Spectral stitching method to increase instantaneous bandwidth in vector signal analyzers
Various embodiments are described of devices and associated methods for processing a signal using a plurality of vector signal analyzers (VSAs). An input signal may be split and provided to a plurality of VSAs, each of which may process a respective frequency band of the signal, where the respective frequency bands have regions of overlap. Each VSA may adjust the gain and phase of its respective signal such that continuity of phase and magnitude is preserved through the regions of overlap. The correction of gain and phase may be accomplished by a complex multiply with a complex calibration constant. A complex calibration constant may be determined for each VSA by comparing the gain and phase of one or more calibration tones generated with each region of overlap, as measured by each of the VSAs.
1. A method for processing a received signal, the method comprising:
summing a plurality of component signals to obtain a composite signal;
digitizing, prior to the summing, each of the plurality of component signals, each component signal comprising a respective frequency band of the received signal;
frequency-shifting the component signals, prior to the summing, such that the respective frequency band of each component signal has a respective region of overlap with the frequency band of at least one other of the component signals;
shaping a frequency response of the component signals, by a digital filter prior to the summing, wherein a shape of the digital filter is based on the regions of overlap, wherein the digital filter has a reduced gain in at least a portion of the regions of overlap to reduce artificial increases in magnitude in the sum of the component signals in the regions of overlap; and
wherein said digitizing, frequency-shifting, and shaping, are performed by a respective signal processing pathway for each component signal and wherein the component signals are phase-locked.
2. The method of claim 1 , further comprising:
adjusting the gain and phase of the component signals, prior to the summing, such that the sum of the component signals has a continuous frequency response over an aggregate frequency band comprising each of the frequency-shifted frequency bands.
3. The method of claim 1 , wherein the shaping is performed after the digitizing and before the frequency-shifting.
4. The method of claim 1 , wherein the digitizing comprises, for each component signal, shifting a center frequency of the respective frequency band to baseband; and
wherein the frequency-shifting comprises, for each component signal, frequency-shifting the component signal by a difference between the original center frequency of the respective frequency band and a center frequency of the received signal.
5. The method of claim 1 , further comprising interpolating the component signals after the digitizing and before the frequency-shifting.
6. The method of claim 1 , wherein the digital filter is a half-band filter.
7. The method of claim 1 , further comprising correcting a sampling delay of one or more of the component signals.
8. An apparatus, comprising:
a summing unit configured to sum outputs of a plurality of parallel signal processing pathways to obtain a composite signal;
a signal splitter configured to receive an analog signal, and output a plurality of copies of the analog signal;
the plurality of parallel signal processing pathways, wherein each of the parallel signal processing pathways is configured to receive from the signal splitter a respective copy of the analog signal, and to process a respective component signal of the analog signal, each component signal comprising a respective frequency band of the analog signal, wherein, to process the respective component signal to generate a respective output, each of the parallel signal processing pathways is configured to:
digitize, prior to the summation, the respective component signal;
frequency-shift, prior to the summation, the respective component signal such that the respective frequency band has a region of overlap with the frequency band of at least one other of the component signals; and
use a digital filter to filter the component signals, prior to the summation, wherein a shape of the digital filter is based on the regions of overlap, such that the sum of the component signals approximates an output that would be achieved using a single digitizer across an entire frequency band of the received analog signal.
9. The apparatus of claim 8 , wherein each of the parallel signal processing pathways is further configured to:
adjust gain and phase of a respective component signal, prior to the summation, such that the sum of the component signals has a continuous frequency response over an aggregate frequency band comprising each of the frequency-shifted frequency bands.
10. The apparatus of claim 8 , wherein each of the parallel signal processing pathways is configured to filter the component signals after digitizing the component signals and before frequency-shifting the component signals.
11. The apparatus of claim 8 , wherein to digitize the respective component signal, each of the parallel signal processing pathways is configured to shift a center frequency of the respective frequency band to baseband; and
wherein to frequency-shift the respective component signal each of the parallel signal processing pathways is configured to frequency-shift the component signal by a difference between the original center frequency of the respective frequency band and a center frequency of the received analog signal.
12. The apparatus of claim 8 , wherein each of the parallel signal processing pathways is further configured to:
interpolate the respective component signal after the digitization and before the frequency-shift.
13. The apparatus of claim 8 , wherein the digital filter is a half-band filter.
14. The apparatus of claim 8 , wherein one or more of the parallel signal processing pathways are further configured to:
correct a sampling delay of one or more of the component signals.
15. An apparatus, comprising:
a summing unit configured to sum outputs of a plurality of parallel signal processing pathways to obtain a composite signal;
a signal splitter configured to receive an analog signal, and output a plurality of copies of the analog signal;
the plurality of parallel signal processing pathways, wherein each of the parallel signal processing pathways configured to receive from the signal splitter a respective copy of the analog signal, and to process a respective component signal of the analog signal, each component signal comprising a respective frequency band of the analog signal, wherein, to process the respective component signal to generate a respective output, each of the parallel signal processing pathways is configured to:
digitize, prior to the summation, the respective component signal;
frequency-shift, prior to the summation, the respective component signal such that the respective frequency band has a region of overlap with the frequency band of at least one other of the component signals; and
use a digital filter to filter the component signals, prior to the summation, wherein a shape of the digital filter is based on the regions of overlap, and wherein the digital filter has a reduced gain in at least a portion of the regions of overlap to reduce artificial increases in magnitude in the sum of the component signals in the regions of overlap.
16. The apparatus of claim 15 , wherein each of the parallel signal processing pathways is further configured to:
adjust the gain and phase of a respective component signal, prior to the summation, such that the sum of the component signals has a continuous frequency response over an aggregate frequency band comprising each of the frequency-shifted frequency bands.
17. The apparatus of claim 15 , wherein each of the parallel signal processing pathways is configured to filter the component signals after digitizing the component signals and before frequency-shifting the component signals.
18. The apparatus of claim 15 , wherein to digitize the respective component signal, each of the parallel signal processing pathways is configured to shift a center frequency of the respective frequency band to baseband; and
wherein to frequency-shift the respective component signal each of the parallel signal processing pathways is configured to frequency-shift the component signal by a difference between the original center frequency of the respective frequency band and a center frequency of the received analog signal.
19. The apparatus of claim 15 , wherein each of the parallel signal processing pathways is further configured to:
interpolate the respective component signal after the digitization and before the frequency-shift.
20. The apparatus of claim 15 , wherein the digital filter is a half-band filter.