signal for the respective tap T on the respective detector-output, for each period and output those summed results to an adjuster  212  which is operable to determine from the summed result whether the tap T it is responsible for is properly steered. If an adjuster  212  determines that its corresponding tap T was steered in the proper direction, then adjuster  212  outputs a signal that continues to steer that tap T in the same direction. If adjuster  212  determines that its corresponding tap T was steered in the wrong direction, then adjuster  212  outputs a signal that steers that tap T in the opposite direction. Adjuster  212  can also determine that the tap T is at an optimum level, in which case adjuster  212  does not steer tap T at all, but leaves the tap steering signal at the existing level. Further details of adjuster  212  will be discussed in greater detail below. 
     To inject the tracer signal for a controller C into amplifier portion  24 , the signal outputted from adjuster  212  is modulated, using a summer  216 , with the Walsh code generated at Walsh code generator  204 , the Walsh code having first been attenuated through an attenuator  220  by a factor A. The Walsh code is attenuated, by factor A, to a level that provides a suitable “dither” or “perturbance” that can be summed with the control signal from adjuster  212  for the respective tap T. The voltage level of the resulting modulated signal is at a level that will generally yield a minimum reliably detectable signal at the output of detector D. 
     As will be apparent to those of skill in the art, in order for the Walsh code to behave as a good dither, each Walsh code for each controller C is selected to have as many transitions as possible, while still being orthogonal to the Walsh codes of the other controllers C. Also, as the tracer signal is averaged over a suitable period of time to reduce the effects of noise in the detected signal, it is desired to choose a Walsh code, or other orthogonal signal, with a suitably long length. It is presently preferred that a length for the Walsh codes is selected which is at least twice the number taps T to be controlled, i.e.—in the embodiment of  FIG. 1 , the shortest desired length of Walsh codes would be an eight chip code and, in fact, it is presently preferred to use a Walsh code length of sixty-four chips for a feed forward amplifier with four taps T. 
     The output of each summer  216  is then presented to its respective tap T, thereby steering each respective tap T accordingly and injecting the respective tracer signal. 
     A method of controlling the gain and phase adjustment of feed forward amplifier  20  will now be discussed with reference to  FIG. 3 . The flow-chart in  FIG. 3  shows a sequence of steps which can be used to operate, for example, each controller C of detector-controller portion  28 , thereby steering each tap T. In other words, the sequence of steps in  FIG. 3  will be performed, in parallel, for each controller C. 
     Although, as mentioned above, in a presently preferred embodiment each Walsh code is actually sixty-four chips in length, for simplicity while explaining the method, it will be assumed that each Walsh code W 1 , W 2 , W 3  and W 4 , is only eight chips in length. Each Walsh code W 1 , W 2 , W 3  and W 4  is generated by a respective Walsh code generators  204   1 ,  204   2 ,  204   3  and  204   4  and is shown in Table I and illustrated in the pulse-waveforms shown in  FIG. 4 . From the waveforms shown therein, it is to be understood that a “1” means a logical “1”, and “−1” means a logical “0”. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                 Chip 
                 W 1   
                 W 2   
                 W 3   
                 W 4   
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 2 
                 −1 
                 −1 
                 1 
                 −1 
               
               
                 3 
                 −1 
                 1 
                 −1 
                 −1 
               
               
                 4 
                 1 
                 −1 
                 −1 
                 1 
               
               
                 5 
                 −1 
                 1 
                 1 
                 1 
               
               
                 6 
                 1 
                 −1 
                 1 
                 −1 
               
               
                 7 
                 1 
                 1 
                 −1 
                 −1 
               
               
                 8 
                 −1 
                 −1 
                 −1 
                 1 
               
               
                   
               
             
          
         
       
     
