Spectral Stitching Method to Increase Instantaneous Bandwidth in Vector Signal Generators

An apparatus for processing a digital signal, the apparatus comprising:

• a processing element comprising a plurality of parallel processing paths, wherein the digital signal processor is configured to provide to each of the parallel processing paths a respective component signal comprising a copy of at least a respective frequency band of the digital signal, each respective frequency band having a respective center frequency and having a respective region of overlap with at least one other respective frequency band, wherein the combination of the respective frequency bands comprises an aggregate frequency band having an aggregate center frequency, wherein the respective center frequency of each respective frequency band has a respective frequency offset from the aggregate center frequency, and wherein each of the parallel processing paths is configured to:
• frequency-shift at least the respective frequency band of the respective component signal such that the respective center frequency is shifted to baseband;
• filter at least the respective frequency band of the respective component signal, wherein said filtering of the respective component signals is configured to cause a sum of the component signals to have a unity frequency response within each region of overlap;
• and
• adjust gain and phase of at least the respective frequency band of the respective component signal, wherein said adjusting gain and phase of the respective component signals is configured to cause the sum of the component signals to have a continuous frequency response over the aggregate frequency band;
• a plurality of output ports, each configured to provide to a respective vector signal generator (VSG) an output of one of the plurality of parallel processing paths;
• a plurality of input ports, each of the input ports configured to receive from a respective VSG a respective analog signal comprising an analog version of the output of the respective one of the plurality of output ports;
• and
• a signal combiner configured to combine the respective analog signals to obtain a composite signal.

A method for calibrating a signal processing system including at least a first vector signal generator (VSG) and a second VSG, the method comprising:

• providing to a first signal processing path comprising the first VSG a first digital component signal, the first digital component signal comprising a first frequency band within an aggregate frequency band of a digital input signal, the aggregate frequency band having an aggregate center frequency, and the first frequency band having a first center frequency at a first frequency offset from the aggregate center frequency;
• providing to a second signal processing path comprising the second VSG a second digital component signal, the second digital component signal comprising a second frequency band within the aggregate frequency band of the digital input signal, the second frequency band having a second center frequency at a second frequency offset from the aggregate center frequency, the second frequency band having a region of overlap with the first frequency band, the region of overlap containing a calibration tone, wherein the second VSG is phase-locked and time-synchronized with respect to the first VSG;
• frequency shifting each of the first and second component signals, such that the first center frequency and the second center frequency are each shifted to baseband;
• converting the first and second digital component signals to first and second analog component signals, respectively, using the first VSG and the second VSG;
• computing a complex calibration constant based on a magnitude ratio and a phase difference, wherein the magnitude ratio is determined by a magnitude of the calibration tone as output by the first VSG and a magnitude of the calibration tone as output by the second VSG, and wherein the phase difference is determined by a phase of the calibration tone as output by the first VSG and a phase of the calibration tone as output by the second VSG;
• storing the complex calibration constant in memory, wherein the complex calibration constant is useable to correct phase and gain mismatch between the first VSG and the second VSG.