Patent Publication Number: US-8989253-B1

Title: Reconditioning equalizer filter for non-constant envelope signals

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation of copending, commonly-assigned U.S. patent application Ser. No. 14/138,959, filed Dec. 23, 2013, now U.S. Pat. No. 8,787,438, which is a continuation of, and was copending with, commonly-assigned U.S. patent application Ser. No. 11/603,679, filed Nov. 24, 2006, now U.S. Pat. No. 8,619,847, each of which is hereby incorporated by reference herein in its respective entirety. 
    
    
     BACKGROUND OF INVENTION 
     The present invention relates to a reconditioning equalizer filter to boost the output power of a wireless or wireline transmitter. The reconditioning equalizer filter input could be a baseband, intermediate frequency (IF), or RF signal, and its output is the peak-reduced and smoothened baseband signal that can be up-converted to IF or RF. In any wireless/wireline communication system one of the critical sub-systems is the transmitter. This sub-system has a major contribution in cost, power consumption, and size of the system. The main reason is the requirement of communication transmitter for linear components. The higher the linearity, the higher the power consumption, cost and size. In order to minimize the cost, size and power consumption there is a need for techniques that overcome this problem. This invention conquers these challenges by using a simple and accurate reconditioning equalizer filter module used at the input to this sub-system. 
     SUMMARY OF INVENTION 
     According to the invention, a reconditioning equalizer filter, for use with any transmitter, uses a plurality of simple and accurate algorithms in conjunction with intelligent signal processing to improve signal handling of any wireless, optical, or wireline transmitter. By intelligent, it is meant that the algorithm has features of restoring the signal emission and quality requirements after applying the reconditioning equalizer filter. The reconditioning equalizer filter uses the transmitter sub-system input which could be a baseband, IF or RF signal, as its input, and reconditions and smoothens the signal before applying it to the transmitter sub-system. The conditioning and smoothening helps to boost the power handling of the transmitter sub-system or acts more linear. The inputs to the reconditioning equalizer filter should be within a limit that can be handled by the reconditioning equalizer filter. 
     In a particular embodiment, the reconditioning equalizer filter algorithm comprises a signal processing module. The signal processor performs the signal conditioning and smoothening. 
     The invention will be better understood by reference to the following detailed description in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall block diagram of the reconditioning equalizer filter. 
         FIG. 2  is the detail block diagram of the reconditioning equalizer filter. 
         FIG. 3  is the block diagram of peak reduction filter using clipping. 
         FIG. 4  is the block diagram of the peak reduction filter using phase rotation. 
     
    
    
     DESCRIPTION OF THE SPECIFIC EMBODIMENTS 
     In a first preferred embodiment of the invention, the reconditioning equalizer filter uses sub-harmonic sampling to convert an RF or IF signal to a digital baseband signal. In a second preferred embodiment, the baseband signal&#39;s amplitude is conditioned and smoothened using a reconditioning equalizer filter. In a third embodiment, the peak reduction filter uses clipping function. In a fourth embodiment, the peak reduction filter uses phase rotation. In a fifth embodiment, the output of the reconditioning equalizer filter is used as the new input to the transmit sub-system. In a sixth embodiment, both the low pass filter in the feedforward loop and the peak reduction filter are configurable. In a seventh embodiment, a feedforward loop is used to inject in-band signal to the main baseband signal. In an eighth embodiment, a configurable low pass filter is used in the feedforward loop to adjust the in-band signal injected into the main baseband signal. In a ninth embodiment, a controller is used to define the value of gain and delay adjustments as well as other control parameters for various functions of the reconditioning equalizer filter. 
     Referring to  FIG. 1 , a reconditioning equalizer filter diagram is illustrated. The reconditioning equalizer filter  200  receives its baseband input  100  and produces conditioned and smoothened output  300 . The reconditioning equalizer filter performs the following functions:
         1. Condition and smoothen the amplitude of the input signal  100  before applying it to transmitter sub-system.   2. Adjust the gain in the signal paths to keep the total gain from input to output of the reconditioning equalizer filter unity.       

