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Frequency-domain multiplexing has been used for reading out ∼1000 detectors on the APEX-SZ and South Pole Telescope receiver for half a decade and produced many high-impact science papers. A new digital FPGA-based backend reduces the power consumption and system-size by an order of magnitude. This Digital Frequency-domain Multiplexer (DfMUX) was operated successfully in a space-like environment during the stratospheric balloon test-flight of the EBEX polarimeter, saw first light on the POLARBEAR experiment in 2010, and will be deployed for the South Pole Telescope polarimeter and ASTE sub-mm continuum camera. We are presently developing a new generation DfMUX targeting a factor 5 lower power consumption and robustness for satellite platforms. The system will incorporate new technology for identifying and correcting radiation induced errors in the FPGA logic, higher bandwidth to accommodate a multiplexing factor of 64, and Digital Active Nulling (DAN) feedback. DAN linearizes the SQUID system response while dramatically reducing its input impedance. [ABSTRACT FROM AUTHOR]