Circuit and method for detecting ac voltage pulses

Abstract

A detection circuit and method for detecting AC voltage pulses at a defined frequency relate to first transforming an input signal to a low-frequency signal by multiplying the input signal by a mixing frequency. This down-mixed signal can then be filtered and evaluated. The circuit is particularly suitable for identifying charge unit signals in the telephone network.

1 . A circuit for detecting AC voltage pulses at a defined frequency, comprising: 
 an analog/digital converter unit for converting an input signal to a sequence of sample values;    at least one mixing stage for multiplying the sequence of sample values by a mixing frequency signal, said mixing stage having a quadrature signal path and an in-phase signal path;    at least one filter stage for defining a permissible intermediate frequency band and for obtaining converted sample values by filtering the sequence of sample values having been multiplied by the mixing frequency signal; and    an evaluation unit for determining whether an AC voltage pulse is present by using the converted sample values, said evaluation unit squaring, adding and comparing the converted sample values in said quadrature signal path and in said in-phase signal path with a threshold value.    
   
   
       2 . The circuit according to  claim 1 , further comprising at least one decimation stage for reducing a signal rate by omitting sample values.  
   
   
       3 . The circuit according to  claim 2 , wherein: 
 in said quadrature signal path the sequence of sample values is multiplied by a sine signal at the mixing frequency signal; and    in said in-phase signal path the sequence of sample values is multiplied by a cosine signal at the mixing frequency signal.    
   
   
       4 . The circuit according to  claim 3 , wherein in said quadrature signal path, the sequence of sample values is multiplied by the sine signal by multiplying the sequence of sample values by a sequence 0, 1, 0, −1, 0, . . . .  
   
   
       5 . The circuit according to  claim 3 , wherein in said in-phase signal path, the sequence of sample values is multiplied by the cosine signal by multiplying the sequence of sample values by a sequence 1, 0, −1, 0, 1, . . . .  
   
   
       6 . The circuit according to  claim 1 , wherein the mixing frequency signal of said mixing stage has a frequency corresponding to the frequency of the AC voltage pulses that will be detected.  
   
   
       7 . The circuit according to  claim 1 , further comprising: 
 a first mixing stage defining said mixing stage, said first mixing stage for multiplying the sequence of sample values by a first mixing frequency signal having a frequency corresponding to a frequency of a first type of AC voltage pulses; and    a second mixing stage configured between said first mixing stage and said evaluation unit;    said second mixing stage for multiplying the sequence of sample values by a second mixing frequency signal having a frequency corresponding to a difference frequency formed by a difference between the frequency of the first type of AC voltage pulses and a frequency of a second type of AC voltage pulses.    
   
   
       8 . The circuit according to  claim 7 , further comprising: 
 a low-pass filter stage having a cut-off frequency above the difference frequency; said low-pass filter stage configured between said first mixing stage and said second mixing stage.    
   
   
       9 . The circuit according to  claim 1 , wherein the AC voltage pulse is a charge unit signal in a telephone network.  
   
   
       10 . A telephone portion, comprising: 
 an analog/digital converter unit for converting an input signal to a sequence of sample values;    at least one mixing stage coupled to receive the sequence of sample values and to multiply the sequence of sample values by a mixing frequency signal;    at least one filter stage coupled to filter the sequence of sample values multiplied by the mixing frequency signal to define a permissible intermediate frequency band and to provide converted sample values;    an evaluation unit coupled to receive the converted sample values to determine whether a charge unit signal is present; and    a speech path coupled to for performing audio signal processing, the charge unit signal being detected via said speech path.    
   
   
       11 . The telephone portion according to  claim 10 , wherein: 
 said analog/digital converter unit is configured in the speech path; and    the charge unit signals are digitized by said analog/digital converter unit.    
   
   
       12 . The telephone portion according to  claim 10 , further comprising at least one digital signal processor for implementing at least said mixing stage and said filter stage.  
   