     Again for simplicity, the method of  FIG. 3  will only be discussed in detail with reference to controllers C 1  and C 2  and their associated detector D 1 . The method begins at step  300  where a signal is detected at detector D 1  from the amplifier portion  24  of feed forward amplifier  20 . To illustrate how this step can be accomplished according to a present embodiment, it will be assumed that feed forward amplifier  20  has just been activated (i.e. initialized), but that no input signal is present along input signal path  40 , and accordingly no output signal is present along output signal path  64 . 
     The activity in feed forward amplifier  20  at this point in the method is illustrated in  FIG. 5 , where detector D 1 , controller C 1  and controller C 2  are shown. As there is no input signal along input signal path  40 , detector D 1  detects this and outputs a corresponding waveform, which is represented in  FIG. 5  as a detector-output waveform  400   a , which in turn is inputted into multiplier  200   1  and multiplier  200   2 . 
     By way of further background to the operation of the present embodiment, it will be apparent to those of skill in the art that the tracer signal being applied to the taps T of gain and phase adjuster GPA 1 , whether a Walsh code or any other dither, will only be detectable at detector D 1  where there is an input signal along input signal path  40  as the tracer signal is a modulation of the input signal. Similarly, if a pilot tone is being injected at coupler  90 , then the tracer signal applied at the taps T of GPA 2  will be detectable at detector D 2  as modulation of the pilot tone detected at detector D 2 . As there is as yet no input signal in  FIG. 5 , detector-output waveform  400   a  is all zeros, as shown. 
     Referring again to  FIG. 3 , the method then advances to step  320  where the tracer signal for the tap T 1  respective to the controller C 1  is extracted from the signal detected at step  300 . In a present embodiment, this signal is extracted from detector-output waveform  400   a  using multiplier  200  and integrator  208 . First, multiplier  200  multiplies the Walsh code output from Walsh code generator  204  with the detector-output waveform  400   a  to extract the tracer signal. The product waveform is presented to integrator  208 , which sums each pulse in the waveform over the number of chips in the Walsh code. The output for each integrator  208   1 ,  208   2  are represented on  FIG. 5  as items  404   a   1  and  404   a   2 , respectively. 
     Specifically, for controller C 1 , since the detector-output  400   a ={0, 0, 0, 0, 0, 0, 0, 0 }, and since the output of Walsh code generator  204   1  can be represented by the series W 1 ={1, −1, −1,1,−1,1,1,−1}, then the output of multiplier  200   1  can be represented as {0, 0, 0, 0, 0, 0, 0, 0}×{1, −1, −1, 1, −1, 1, 1, −1}=(0, 0, 0, 0, 0, 0, 0, 0). The result  404   a   1 , from integrator  208   1  can be represented as  404   a   1 =(0, 0, 0, 0, 0, 0, 0, 0)=0. 
     Similarly, for controller C 2 , since detector-output  400   a ={0, 0, 0, 0, 0, 0, 0, 0} and since the output of Walsh-code generator  204   2  can be represented by the series W 2 ={1, −1, 1, −1, 1, −1, 1, −1}, then the output of multiplier  200   2  can be represented as {0, 0, 0, 0, 0, 0, 0, 0}×{1, −1, 1, −1, 1, −1, 1, −1}=(0, 0, 0, 0, 0, 0, 0, 0). The result  404   a   2 , from integrator  208   2  can be represented as  404   a   2 =(0, 0, 0, 0, 0, 0, 0, 0)=0. 
     Referring again to  FIG. 3 , the method then advances to step  340  where the appropriate steering signal for the tap T i  respective to a given controller C i  is determined. In the present embodiment, this step is performed by adjuster  212 . Continuing with the above example being discussed with reference to  FIG. 5 , the result  404   a  from each integrator  208  is then passed to its respective adjuster  212 . As shown in the example of  FIG. 5 , the result  404   a  from each integrator  208  was “0”, and this value is passed to adjuster  212 . 
     In the present embodiments, adjuster  212  includes digital signal processing circuitry that is operable to make the determination of whether and how to steer the tap T based on the result  404   a  passed from its respective integrator  208 . Adjuster  212  determines from the received “0” input that no steering of a tap T is required and the method advances to step  360 , wherein no adjustment is made to the steering signal applied to the respective tap T. 
     If adjuster  212  had received a positive or negative input from the result  404   a , then an appropriate adjustment to the tap steering signal would be determined and the method would have advanced to step  360  where the appropriate adjustment of the steering signal is applied to the respective tap T. 
     Continuing with the example being discussed in conjunction with  FIG. 5 , as it was determined at step  340  that no adjustment to the steering signal was required, and as feed forward amplifier  20  has just been activated, adjuster  212  determines that the tap T for its respective controller C should remain in its nominal position. Each adjuster  212  then outputs a corresponding tap steering signal, indicated on  FIG. 5  as signals  408   a   1  and  408   a   2 . The exact format of tap steering signals  408  can be generated using known means and circuitry and need only correspond with the format required to control the specific type of gain and phase adjusters used within amplifier portion  24 . 
     Tap steering signals  408   a  are then presented to their respective summer  216 , which sums the tap steering signal  408   a  with an attenuated version AW of the Walsh code W. This attenuated Walsh code is indicated on  FIG. 5  as items AW 1  and AW 2  and is the tracer signal to be injected in the signal paths of amplifier portion  24  for the next iteration of the control method. It will be apparent to those of skill in the art that the factors A for each attenuator  220  can differ from each other. Attenuated Walsh codes AW are attenuated by factors A to a level, appropriate for the specific GPA employed, so they act as a “dither” modulated on top of its tap steering signal  408   a  and that operation of the gain and phase GPA is not impeded by the dither. 
