Digital detector of an analog signal

Abstract

A circuit combination of integrated circuit (IC) digital devices for detecting an analog signal of a selected frequency and amplitude is disclosed. The circuit combination is a special-purpose digital filter of a predetermined bandwidth determined by the sample time T S duration and the low F L and high F H frequencies of the passable analog signal frequency having a carrier frequency F A . The analog signal is initially tested for minimal amplitude and converted to a digital signal by a conventional comparator circuit. The pulses of the digital signal are counted over the sample time T S and compared to the passable bandwidth: if the analog signal frequency F A .[. (F L ≦ F A ≦ F H ).]. is within the bandpass, .Iadd.F L ≦ F A < F H , .Iaddend. i.e., passable, a first binary signal is produced; alternatively, if the analog signal frequency F A .[. (F L > F A ≧ F H ).]. is without the bandpass, .Iadd.F L > F A ≧ F H , .Iaddend. i.e., not passable, a second binary signal is produced. Sample times continue throughout the detection-comparing operation to ensure a continuous filtering process.

What is claimed is: 
     
       1. A digital detector of an analog signal, comprising: means receiving an input analog signal of a frequency F A  for generating a digital signal of a frequency F A  therefrom;   counting means coupled to said digital signal for counting the number of pulses N A  thereof during a preset sample time T S  and generating a decode True signal if the counted number of pulses is equal to or greater than a preset low N L  number of pulses and generating a decode False signal if the counted number of pulses is .Iadd.equal to or .Iaddend.greater than a preset high N H  number of pulses for defining a preset bandwidth .[.N L  ≦ N A  ≦ N H  .]. .Iadd.N L  ≦ N A  < N H  .Iaddend.;   an output flip-flop for generating as the alternative output signals an output True signal or an output False signal indicating that said counting means has counted a number of pulses N A  of said digital signal that is within or without, respectively, said preset bandwidth;   a decoder flip-flop responsively coupled to said decode True signal and said decode False signal for storing a decoder True signal or a decoder False signal;   means gating the decoder True signal or the decoder False signal from said decoder flip-flop into said output flip-flop for storing and generating an output False signal or an output True signal, respectively, on a detector output line therefrom.   
     
     
       2. A digital detector of an analog signal, comprising: means receiving an input analog signal of a frequency F A  for generating a digital signal comprising a series of short duration pulses of a frequency F A , one pulse for every cycle of said input analog signal;   sample time base generator means coupled to said digital signal for generating, when effected by a first pulse of said digital signal, a sample time signal comprising a first sample time pulse and after the sample time T S  a second sample time pulse;   counting means coupled to said digital signal for counting the number of pulses N A  thereof during said sample time T S  and generating a decode True signal if the counted number of pulses is equal to .Iadd.or greater than .Iaddend.a preset low N L  count and generating a decode False signal if the counted number of pulses is .Iadd.equal to or .Iaddend.greater than a preset high N H  count for defining a preset bandwidth .[.N L  ≦ N A  ≦ N H  .]. .Iadd.N L  ≦ N A  < N H .Iaddend. ;   means coupling said sample time signal to said counting means for resetting said counting means to a zero count upon receipt of said first sample time pulse;   output memory means for generating as the alternative output signals an output True signal or an output False signal indicating that said counting means has counted a number of pulses of said digital signal that is within or without, respectively, said preset bandwidth;   decoder memory means coupled to said decode True signal and said decode False signal for coupling a decoder True signal or a decoder False signal to said output memory means;   means coupling said second sample time pulse to said output memory means for gating the decoder True signal or the decoder False signal from said decoder memory means into said output memory means and coupling an output True signal or an output False signal, respectively, therefrom on a detector output line.   
     
     
       3. The digital detector of claim 2 further including: gating means coupled to said detector output line and said sample time base generator means for generating a new sample time signal when affected by an output False signal. .Iadd. 4. A bandpass digital filter, comprising:   means for receiving an input signal of a frequency F A  ;   means responsively coupled to said receiving means for counting the number of pulses N A  of said input signal during a sample time T S  ;   means responsively coupled to said counting means for generating a first signal if the counted number of pulses N A  is equal to or greater than a low N L  number of pulses and for generating a second signal if the counted number of pulses N A  is equal to or greater than a high N H  number of pulses for defining a bandpass N L  ≦ N A  < N H  ;   means responsively coupled to said bandpass defining means for generating a within bandpass output signal only when said first signal but not said second signal was coupled thereto. .Iaddend..Iadd. 5. A bandpass digital filter, comprising:   means for generating a sample time signal of a duration T S  ;   means for receiving an input signal of a frequency F A  ;   means responsively coupled to said sample time signal generating means and said input signal receiving means for counting the number of pulses N A  of said input signal during said sample time T S  ;   means responsively coupled to said counting means for generating a first signal when the counted number of pulses N A  is equal to a low N L  number of pulses and a second signal when the counted number of pulses N A  is equal to a high N H  number of pulses for defining a bandpass N L  ≦ N A  < N H  ;   means responsively coupled to said bandpass defining means for generating a within bandpass output signal only if said first signal but not said second signal was coupled thereto. .Iaddend..Iadd. 6. A bandpass digital filter, comprising:   sample timing means for generating successive sample timing pulses, successive ones of which define successive sample times of a fixed duration T S  ;   input means for receiving an input signal of a frequency F A  ;   counting means responsively coupled to said sample timing means and said input means for counting the number of pulses N A  of an input signal during each of the successive ones of said sample times T S  ;   detector means responsively coupled to said counting means for generating a lower band edge detector signal when the counted number of pulses N A  is equal to a preset low N L  number of pulses and an upper band edge detector signal when the counted number of pulses N A  is equal to a preset high N H  number of pulses for defining a preset bandpass N L  ≦ N A  < N H  ;   output signal means responsively coupled to said detector means for generating a within bandpass signal only when said lower band edge detector signal but not said upper band edge detector signal is coupled thereto during any one of said successive sample times T S . .Iaddend..Iadd. 7. The bandpass filter of claim 6 wherein said output signal means includes a memory means;   means coupling said sample timing means to said memory means for setting said memory means into an initial False state at the beginning of each one of said successive sample times T S . .Iaddend..Iadd. 8. The bandpass filter of claim 7 wherein said output signal means includes means for coupling said lower band edge detector signal to said memory means for setting said memory means into a True state from said initial False state. .Iaddend..Iadd. 9. The bandpass filter of claim 8 wherein said output signal means includes means coupling said upper band edge detector signal to said memory means for setting said memory means back into said initial False state from said True state. .Iaddend..Iadd. 10. A bandpass digital filter, comprising:   means for generating successive sample time signals that define successive sample times that are each of a fixed duration T S  ;   means for receiving an input signal of a frequency F A  ;   means responsively coupled to said successive sample time signal generating means and said input signal receiving means for counting the number of pulses N A  of said input signal during each one of said successive sample times;   means responsively coupled to said counting means for generating a first signal when during a first one of said successive sample times the counted number of pulses N A  is equal to a low N L  number of pulses, i.e., N L  = N A , and for generating a second signal when during said first one of said successive sample times the counted number of pulses N A  is equal to a high N H  number of pulses, i.e., N A  = N H , said first and second signals defining a bandpass width N L  ≦ N A  < N H  ;   means responsively coupled to said bandpass width defining means for generating a within bandpass output signal during a second one of said successive sample times next following said first one of said successive sample times only when said first signal but not said second signal was coupled thereto during said first one of said successive sample times. .Iaddend.