The goal of ELASTx is to enable monolithic, high power added efficiency (PAE), high linearity, millimeter-wave, silicon-based transmitter integrated circuits for next-generation military microsystems in areas such as radar, guidance and high data rate communications. DARPA envisions this goal will be achieved by investigating and developing complex, silicon-enabled RF, analog and mixed-signal circuit design techniques.
Low breakdown voltages of silicon-based devices have historically limited their applicability in power amplifiers (PAs). Instead, devices based on III-V compound semiconductor materials (e.g., GaAs, GaN and InP) have been used. Meanwhile, since many Department of Defense (DoD) applications of interest require high linearity for transmission of advanced waveforms, PA development consequently focused on linear amplifier classes (e.g., Class A and AB) at the expense of efficiency, which in turn limits the battery lifetime of mobile platforms. Amplifier efficiency can be significantly improved through the use of switching type amplifier classes (e.g. Class E and F), but amplifier linearity, measured, for example, in terms of error vector magnitude (EVM) and adjacent channel power ratio (ACPR), becomes severely degraded. Through the use of complex, silicon-enabled linearization architectures, the degraded linearity can be recovered, realizing a simultaneously high efficiency and high linearity RF transmitter. Through ELASTx, DARPA will develop novel approaches that enable a revolutionary increase in the PA efficiency while recovering linearity through integrated linearization architectures. The program demonstration will be a monolithic Watt-level silicon-based transmitter with an unprecedented 65% PAE and low EVM and ACPR for 64 QAM waveforms. The program is structured over three phases with demonstrations in increasingly aggressive goals for bandwidth and operating frequency: 3.5 GHz at 45 GHz, 5 GHz at 94 GHz, and 8 GHz at 138 GHz.
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