     Attenuated Walsh codes AW are produced by attenuators  220 , which simply receive the output of their respective Walsh code generator  204  and generate and output an attenuated version thereof to their respective summers  216 . Thus, each tap steering signal  408   a  and respective attenuated Walsh code AW are combined by their respective summer  216 , to create a dithered tap steering signal, indicated on  FIG. 5  as items  412   a   1  and  412   a   2 . At step  360 , the dithered tap steering signals  412   a   1 ,  412   a   2  are then presented to their respective taps T 1 , T 2  of GPA 1  and the method then returns to step  300 , where another iteration of the method begins. 
     As mentioned above, the method shown in  FIG. 3  operates simultaneously for detector D 2  and controllers C 3  and C 4  in the same manner as that described above for detector D 1  and controllers C 1  and C 2 . Thus, steering adjustments can be effected at each tap T at the same time. 
     An example of a second iteration through the method of  FIG. 3  will now be discussed with reference to  FIG. 6 . It is assumed that, prior to this iteration an input signal is being input along input signal path  40 .  FIG. 6  again shows detector D 1  and controllers C 1  and C 2 . This iteration commences with step  300  again being performed by detector D 1 . As there is now an input signal along input signal path  40 , detector D 1  now detects the tracer signal (dither) that has been applied to at least one of the gain and phase adjusters and reflects this detection in detector-output waveform  400   b . For purposes of explaining the present embodiment, it will be assumed that detector-output waveform  400   b  is {−3, −1, 0, 2, −3, 0, −1, 1} and waveform  400   b  is input to multipliers  200   1  and  200   2 . 
     Referring again to  FIG. 3 , the method then advances to step  320  where the tap measurement for the tap T i  respective to the controller C i  is extracted from the signal detected at step  300 . In the present example discussed in conjunction with  FIG. 6 , this signal is extracted from detector-output waveform  400   b  using multiplier  200   i  and integrator  208   i  of each controller C i . First, multiplier  200  multiplies the Walsh code output from Walsh code generator  204  with the detector-output waveform  400   b . The product waveform is then presented to integrator  208 , which sums each pulse in the waveform over the number chips in the Walsh code. The results from each integrator  208   1 ,  208   2  are represented on  FIG. 6  as items  404   b   1  and  404   b   2 , respectively. 
     Specifically, for controller C 1 , since the detector-output  400   b ={−3, −1, 0, 2, −3, 0, −1, 1}, and since the output of Walsh-code generator  204   1  W 1 ={1, −1, −1, 1, −1, 1, 1, −1}, then the output of multiplier  200   1  can be represented as {−3, −1, 0, 2, −3, 0, −1, 1}×{1, −1, −1, 1, −1, 1, 1, −1}=(−3, 1, 0, 2, 3, 0, −1, −1). The result for integrator  208   1  can be represented as  404   b   1 =(−3, 1, 0 2, 3, 0, −1, −1)=1. Similarly, for controller C 2 ,  400   b ={−3, −1, 0, 2, −3, 0, −1, 1} and since the output of Walsh-code generator  204   2  W 2 ={1, −1, 1, −1, 1, −1, 1, −1}, then the output of multiplier  200   2  can be represented as {−3, −1, 0, 2, −3, 0, −1, 1}×{1, −1, 1, −1, 1, −1, 1, −1}=(−3, 1, 0, −2, −3, 0, −1, −1). The result for integrator  208   2  can be represented as  404   b   2 =(−3, 1, 0, −2, −3, 0, −1, )=−9. 
     The method then advances to step  340  where the appropriate steering signal for the tap T respective to a given controller C is determined. Continuing with the above example being discussed with reference to  FIG. 6 , the result  404   b  for each integrator  208  is then passed to its respective adjuster  212 . In this example, the result  404   b   1  produced by integrator  208   1  was “1” and this value is passed to adjuster  212   1 . The result  404   b   2  produced by integrator  208   2  was “−9”, and this value is passed to adjuster  212   2 . In each case, the sign of the integrator output determines which way the respective tap T is adjusted. 
     As previously discussed, adjusters  212  include digital signal processing circuitry which is operable to make the determination of whether to steer the tap T based on the result  404   b  passed from its respective integrator  208 . In the present embodiment, adjusters  212  are configured so that, if the received input from its respective integrator  208  does not equal “0”, then it is determined that steering of its respective tap T is required. Accordingly, in the example of  FIG. 6  adjusters  212   1  and  212   2  both determine that steering of the respective taps T 1 , T 2  is required. 
     For controller C 1 , adjuster  212   1  has received a “1”, and thereby determines that the tap steering signal  408   b   1  to tap T 1  should be increased and accordingly, the output tap steering signal  408   b   1  is increased by a preselected increment from the previous signal that was used during the previous iteration through the method of  FIG. 3 . For controller C 2 , adjuster  212   2  has received a “−9”, and thereby determines that the tap steering signal  408   b   2  to tap T 2  should be decreased and accordingly, the output tap steering signal  408   b   2  is decreased by a preselected increment from the previous signal that was used during the previous iteration through the method of  FIG. 3 . Tap steering signals  408   b  are then presented to their respective summer  216 , which sums the tap steering signal  408   a  with the respective attenuated Walsh code AW. Thus, each tap steering signal  408   a  and attenuated Walsh code AW are summed together by their respective summer  216 , to create a dithered tap steering signal, indicated on  FIG. 6  as items  412   b   1  and  412   b   2 . The dithered tap steering signals  412   b  are then presented to their respective taps T of their respective GPA at step  360 . 
