This disclosure relates to test and measurement instruments, and in particular, to an acquisition apparatus of a test and measurement instrument having an arbitrary multiband overlay mixer apparatus and associated techniques for bandwidth multiplication.
The performance of test and measurement instruments, including digital oscilloscopes, is limited by the input bandwidth of the acquisition system. Conventional components for acquiring high frequency signals include sophisticated track and hold sampling circuitry, analog-to-digital conversion circuitry, high speed memory, and the like. However, traditional track and hold sampling and analog-to-digital circuitry require large investments of time and capital to effectively build and deploy.
Other approaches have involved the use of mixer technology in front of a digitizer platform to allow the system to have wider bandwidth, and a lower cost in development effort, compared to a standard digitizer platform architecture. In U.S. Patent Application Publication 2004/0128076 to Pupalaikis, et al., a real-time oscilloscope is disclosed with an increased usable bandwidth. The real-time oscilloscope splits the input signal into multiple split signals. One split signal is digitized. Simultaneously, the other split signals are frequency shifted to a baseband frequency range and digitized. The digitized frequency-shifted signals are frequency shifted to their original frequency range and then combined with the other digitized signals to create a representation of the input signal. By frequency shifting sub-bands of the input signal to be within the bandwidth of their respective digitizers, an input signal having a frequency range larger than the input bandwidth of a digitizer may be acquired using the lower bandwidth digitizers.
However, a need remains for a multi-band overlay apparatus and method that allows for arbitrary mixer local oscillator coefficients having an inverse matrix relationship to local oscillator coefficients used in the reconstruction of an input signal. In addition, it would be desirable to simultaneously digitize two wide band input signals using four digitizers of narrower bandwidth in a particular arrangement that provides for the use of arbitrary coefficients and an efficient reconstruction algorithm.