Frequency-Domain Multiplexed Readout of Transition-Edge SensorArrays with a Superconducting Quantum Interference Device

We demonstrate an eight-channel frequency-domain readout multiplexer for superconducting transition-edge sensors (TESs). Each sensor is biased with a sinusoidal voltage at a unique frequency. The sensor currents are summed and measured with a single superconducting quantum interference device (SQUID) array. The 100-element SQUID array is operated with shunt feedback electronics that have a slew rate of 1.2 x 107PHI 0/s at 1 MHz. The multiplexer readout noise is 6.5 pA/sqrt Hz, which is well below the expected sensor noise of 15 pA/sqrt Hz. We measure an upper limit on adjacent channel cross talk of 0.004, which meets our design requirements. The demodulated noise spectra of multiplexed TESs are white at frequencies down to 200 mHz.