Augustus Smith

Frequency-domain multiplexed readout of transition-edge sensor arrays 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 1.2×107Φ0∕s at 1MHz. The multiplexer readout noise is 6.5pA∕Hz, which is well below the expected sensor noise of 15pA∕Hz. We measure an upper limit on adjacent channel crosstalk of 0.004, which meets our design requirements. The demodulated noise spectra of multiplexed TESs are white at frequencies down to 200mHz.

Frequency-domain multiplexing for large-scale bolometer arrays

We describe the development of a frequency-domain multiplexer (MUX) to read out arrays of superconducting transition-edge sensors (TES). Fabrication of large-format arrays of these sensors is becoming practical; however, reading out each sensor in the array is a major instrumental challenge that is possibly solved by frequency-domain multiplexing. Each sensor is AC biased at a different frequency, ranging from 380 kHz to 1 MHz. The sensor signal amplitude-modulates its respective AC bias frequency. An LC filter associated with each sensor suppresses Johnson noise from the other sensors. The signals are combined at a current summing node and measured by a single superconducting quantum interference device (SQUID). The individual signals from each sensor are then lock-in detected by room temperature electronics. Test chips with fully lithographed LC filters for up to 32 channels have been designed and fabricated. The capacitance and inductance values have been measured and are close to the design goals. We discuss the basic principles of frequency-domain multiplexing, the design and testing of the test chips, and the implementation of a practical system.

A frequency-domain SQUID multiplexer for arrays of transition-edge superconducting sensors

We describe the development of a frequency-domain multiplexer (MUX) to read out arrays of superconducting transition-edge sensors (TES). Fabrication of large-format arrays of these sensors is becoming practical; however, reading out each sensor in the array is a major instrumental challenge. Frequency-domain multiplexing can greatly simplify the instrumentation of large arrays by reducing the number of SQUIDs (superconducting quantum interference devices) and wires to the low temperature stages. Each sensor is AC biased at a different frequency, ranging from 380 kHz to 1 MHz. Each sensor signal amplitude-modulates its respective AC bias frequency. An LC filter associated with each sensor suppresses Johnson noise from the other sensors. The signals are combined at a current summing node and measured by a single SQUID. The individual signals from each sensor are then lock-in detected by room temperature electronics. Test chips with fully lithographed LC filters for up to 32 channels have been designed and fabricated. The capacitance and inductance values have been measured and are close to the design goals. We discuss the basic principles of frequency-domain multiplexing, the design and testing of the test chips, and the implementation of a practical system.

Frequency-domain SQUID multiplexing of transition-edge sensors

We describe our frequency-domain readout multiplexer for transition-edge sensor (TES) bolometers and present measurements of an eight-channel multiplexer. Each sensor is biased with a sinusoidal bias at a distinct frequency. As the sensor absorbs power, it amplitude-modulates its sinusoidal bias. Sensor currents are summed and measured with a single superconducting quantum interference device (SQUID) array. The SQUID array consists of 100 dc-SQUIDs in series and is operated with shunt feedback electronics which have a slew rate of 1.210/sup 7/ /spl Phi//sub 0//s. A tuned filter consisting of an inductor and capacitor are placed in series with each sensor to both limit the bandwidth of the Nyquist noise from each sensor and to allow us to bias all multiplexed sensors with a common wire. We place an upper limit on crosstalk between adjacent channels of 0.004, well below our design requirements. Demodulated noise spectra from multiplexed sensors show the expected white noise levels at frequencies above 200 mHz.