   
       13 . A method for identifying different types of AC voltage pulses each having a defined frequency, the method which comprises: 
 digitizing an input signal to form a sequence of digitized sample values;    obtaining a sequence of converted sample values by converting the sequence of sample values using any desired sequence of steps including multiplying the sequence of sample values by predetermined mixing frequency signals and filtering the sequence of sample values to define a permissible intermediate frequency band; and    using the sequence of converted sample values to determine whether a specific type of AC voltage pulse is present by squaring, adding and comparing the sequence of converted sample values with a threshold value.    
   
   
       14 . The method according to  claim 13 , which further comprises, while performing the step of converting the sequence of sample values, reducing a signal rate by reducing a number of the sample values in the sequence of sample values.  
   
   
       15 . The method according to  claim 13 , wherein the step of multiplying the sequence of sample values by predetermined mixing frequency signals includes multiplying the sequence of sample values by a mixing frequency signal having a frequency corresponding to a frequency of the AC voltage pulses being identified.  
   
   
       16 . The method according to  claim 13 , wherein the step of multiplying the sequence of sample values by predetermined mixing frequency signals includes first multiplying the sequence of sample values by a first mixing frequency signal having a frequency corresponding to a frequency of a first type of AC voltage pulses, and subsequently multiplying the sequence of sample values by a second mixing frequency signal having a frequency corresponding to a difference between the frequency of the first type of AC voltage pulses and a frequency of a second type of AC voltage pulses.  
   
   
       17 . The method according to  claim 13 , wherein the AC voltage pulses are charge unit signals in a telephone network.  
   
   
       18 . A detection circuit, comprising: 
 an analog/digital converter to convert an input signal to a sequence of sampled values;    a mixing stage having a quadrature signal path and an in-phase signal path and multiplying said sequence of sampled values by a mixing frequency signal to provide of mixed sampled values;    a filter stage coupled to receive said mixed sampled values and to filter said mixed sampled values to converted sample values; and    an evaluation unit coupled to receive mixed sampled values, the evaluation unit including a circuit to square, and add said converted sample values and compare results with a threshold value to determine whether an AC voltage pulse is present.    
   
   
       19 . A telephone, comprising: 
 an analog/digital converter to convert an input signal in a speech path of the telephone to a sequence of sampled values;    a mixing stage to multiply said sequence of sampled values by a mixing frequency signal to provide mixed sampled values at an output of the mixing stage, the mixing frequency having a value determined by a frequency of a charge unit signal for the telephone;    a filter stage coupled to receive said mixed sampled values and filter said mixed sampled values to converted sampled values;    an evaluation unit coupled to receive said converted sample values and determine whether the charge unit signal is present.    
   
   
       20 . A method of processing an input signal to detect an AC pulse having a predetermined frequency, comprising: 
 digitizing the input signal to a sequence of sample values;    multiplying said sequence of sample values by a mixing frequency signal having a frequency determined by the frequency of the AC pulse to provide mixed sample values, using a mixing stage having a quadrature signal path and an in phase signal path;    filtering said mixed sample values to provide converted sample values; and    squaring, adding and comparing said converted sample values with a threshold value, and determining whether the AC voltage pulse is present.    
   
   
       21 . A circuit for detecting AC voltage pulses at a defined frequency, comprising: 
 an analog/digital converter unit for converting an input signal to a sequence of sample values;    at least one mixing stage for multiplying the sequence of sample values by a mixing frequency signal, said mixing stage has a quadrature signal path in which the sequence of sample values is multiplied by a sine signal at the mixing frequency; and said mixing stage has an in-phase signal path in which the sequence of sample values is multiplied by a cosine signal at the mixing frequency;    at least one filter stage for defining a permissible intermediate frequency band and for obtaining converted sample values by filtering the sequence of sample values having been multiplied by the mixing frequency signal;    an evaluation unit for determining whether an AC voltage pulse is present by using the converted sample values wherein said evaluation unit squares, adds and compares converted sample values in said quadrature signal path and in said in-phase signal path with a threshold value; and    at least one decimation stage for reducing a signal rate by omitting sample values.    
   
