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Ultra high-speed data conversion offers many challenges to the system designer. Working with GHz analog signals is often referred to as a 'black art', so even experienced circuit designers are often hesitant when presented with such a challenge. This is truly a mixed signal environment in which all the sub circuits have to be considered carefully to allow the analog to digital converter (ADC) to deliver the optimum dynamic performance. Typical questions system designers might ask themselves are; Do I have adequate RF knowledge? Do I need to become familiar with smith chart theory again and get the charts out of the bottom drawer? What kinds of amplifiers exist with GHz bandwidth and low distortion over that entire bandwidth? How will I generate a clock signal for a GSPS converter? How can I possibility capture and process data at gigabits per second? Is my lab adequately equipped to use and evaluate such technology?
This article will explore various aspects of such designs, touching on input signal conditioning, clock generation, signal routing and data capture, and in doing so will answer the above questions. The good news is that reference designs are available that make the design of such sampling systems manageable, even without a strong RF or FPGA design background.
Gigasample converters are used in a wide variety of applications; precise measurement equipment (digital oscilloscopes, mass spectrometers, LIDAR modules), communications (point to point wireless links, wideband RADAR, satellite receivers) and scientific systems (particle detection, radio telescopes), to name a few. The architecture of these systems share common features. System performance is mostly dominated by ADC sampling speed and analog input bandwidth, and a high performance FPGA or ASIC is required for data capture. Digital oscilloscope performance is directly related to the ADC sampling rate in the analog front end. High sampling frequencies allow fast signals to be captured, displayed and analysed. ADC sampling frequency and bandwidth directly dictate the performance of wideband RADAR systems, satellite receivers and radio telescopes. The higher the conversion speed, the greater the instantaneous analog bandwidth that can be sampled.
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