1887
banner image
No data available.
Please log in to see this content.
You have no subscription access to this content.
No metrics data to plot.
The attempt to load metrics for this article has failed.
The attempt to plot a graph for these metrics has failed.
Code-division multiplexing for x-ray microcalorimeters
Rent:
Rent this article for
USD
10.1063/1.3684807
/content/aip/journal/apl/100/7/10.1063/1.3684807
http://aip.metastore.ingenta.com/content/aip/journal/apl/100/7/10.1063/1.3684807
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

(Color online) A four-row implementation of code-division multiplexing by flux summation (Φ-CDM). The TESs are dc-biased and thus on at all times. The current signal from TES j inductively couples to all four first-stage SQUID amplifiers (SQ1) with coupling polarity defined by column j in the modulation matrix W 4 (Eq. (1)). Oppositely oriented inductors (red/bold) produce a negative coupling polarity. Each row of inductors (shaded boxes) is transformer-coupled to one SQ1. Rows of SQ1s are operated with a standard TDM protocol (see Ref. 13): the rows are activated sequentially via I ad k , so the signal from one SQ1 at a time passes to a second-stage SQUID (SQ2). The output of SQ2 is routed to a 100-SQUID, series-array amplifier and then to room-temperature electronics. To keep the three-stage SQUID amplifier in its linear range, the multiplexer is run as a flux-locked loop (Ref. 13). The series array output (SA-out) is digitally sampled; a flux-feedback signal FB1 is then applied inductively to each SQ1 to maintain SA-out at a constant value.

Image of FIG. 2.
FIG. 2.

(Color online) Example raw and demodulated data from four detectors in a single 20 ms period. (a) The raw, encoded outputs, Rk, from the SQ1 in four-detector Φ-CDM (with vertical offsets for clarity). The SQ1 outputs correspond to rows 1–4 in Eq. (1). Manganese fluorescence x-rays struck TESs 3, 1, 2, and 4 at 0, 5, 7, and 11 ms. (b) The same data demodulated by application of to show the per-detector signal currents. The signal-to-noise is too high for the noise to be seen in this example.

Image of FIG. 3.
FIG. 3.

(Color online) The scaling of SQUID-amplifier noise in TDM and Φ-CDM. Noise was measured at 85 mK, with TESs superconducting to emphasize the amplifier noise (rather than TES noise) at high frequencies. The Johnson-noise contribution from the TES shunt resistor dominates below 1 kHz. The τ = L/R time constant of the shunt resistance and inductance in the TES bias loop causes the Johnson noise to roll off above 100 Hz. At high frequencies, the SQUID-amplifier noise is dominant. All measurements used t row = 640 ns and a 2.5 MHz, one-pole RC filter before the digitizer. (a) Noise from a single SQUID channel, referred to the first-stage SQUID, when read out with one, two, four, or eight TDM rows. Dotted lines show the single-row, high-f noise level (0.37 μΦ0/√Hz) multiplied by successive powers of . Due to aliasing, TDM amplifier noise grows with the number of rows as (see Ref. 7). (b) Noise in four- and eight-channel CDM readout. The signals, which have not been demultiplexed via the Walsh matrix, are referred to the first-stage SQUID. Lines are seen at the 60 Hz power line frequency and its harmonics. The dotted lines show the CDM-4, high- f noise level (0.65 μΦ0/√Hz) multiplied by 1 and . As in TDM, the aliased SQUID noise scales as . (c) Demodulated noise, referred to the TES current, in four- and eight-channel CDM. Both approach 19 pA/√Hz at high frequencies. We omit the unswitched channel from the average, making the 60 Hz line no longer visible.

Image of FIG. 4.
FIG. 4.

(Color online) Mn Kα x-ray fluorescence spectra measured separately by eight TES x-ray calorimeters read out with Φ-CDM. Spectra are offset vertically for clarity. These data have been analyzed with corrected Walsh codes and a linear arrival-time correction, and a Gaussian energy resolution has been fit, techniques described previously in Ref. 11. All detectors have multiplexed energy resolution better than 3 eV except for TES 1*—the only detector subject to low-frequency noise pickup in the SQUID amplifier chain. The Φ-CDM resolution matches or exceeds that found with equivalent TESs read out by TDM.

Loading

Article metrics loading...

/content/aip/journal/apl/100/7/10.1063/1.3684807
2012-02-13
2014-04-19
Loading

Full text loading...

This is a required field
Please enter a valid email address
752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Code-division multiplexing for x-ray microcalorimeters
http://aip.metastore.ingenta.com/content/aip/journal/apl/100/7/10.1063/1.3684807
10.1063/1.3684807
SEARCH_EXPAND_ITEM