   
       22 . The circuit according to  claim 21 , wherein in said quadrature signal path, the sequence of sample values is multiplied by the sine signal by multiplying the sequence of sample values by a sequence 0, 1, 0, −1, 0, . . . .  
   
   
       23 . The circuit according to  claim 21  , wherein in said in-phase signal path, the sequence of sample values is multiplied by the cosine signal by multiplying the sequence of sample values by a sequence 1, 0, −1, 0, 1, . . . .  
   
   
       24 . The circuit according to  claim 21 , wherein the mixing frequency signal of said mixing stage has a frequency corresponding to the frequency of the AC voltage pulses that will be detected.  
   
   
       25 . The circuit according to  claim 21 , further comprising: 
 a first mixing stage defining said mixing stage, said first mixing stage for multiplying the sequence of sample values by a first mixing frequency signal having a frequency corresponding to a frequency of a first type of AC voltage pulses; and    a second mixing stage configured between said first mixing stage and said evaluation unit; said second mixing stage for multiplying the sequence of sample values by a second mixing frequency signal having a frequency corresponding to a difference frequency formed by a difference between the frequency of the first type of AC voltage pulses and a frequency of a second type of AC voltage pulses.    
   
   
       26 . The circuit according to  claim 25 , further comprising: 
 a low-pass filter stage having a cut-off frequency above the difference frequency; said low-pass filter stage configured between said first mixing stage and said second mixing stage.    
   
   
       27 . The circuit according to  claim 21 , wherein the AC voltage pulse is a charge unit signal in a telephone network.  
   
   
       28 . A telephone portion including a circuit for detecting charge unit signals at a defined frequency, the circuit comprising: 
 an analog/digital converter unit for converting an input signal to a sequence of sample values;    at least one mixing stage for multiplying the sequence of sample values by a mixing frequency signal;    at least one filter stage for defining a permissible intermediate frequency band and for obtaining converted sample values by filtering the sequence of sample values having been multiplied by the mixing signal;    an evaluation unit for determining whether a charge unit signal is present by using the converted sample values; and    a speech path via which audio signal processing is performed; the charge unit signals being detected via the speech path.    
   
   
       29 . The telephone portion according to  claim 28 , wherein: 
 said analog/digital converter unit is configured in the speech path; and    the charge unit signals are digitized by said analog/digital converter unit.    
   
   
       30 . The telephone portion according to  claim 29 , further comprising: 
 at least one digital signal processor for implementing at least said mixing stage and said filter stage.    
   
   
       31 . A method for identifying different types of AC voltage pulses each having a defined frequency, the method which comprises: 
 digitizing an input signal to form a sequence of digitized sample values;    obtaining a sequence of converted sample values by converting the sequence of sample values using any desired sequence of steps including multiplying the sequence of sample values by predetermined mixing frequency signals and filtering the sequence of sample values to define a permissible intermediate frequency band and which further comprises, while performing the step of converting the sequence of sample values, reducing a signal rate by reducing a number of the sample values in the sequence of sample values; and    using the sequence of converted sample values to determine whether a specific type of AC voltage pulse is present wherein the step of determining whether a specific type of AC voltage pulse is present includes squaring, adding and comparing the sequence of converted sample values with a threshold value.    
   
   
       32 . The method according to  claim 31 , wherein the step of multiplying the sequence of sample values by predetermined mixing frequency signals includes multiplying the sequence of sample values by a mixing frequency signal having a frequency corresponding to a frequency of the AC voltage pulses being identified.  
   
   
       33 . The method according to  claim 31 , wherein the step of multiplying the sequence of sample values by predetermined mixing frequency signals includes first multiplying the sequence of sample values by a first mixing frequency signal having a frequency corresponding to a frequency of a first type of AC voltage pulses, and subsequently multiplying the sequence of sample values by a second mixing frequency signal having a frequency corresponding to a difference between the frequency of the first type of AC voltage pulses and a frequency of a second type of AC voltage pulses.  
   
   
       34 . The method according to  claim 31 , wherein the AC voltage pulses are charge unit signals in a telephone network.