Logical triggering in the frequency domain

Abstract

A frequency mask trigger capable of triggering based on a logical combination of two or more areas of a frequency mask transforms a frame of digital data representing an input signal into a frequency spectrum having a plurality of frequency bins, with each frequency bin having a power amplitude value. A frequency mask is defined having a plurality of reference power levels, one reference power level being associated with each frequency bin. Two or more areas of the frequency mask are defined, with each mask area corresponding to one or more of the frequency bins. A violation status is determined for each mask area by comparing all of the power amplitude values within each mask area to the associated reference power level. If any of the power amplitude values within the mask area violates the associated reference power level, then the entire mask area is deemed to be violated. A trigger signal is generated when a logical combination of the violation statuses of the mask areas is satisfied.

1 . A test and measurement instrument comprising:
 an input processor for receiving an input signal and producing a digital signal;   a trigger signal generator for generating a trigger signal based on a logical combination of the violation statuses of two or more areas of a frequency mask; and   an acquisition memory for storing a seamless block of digital data from the digital signal in response to the trigger signal.   
     
     
         2 . The test and measurement instrument as recited in  claim 1  wherein the trigger signal generator comprises:
 a time-to-frequency converter for converting a frame of digital data from the digital signal into a frequency spectrum having a plurality of frequency bins, with each frequency bin having a power amplitude value; 
 a comparator for comparing the plurality of power amplitude values to an associated plurality of reference power levels that define the frequency mask, and for generating a plurality of output signals, with each output signal indicating whether a particular power amplitude value violates the associated reference power level; and 
 a logic qualifier for determining the violation status of the two or more mask areas of the frequency mask by examining the output signals of the comparator that correspond to each mask area, and for generating the trigger signal based on a logical combination of the violation statuses of the two or more mask areas. 
 
     
     
         3 . The test and measurement instrument as recited in  claim 1  wherein the trigger signal generator comprises:
 a time-to-frequency converter for converting a frame of digital data from the digital signal into a frequency spectrum having a plurality of frequency bins, with each frequency bin having a power amplitude value; 
 a comparator for determining the violation status of the two or more mask areas by comparing those power amplitude values that correspond to the two or more areas of the frequency mask to associated reference power levels, and for generating a plurality of output signals, with each output signal indicating the violation status of one of the two or more mask areas; and 
 a logic qualifier for generating the trigger signal based on a logical combination of the output signals of the comparator. 
 
     
     
         4 . The test and measurement instrument as recited in  claim 2  wherein the trigger signal generator further comprises a windowing function for windowing the frame of digital data. 
     
     
         5 . The test and measurement instrument as recited in  claim 3  wherein the trigger signal generator further comprises a windowing function for windowing the frame of digital data. 
     
     
         6 . The test and measurement instrument as recited in  claim 1  wherein the input processor comprises:
 a mixer for mixing the input signal with a local oscillator signal to produce an intermediate frequency signal; 
 a bandpass filter for filtering the intermediate frequency signal to produce a filtered intermediate frequency signal; and 
 an analog-to-digital converter for digitizing the filtered intermediate frequency signal to produce the digital signal. 
 
     
     
         7 . The instrument as recited in  claim 6  wherein the input processor further comprises an image reject filter for filtering the input signal. 
     
     
         8 . The test and measurement instrument as recited in  claim 1  wherein the time-to-frequency converter comprises a time-to-frequency transform selected from the group consisting of a discrete Fourier transform, a discrete Hartley transform, and a chirp-Z transform. 
     
     
         9 . The test and measurement instrument as recited in  claim 1  wherein the time-to-frequency converter comprises a bank of parallel filters selected from the group consisting of finite impulse response filters and continuous time analog filters.