     Iterations through the method of  FIG. 3  repeat continuously for each controller C, increasing or decreasing each tap output signal  412  until an optimum level for a respective tap T is reached, at which point the respective controller C simply maintains the tap output signal  412  at its current level (i.e.—the result from integrator  208  of the product from multiplier  200  of waveform  400  and Walsh code W is “0”) until, during a subsequent iteration through the method of  FIG. 3 , further steering of the respective tap T is required. 
     While the embodiments discussed herein are directed to specific implementations of the invention, it will be understood that combinations, sub-sets and variations of the embodiments are within the scope of the invention. For example, it will now be apparent to those of skill in the art that amplifier portion  24  is a substantially known configuration for one type of amplifier portion of a feed forward amplifier, yet other configurations of amplifier portion  24  are within the scope of the invention. Other such configurations are discussed in a co-pending U.S. patent application Ser. No. 09/715,085, assigned to the assignee of the present invention, the contents of which are incorporated herein by reference. In particular, this application teaches a feed forward amplifier with a single pilot tone generator receiver, which is also suitable for incorporation into the present invention. A general discussion of feed forward amplifiers instructive to those of skill in the art for the design of amplifier portions is discussed in U.S. Pat. No. 3,471,798, the contents of which are also incorporated herein by reference. 
     As will also be apparent to those of skill in the art, feed forward amplifiers can include more than two gain and phase adjusters. In such a case, a detector-controller circuit can be employed for each gain and phase adjuster and a separate orthogonal tracer signal employed for each tap T. 
     Further, while the embodiments discussed herein refer specifically to FFAs having a pilot tone, it is to be understood that the present invention is also applicable to FFAs that do not use pilot tone, but use some other method, for example such as measuring intermodulation energy at detector D 2 . 
     While the embodiments discussed herein refer to gain and phase adjusters having gain and phase taps T, it is to be understood that the present invention is not so limited and can be applied to other types of adjusters, such as phase and gain adjusters having in phase ‘T’ and quadrature “Q” taps. Furthermore, while the embodiments discussed herein refer to controlling gain and phase adjustments in FFAs, it is to be understood that the apparatus and method discussed herein can be modified for use with any appropriate circuit where adaptive control is used, such as feed forward circuits, etc. 
     It is also to be understood that while the embodiments discussed herein refer to Walsh codes, any type of orthogonal tracer-signal, such as suitable length pseudo noise sequences or the like can be used, with appropriate modifications to other aspects of the remainder of the circuit. Additionally, while the number of chips of the Walsh codes used in the exemplary embodiments discussed herein corresponds to the period of the pulse wave-form of the detector-output, it will be understood that these periods need not correspond at all. In general, it is to be understood that any means or method for extracting a particular tap measurement from a detector-output can be used, such as using frequency division multiplexing. 
     While presently less preferred due to increased complexity, it is contemplated that the magnitude of the output of integrator  208  could also be used to provide further information to determine the amount by which each tap T is to be steered, in addition to using the polarity of the integrated signal to determine the direction the tap T should be steered. In such a case, instead of adjusting the amount by a preselected increment, a variable increment can be selected depending upon the magnitude of the output. 
     It is also contemplated that the size of the increment can vary, in a preselected manner, between start up of the adaptive circuit and normal operation of the adaptive circuit. For example, at start up and for a given number of iterations, amplifier  20  of  FIG. 1  can employ an increment/decrement size of 5 units, followed by an increment/decrement size of 3 units for another given number of iterations, then followed by an increment/decrement size of 2 units for another given number of iterations, after which an increment/decrement size of 1 unit is employed. This should allow faster convergence of the amplifier at start up. 
     The present invention provides a novel feed forward amplifier that includes a method and apparatus for steering the gain and phase adjustment such that each tap within the gain and phase adjusters is adjusted at substantially the same time to converge towards an optimum operating setting. Convergence towards the optimum settings are therefore obtained substantially faster and/or more accurately than prior art feed forward amplifiers. Each tap can have a tracer signal, which is orthogonal to other tracer signals, applied to the signal paths through the amplifier. The respective tap measurement is extracted and employed by each tap controller to appropriately alter the respective tap steering signal. 
     The above-described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto.