Abstract:
A signal treating apparatus for presenting an output signal representing an input signal over a signal range includes: (a) an input section receiving the input signal and presenting a first filtered signal limited to a first bandwidth at a first circuit locus; the input section presenting a second filtered signal limited to a second bandwidth at a second circuit locus; (b) an amplifying unit receiving the first filtered signal and presenting an increased gain signal at an amplifier output locus; (c) a detector coupled with the amplifier output locus and presenting third bandwidth-limited signal limited to a third bandwidth less than the first bandwidth at a third circuit locus; and (d) a combining section coupled with the second and third circuit loci and presenting a resulting signal related with the second filtered signal and the third filtered signal; said resultant signal being said output signal.

Description:
The invention was made with Government support under Contract Number FA8808-04-C-0022 awarded by the Air Force. The Government has certain rights in this invention. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure may be directed to signal treating apparatuses and methods, and especially to signal treating apparatuses and methods for treating a received signal to present a resulting signal having reduced signal deviations to produce a substantially accurate representation of the received signal. 
     BACKGROUND 
     A useful employment for the apparatus and method disclosed may be to provide a telemetry signal of received power which may be linear in decibels and continuous over a large dynamic range. An inherent difficulty of obtaining a linear telemetry signal over the input power dynamic range may arise from (1) the low Signal to Noise Ratio (SNR) at the low end of the dynamic range, and (2) saturation of an amplifier (such as by way of example and not by way of limitation, a Low Noise Amplifier (LNA)) at the high end of the dynamic range. Prior art approaches to overcoming this challenge may have used a processor which looks at the output power before and after a saturating stage of an LNA. The processor may make a crossover decision as to whether to use output power before or after the LNA. This prior art approach may be subject to alignment difficulties and requires a hysteresis band. 
     There may be a need for a method and apparatus for treating a received signal to present a resulting signal with improved signal accuracy. 
     SUMMARY 
     A signal treating apparatus for presenting an output signal representing an input signal over a signal range includes: (a) an input section receiving the input signal and presenting a first filtered signal limited to a first bandwidth at a first circuit locus; the input section presenting a second filtered signal limited to a second bandwidth at a second circuit locus; (b) an amplifying unit receiving the first filtered signal and presenting an increased gain signal at an amplifier output locus; (c) a detector coupled with the amplifier output locus and presenting third bandwidth-limited signal limited to a third bandwidth less than the first bandwidth at a third circuit locus; and (d) a combining section coupled with the second and third circuit loci and presenting a resulting signal related with the second filtered signal and the third filtered signal; said resultant signal being said output signal. 
     A method for treating a received signal to present a resulting signal representing the received signal with improved signal accuracy; the method including: (a) in no particular order: (1) effecting a first filtering of the received signal according to a first bandpass characteristic to present a first filtered signal at a first circuit locus; and (2) effecting a second filtering of the received signal according to a second bandpass characteristic to present a second filtered signal at a second circuit locus; (b) amplifying the first bandpass representation to present a high gain signal; (c) effecting a third bandwidth-limiting of the high gain signal to present a third bandwidth-limited signal at a third circuit locus; the third bandwidth-limited signal presenting a narrower band than the first bandpass representation; and (d) combining the second filtered signal with the third filtered signal to present the resulting signal. 
     It may therefore be a feature of the present disclosure to provide a method and apparatus for treating a received signal to present a resulting signal with improved signal accuracy. 
     Further features of the present disclosure may be apparent from the following specification and claims when considered in connection with the accompanying drawings, in which like elements may be labeled using like reference numerals in the various figures, illustrating the preferred embodiments of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of the apparatus of the present disclosure. 
         FIG. 2  is a graphic representation of selected signals associated with operation of the apparatus illustrated in  FIG. 1 . 
         FIG. 3  is a flow chart illustrating the method of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic diagram of the apparatus of the present disclosure. In  FIG. 1 , an apparatus  10  may include an input signal receiving section  12 , an amplifying unit  14 , a first detection portion  23 , a second detection portion  16  and a combining section  18 . 
     Amplifying unit  14  may have an input  32  and an output  36 . Combining unit  18  may include a logarithmic amplifier unit  40  and a summing unit  50 . Logarithmic amplifier unit  40  may have an input  42  and an output  44 . Summing unit  50  may have inputs  52 ,  56  and an output  54 . Output  44  may be coupled with input  52 . 
     Input signal receiving section  12  may include a first bandwidth limiting device  20  and a second bandwidth limiting device  22 . First bandwidth limiting device  20  may include a plurality of first bandpass filtering units  24   1 ,  24   2 ,  24   n . The indicator “n” is employed to signify that there can be any number of first bandpass filtering units in apparatus  10 . The inclusion of three first bandpass filtering units  24   1 ,  24   2 ,  24   n  in  FIG. 1  is illustrative only and does not constitute any limitation regarding the number of first bandpass filtering units that may be included in the apparatus of the present disclosure. 
     Second bandwidth limiting device  22  may include a plurality of second bandpass filtering units  26   1 ,  26   2 ,  26   m . The indicator “m” is employed to signify that there can be any number of second bandpass filtering units in apparatus  10 . The inclusion of three second bandpass filtering units  26   1 ,  24   2 ,  26   m  in  FIG. 1  is illustrative only and does not constitute any limitation regarding the number of second bandpass filtering units that may be included in the apparatus of the present disclosure. 
     First detection portion  23  may include optical detector units  28   1 ,  28   2 ,  28   m . Each respective optical detector unit  28   m  may be coupled with a respective second bandpass filtering unit  26   m  so that optical detector unit  28   1  may be coupled with second bandpass filtering unit  26   1 , optical detector unit  28   2  may be coupled with second bandpass filtering unit  26   2  and optical detector unit  28   m  may be coupled with second bandpass filtering unit  26   m . 
     First bandpass filtering units  24   1 ,  24   2 ,  24   n  may be commonly coupled with a circuit locus  27  and may be presented for selective inclusion in circuitry by a selecting switch  30 . Selecting switch  30  may be coupled with input  32  of amplifying unit  14 . Locus  27  may be coupled with an input locus  29 . Input signal receiving section  12  may also include an initial amplifying unit  34  coupled between loci  27 ,  29 . The optional nature of initial amplifying unit  34  may be indicated by employment of a dotted line format in representing initial amplifying unit  34 . 
     Second bandpass filtering units  26   1 ,  26   2 ,  26   m  may be commonly coupled with circuit locus  27  and may be presented for selective inclusion in circuitry by a selecting switch  38 . Selecting switch  38  may selectively couple a respective second bandpass filtering unit  26   m  with input  42  of logarithmic amplifier unit  40  via a respective optical detector unit  28   m . 
     Each respective first bandpass filtering unit  24   1 ,  24   2 ,  24   n  may effect filtering of signals to a respective frequency band so that first bandpass filtering unit  24   1  may filter signals to a frequency band centered on a frequency f 1 . First bandpass filtering unit  24   2  may filter signals to a frequency band centered on a frequency f 2 . First bandpass filtering unit  24   n  may filter signals to a frequency band centered on a frequency f n . 
     Each respective second bandpass filtering unit  26   1 ,  26   2 ,  26   m  may effect filtering of signals to a respective frequency band. It may be preferred that frequency bands selectable for filtering by second bandpass filtering units  26   1 ,  26   2 ,  26   m  may be substantially the same as frequency bands selectable for filtering by first bandpass filtering units  24   1 ,  24   2 ,  24   n . In such an arrangement, second bandpass filtering unit  26   1  may filter signals to a frequency band centered on frequency f 1 . Second bandpass filtering unit  26   2  may filter signals to a frequency band centered on frequency f 2 . Second bandpass filtering unit  26   m  may filter signals to a frequency band centered on frequency f n . Further in such an arrangement, n may be equal with m. 
     When received signals provided at input locus  29  may include optical signals, each respective second bandpass filtering unit  26   1 ,  26   2 ,  26   m  may be coupled with an optical detector unit  28   1 ,  28   2 ,  28   m  so that second bandpass filtering unit  26   m  may be coupled with an optical detector unit  28   1 , second bandpass filtering unit  26   2  may be coupled with an optical detector unit  28   2  and second bandpass filtering unit  26   m  may be coupled with an optical detector unit  28   m . 
     Selecting switches  30 ,  38  may be ganged together, as may be indicated by a dashed line  39 , to assure that similarly filtered signals may be presented at inputs  32 ,  42 . That is, to ensure that bandwidth BW 1  of signals provided from first bandwidth limiting device  20  may be substantially equal with bandwidth BW 2  of signals provided from second bandwidth limiting device  22 . Thus, when selecting switch  30  may be positioned for selecting first bandpass filtering unit  24   1 , selecting switch  38  may be positioned for selecting second bandpass filtering unit  26   2  and a frequency band centered on frequency f 2  may be presented at inputs  32 ,  42 . When selecting switch  30  may be positioned for selecting first bandpass filtering unit  24   2 , selecting switch  38  may be positioned for selecting second bandpass filtering unit  26   2  and a frequency band centered on frequency f 2  may be presented at inputs  32 ,  42 . When selecting switch  30  may be positioned for selecting first bandpass filtering unit  24   n , selecting switch  38  may be positioned for selecting second bandpass filtering unit  26   m  and a frequency band centered on frequency f n  (recall that n=m) may be presented at inputs  32 ,  42 . 
     Power into amplifying unit  14  may be expressed as:
 
 P   i   =S   i   +N   i   (1)
         Where P i  may be power present at input  32  of amplifier unit  14 ,
           S i  may be signal strength present at input  32 , and   N i  may be noise present at input  32 .   
               

     Power into input signal detection circuit  12  may be expressed as:
 
 P   ti   =S 1 det   +N 1 det   =f ( x )  (2)
         Where, P ti  may be total input power to input signal detection circuit  12 ,
           S1 det  may be signal strength detected at input  42 , and   N1 det  may be noise density detected at input  42 .   
               

     Second detection portion  16  may be coupled between output  36  of amplifying unit  14  and an input  56  of summing unit  50 . Second detection portion  16  may include a variable attenuator  60 , an optical detector unit  62 , a third bandwidth limiting device  64  and an electrical detector unit  66 . Variable attenuator  60  may be coupled with output  36  and with optical detector unit  62 . Third bandwidth limiting device  64  may be coupled between optical detector unit  62  and electrical detector unit  66 . Electrical detector unit  66  may be coupled with third bandwidth limiting device  64 , with variable attenuator  60  in a first order control loop. Electrical detector unit  66  may also be coupled with input  56  to summing unit  50 . Variable attenuator  60  may employ signals from electrical detector unit  66  to maintain signal levels at output  36  at a substantially constant level. Second detection portion  16  may be thus configured for treating a higher gain signal appearing at output  36  than may be presented at input  42  of logarithmic amplifier unit  40 . Further, when third bandwidth limiting device  64  may be configured to limit signals to a third bandwidth BW 3  that may be narrower than bandwidths to which signals may be limited by first bandwidth limiting device  20  (BW 1 ) or second bandwidth limiting device  22  (BW 2 ). Higher gain, lesser bandwidth treatment of signals may provide that signals provided from electrical detector unit  66  may exhibit a higher Signal-to-Noise Ratio (SNR) than may be exhibited by signals provided from bandwidth limiting devices  20 ,  22 . 
     When amplifier unit  14  may be in a saturated condition apparatus  10  may take advantage of amplifier average power saturation characteristics in a unique and subtle way to combine the input signals at input  42  with output signals at output  36  to obtain a substantially seamless continuous response signal with a simple circuit design. 
     Apparatus  10 , as illustrated in  FIG. 1 , may be configured for use with an optical communication system. One skilled in the art of signal handling apparatuses and methods may recognize that apparatus  10  may be employed with any communication system having an average power saturation amplifier. By way of example and not by way of limitation, apparatus  10  may provide benefit to a Transformational Satellite (TSAT) Communication System and to future communication programs by providing improved performance and simplicity of design. 
     As may be recognized by one skilled in the art of signal treatment, when signals received at input locus  29  may be entirely embodied in radio frequency (RF) signals, second detection portion  16  may be embodied in another feedback control configuration such as, by way of example and not by way of limitation, a phase locked loop. 
     Apparatus  10  may take particular advantage of the output Low Noise Amplifier (LNA) stage (embodied in amplifier unit  14  in  FIG. 1 ) always being saturated. Saturation may be a result of noise or a result of a combination of both signal and noise power. A mathematical analysis may provide insight into the operation of apparatus  10 .  FIG. 1  may illustrate a representative placement of optical filters, amplifiers and detection circuits that may be employed to determine the signal plus noise power at the saturating amplifier input and the signal power at the saturating amplifier output. As may be seen from  FIG. 1 , the output total power P TO  at output  36  may be substantially constant. P TO  may be expressed in the relationship:
 
 P   to   =S   o   +N   o =Constant  (3)
         Where P to  may be total output power from amplifier unit  14 ,
           S o  may be signal strength detected at output  36 , and   N o  may be noise density detected at output  36 .   
               

     Second detection portion  16  may employ a synchronous detection approach to detect an amplifier output signal received from output  36  by varying optical attenuator  60  using input signal power variation indicated at electrical detector unit  66  to hold the output signal power received by second detection portion  16  from output  36  substantially constant. The attenuator control function g(x) employed by variable attenuator  60  may be shown below in EQN (3) where x is the Signal to Noise Ratio (SNR): 
     
       
         
           
             
               
                 
                   Attenuation 
                   = 
                   
                     
                       1 
                       
                         g 
                         ⁡ 
                         
                           ( 
                           x 
                           ) 
                         
                       
                     
                     = 
                     
                       
                         N 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           2 
                           det 
                         
                       
                       
                         N 
                         o 
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
         
         
           
             Where N2 det  may be noise detected by second detection portion  16 . 
           
         
       
    
     No may make up total noise into second detection portion  16 . N2 det  may make up the total noise at the input of optical detector unit  62 . For all practical purposes the SNR may be considered the same after the BW 1  filter (first bandwidth limiting device  20 ) and may be used to represent the input signal power to the LNA because N i  (noise into amplifier  14 ) is substantially a constant, as may be seen in EQN (5): 
     
       
         
           
             
               
                 
                   Signal 
                   = 
                   
                     x 
                     = 
                     
                       
                         
                           S 
                           i 
                         
                         
                           N 
                           i 
                         
                       
                       = 
                       
                         
                           
                             S 
                             o 
                           
                           
                             N 
                             o 
                           
                         
                         = 
                         
                           
                             S 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               2 
                               det 
                             
                           
                           
                             N 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               2 
                               det 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
         
         
           
             Where S2 det  may be signal strength detected by second detection portion  16  although S2 det  may be measured at optical detector unit  62 . 
           
         
       
    
     Using EQNs (3), (4) and (5) the control function for variable attenuator  60  may be found using EQN (6):
 
 P   to   =S   o   +N   o =Constant= N   o ( x+ 1)  (6)
 
     Both P to  and S2 det  may be substantially constants so g(x) may have the nonlinear relationship shown in EQN (7): 
     
       
         
           
             
               
                 
                   
                     g 
                     ⁡ 
                     
                       ( 
                       x 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         P 
                         to 
                       
                       
                         N 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           2 
                           det 
                         
                         ⁢ 
                         
                           ( 
                           
                             x 
                             + 
                             1 
                           
                           ) 
                         
                       
                     
                     = 
                     
                       
                         ( 
                         
                           
                             P 
                             to 
                           
                           
                             S 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               2 
                               det 
                             
                           
                         
                         ) 
                       
                       · 
                       
                         ( 
                         
                           x 
                           
                             x 
                             + 
                             1 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     Because two different band limiting filters may be used, noise into input signal detecting circuit  12  may be adjusted by the ratio of the two filter bandwidths BW 1 , BW 2 . The noise density, represented by nd, as shown in EQN (8) may be the same at each filter output: 
     
       
         
           
             
               
                 
                   
                     n 
                     d 
                   
                   = 
                   
                     
                       
                         N 
                         i 
                       
                       
                         BW 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                     
                     = 
                     
                       
                         
                           N 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             1 
                             det 
                           
                         
                         
                           BW 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                       = 
                       Constant 
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     EQN (8) may be rewritten as EQN (9): 
     
       
         
           
             
               
                 
                   
                     
                       N 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         1 
                         det 
                       
                     
                     = 
                     
                       α 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         N 
                         i 
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   where 
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     α 
                     = 
                     
                       ( 
                       
                         
                           BW 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                         
                           BW 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     The signal at input signal detection circuit  12  may be substantially the same as the input signal to amplifying unit  14  as shown in EQN (10):
 
S1 det =S i   (10)
 
     Using EQNs (2), (5), (9), and (10) the input detector transfer function f(x) may be calculated in EQN (11).
 
