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Sponsored Contributed Article Analog-to-digital converters are continuing to reach higher frequencies at which signals captured over the air can be directly digitized – eliminating microwave downconverters in the process. Total downconverter elimination may be inevitable – but it won’t occur soon. Will Direct-to-Digital Conversion Displace Microwave Converters? By Barry Manz for Mouser Electronics IMAGINE what life would be like without the ability to convert analog information to the digital domain. The world as we know it might be like the 1950s, with no smartphones, HDTV, computers, or smartwatches. The list of the things that either would not exist or would be hobbled without analog-to-digital conversion (ADC) would be enormous. Most of the items on that list require ADC at low frequencies (and with digital-to-analog conversion, “DAC”). In the higher microwave region of the electromagnetic spectrum, conversion is still elusive. The benefits of conversion at very high frequencies, presently impossible, are cause for significant research by industry, academia, and defense. A great potential benefit is the ability to eliminate microwave downconverters and a significant number of analog components. The task of ingesting and digitizing higher instantaneous bandwidths falls to ADCs, which already possess formidable function. On the face of it, converting analog waveforms to the digital domain is no more complex at high frequencies. Conversions at high sampling rates, resolution, and dynamic range have long been a fait accompli. It’s Complicated Moore’s Law doesn’t apply to converters; leaps forward in sampling rate (and thus bandwidth) are extremely difficult to achieve. The most potent devices reside in the labs of test equipment manufacturers, device vendors, and the military. Just how high a frequency achieved to date is not clear, and there’s good reason for holding state-of-the-art conversion secrets closely. Converters are key performance determinants for oscilloscopes, spectrum and signal analyzers, and virtually every defense electronic system that relies on the electromagnetic spectrum. Running a close second are FPGAs, such as Altera’s Stratix V GX, and more recently, general-purpose graphics processing units that process massive amounts of data resulting from high-frequency direct-to-digital conversion. A simplified example: an ADC sampling at 20 Gb/s, which makes its instantaneous bandwidth about 10 GHz when operated in the first Nyquist zone. Assuming that the device has an Effective Number of Bits (ENOB) of 10, and a dynamic range of 70dB, it would be possible for the ADC to directly ingest DC to 10GHz with excellent resolution and dynamic range, without interstitial microwave downconverters to reduce the frequency to one that the ADC can handle. The result would be a major reduction in hardware, complexity, size, weight, and cost, and a commensurate increase in speed and flexibility; critical in many defense applications. One such example is the truly frightening interaction between search-and-fire control radars and the radar warning receivers (RWRs) and jammers in fighter aircraft. In a typical scenario, a radar acquires the target (fighter jet). The target’s jamming radar must capture the signal, digitize it, and then retransmit it as a waveform that essentially confuses the sourcing radar within less than a second. In both the fighter’s RWR and Electronic Warfare systems, and in the adversary’s radar, the ADC is the initial component determining frequency, speed, and degree of fidelity in signal acquisition. High-speed signal processing, the next element in the chain, has the daunting task of processing and transforming it into waveforms that can confuse the adversarial radar. The DAC must reconvert data from digital to analog, after which it is retransmitted at or near the original frequency. If the ADC Figure 1. A 10 GHz radio signal is picked up by the receive antenna. The microwave downconverter reduces the frequency to one that the system is able to process. The ADC converts it to 1s and 0s. As a digital signal, it is now possible to perform many functions that are not as easily done in analog format. But if the ADC can directly ingest the original 10 GHz analog signal, you eliminate the need for a big and expensive microwave downconverter. 10 Electronic Engineering Times Europe October 2014 www.electronics-eetimes.com


EETE OCT 2014
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