       FIG. 2  illustrates the detailed block diagram of the reconditioning equalizer filter unit. The received main baseband signal  100  is applied to Peak Reduction Filter (PRF)  201  to produce signal  250 . The PRF  201  receives control signal  260  from controller  211  to adjust the peak reduction. The main baseband signal  100  is delayed by delay block  202  to produce delayed main baseband signal  251 . The delayed main baseband signal  251  is gain-adjusted by gain block  203  to produce delay- and gain-adjusted baseband signal  252 . The delay- and gain-adjusted baseband signal  252  is subtracted from peak-reduced baseband signal  250  in subtraction block  204  to produce baseband signal  253 . The amount of delay  262  and gain adjustment  263  are calculated by the correlation block  205  that uses main baseband signal  100  and signal  253  as its input. The correlation block  205  also receives a control signal  261  from controller block  211  to use to calculate the delay signal  262  and gain adjustment signal  263 . The baseband signal  253  is filtered by Low Pass Filter (LPF)  207  to adjust the amount out-of-band signal rejection and produce in-band baseband signal  254 . The in-band baseband signal  254  is gain-adjusted by gain block  208  to produced gain-adjusted in-band baseband signal  256 . The amount of gain adjustment  265  is provided by controller block  211 . The main baseband signal  100  is delay- and gain-adjusted by delay/gain block  206  to produce delay- and gain-adjusted main baseband signal  255 . The delay- and gain-adjusted main baseband signal  255  and the gain-adjusted in-band baseband signal  256  are summed in summation block  209  to produce modified main baseband signal  257 . The modified main baseband signal  257  is gain-adjusted by gain block  210  to produce conditioned and smoothened baseband signal  300 . The main baseband signal  100  and the modified baseband signal  300  are applied to controller  211  to provide the gain and delay parameters needed for the gain blocks and the correlation block. 
       FIG. 3  shows the detailed block diagram of the Peak Reduction Filter (PRF)  201 . The main baseband signal  100  is applied to block  700  to be converted to real In-phase (I)  403  and quadrature phase (Q)  404  signals. The “I”  403  and “Q”  404  signals are applied to block  701  to calculated the magnitude  401  of the main baseband signal. The magnitude of the main baseband signal is applied to block  702  to define the lookup table pointer  402  that is being used for the lookup table block  706 . The pointer  402  selects the in-phase multiplier factor  405  and quadrature multiplier factor  406 . The in-phase multiplier factor  405  and the main in-phase (I) signal  403  are applied to multiplier  703  to produce the modified main in-phase signal  407 . The quadrature multiplier factor  406  and the main quadrature signal (Q)  404  are applied to multiplier  704  to produce modified quadrature signal  408 . The modified in-phase signal  407  and quadrature signal  408  are applied to block  705  to produce the modified main complex baseband signal  250 . 
       FIG. 4  shows the detailed block diagram of the Peak Reduction Filter (PRF)  201 . The main baseband signal  100  is applied to block  700  to be converted to real In-phase (I)  403  and quadrature phase (Q)  404  signals. The “I”  403  and “Q”  404  signals are applied to block  701  to calculated the magnitude  401  of the main baseband signal. The magnitude of the main baseband signal is applied to block  702  to define the lookup table pointer  402  that is being used for the lookup table block  707 . The lookup table block provides in-phase and quadrature phase angles whose “COSINE”  409  and “SINE”  410  are used in multipliers  703  and  704 . The pointer  402  selects the in-phase “COSINE” component  409  and quadrature “SINE” component  410 . The in-phase “COSINE” component  409  and the main in-phase (I) signal  403  are applied to multiplier  703  to produce the modified main in-phase signal  411 . The quadrature “SINE” component  410  and the main quadrature signal (Q)  404  are applied to multiplier  704  to produce modified quadrature signal  412 . The modified in-phase signal  411  and quadrature signal  412  are applied to block  705  to produce the modified main complex baseband signal  250 L