 P   ti   =S 1 det   +N 1 det   =f ( x )= S   i   +αN   i   =N   i =( x +α)  (11)
 
     The nonlinear input function f(x) (EQN(11)) and output detection circuit function g(x) (EQN(7)) may now be combined using EQN (12) to form a linear telemetry signal when α=1, as shown in EQN (13).
 
 h ( x )= f ( x )· g ( x )  (12)
 
     
       
         
           
             
               
                 
                   
                     h 
                     ⁡ 
                     
                       ( 
                       x 
                       ) 
                     
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             P 
                             to 
                           
                           · 
                           
                             N 
                             i 
                           
                         
                         
                           S 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             2 
                             det 
                           
                         
                       
                       ) 
                     
                     · 
                     
                       ( 
                       
                         
                           x 
                           + 
                           α 
                         
                         
                           x 
                           + 
                           1 
                         
                       
                       ) 
                     
                     · 
                     x 
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
     The first term in equation (13) may involve all constant values so h(x) may be simply a function proportional to the input signal over the entire dynamic range. The operation may be substantially seamless and nearly linear when alpha may be a value other than unity. 
     When EQN (12) may be converted to decibels by taking the logarithm such as, by way of example and not by way of limitation, by employing logarithmic amplifier unit  40 , the two input and output functions f(x) and g(x) may be added together rather than multiplied, which simplifies the circuit design as illustrated by way of example and not by way of limitation in  FIG. 1  using summing unit  50 . In  FIG. 1 , second detection portion  16  may not need a logarithmic amplifier because voltage from second detection portion  16  is already proportional to decibels. 
     Apparatus  10  may be an implementation simple in design but subtle in operation. The simple design may provide a high reliability approach to improving accuracy of reproducing a received signal over a wider amplitude and signal strength ranges than may have been achieved using prior art devices, and may not be as susceptible to amplifier and circuit variation as prior art signal treating apparatuses. 
       FIG. 2  is a graphic representation of selected signals associated with operation of the apparatus illustrated in  FIG. 1 . In  FIG. 2 , a graphic representation  80  may present a horizontal axis  82  indicating input signal strength in decibels (dB) and a vertical axis  84  indicating output signal strength in decibels (dB). 
     A signal response curve  86  may represent a signal appearing at input  52  of summing unit  50  ( FIG. 1 ). A signal response curve  88  may represent a signal appearing at input  56  of summing unit  50  ( FIG. 1 ). A signal response curve  86  may represent a signal appearing at input  52  of summing unit  50  ( FIG. 1 ). 
     Signal response curve  86  may be a signal from input signal detecting section  12 . Signal response curve  88  may be a signal from second detection portion  16  ( FIG. 1 ). When signal response curves  86 ,  88  may be added, as may be effected by summing unit  50  ( FIG. 1 ), a substantially linear signal response, such as signal response curve  90 , may result. 
       FIG. 3  is a flow chart illustrating the method of the present disclosure. In  FIG. 3 , a method  100  for treating a received signal to present a resulting signal representing the received signal with improved signal accuracy may begin at a START locus  102 . Method  100  may continue with effecting a first filtering of the received signal according to a first bandpass characteristic to present a first filtered signal at a first circuit locus, as may be indicated by a block  104 . 
     Method  100  may continue by, substantially simultaneously with the method step represented by block  104 , amplifying the received signal to present a high gain signal, as may be indicated by a block  106 . 
     Method  100  may continue with effecting a second filtering of the high gain signal according to a second bandpass characteristic to present a second filtered signal at a second circuit locus, as may be indicated by a block  108 . The second bandpass characteristic may pass a narrower band than the first bandpass characteristic. 
     Method  100  may continue with combining the first filtered signal with the second filtered signal to present the resulting signal, as may be indicated by a block  110 . 
     Method  100  may terminate at an END locus  112 . 
     It is to be understood that, while the detailed drawings and specific examples given may describe preferred embodiments of the disclosure, they are for the purpose of illustration only, that the apparatus and method of the disclosure may not be limited to the precise details and conditions disclosed and that various changes may be made therein without departing from the spirit of the disclosure which is defined by the following claims: