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Journal ArticleDOI

Performance of 20:1 multiplexer for large area charge readouts in directional dark matter TPC detectors

27 Feb 2018-Journal of Instrumentation (IOP Publishing)-Vol. 13, Iss: 02, pp 02031
TL;DR: In this article, an expanded LMH6574 multiplexer system with a capability of reducing the number of readouts in such TPC detectors by a factor of 20 is presented.
Abstract: More target mass is required in current TPC based directional dark matter detectors for improved detector sensitivity. This can be achieved by scaling up the detector volumes, but this results in the need for more analogue signal channels. A possible solution to reducing the overall cost of the charge readout electronics is to multiplex the signal readout channels. Here, we present work on an expanded LMH6574 multiplexer system with a capability of reducing the number of readouts in such TPC detectors by a factor of 20. Results indicate that the important charge distribution asymmetry along an ionization track is retained after multiplexed signals are demultiplexed.

Summary (2 min read)

1 Introduction

  • The desire to scale-up directional dark matter (DM) TPCs (time projection chambers) with low energy thresholds has been building in recent years [1–4].
  • A ton-year scale directional DM detector is essential to reach the required sensitivity for DM-neutrino background discrimination beyond the so-called neutrino floor [5, 6].
  • The cost of electronics readout required to build this massive TPC detector for directional DM detection is an issue for the technology.
  • The proposed CYGNUS-10 detector with a fiducial volume of 10 m3 could potentially result in about 105 channels.
  • Analogue multiplexers are produced mainly from field-effect transistors (FET), known as FET analogue switches which allow many signal channels to be sampled and combined into a common signal stream at a given temporal interval [10, 11].

2 Design and construction of the 20:1 signal MUX

  • To multiplex 20 analogue signal channels, five TI-LMH6574 chips were used.
  • This is also true for the shutdown (SD) and the grounded chip enable signal pins to allow for centralised chip control and signal read out.
  • Analogue signal inputs were connected on the board using an MDR-50 connector via a ribbon cable ).
  • The issue of crosstalk induced by separated analogue-digital grounds was avoided by not running traces across the two grounds.
  • For this MUX system, a total of about 0.89 µs delay and data acquisition system (DAQ) dead time are expected considering the 8 ns channel switch time of the individual chips.

3 Test system for the 20:1 MUX

  • A new miniature TPC detector was built to test the MUX electronics using analogue signals from 5.5 MeV alpha interactions.
  • Wires from the pulley were then tensioned and fixed on one of the four 1 mm threaded wire-landing rods positioned on a wire-winding frame.
  • It can be seen that the maximum gains were obtained at higher grid wire voltages >0.8 kV.
  • This is not a problem for this experiment as all the measurements were performed using constrained gas pressures (250 - 260 Torr).
  • Data from the miniature detector was multiplexed and demultiplexed using an NI FPGA based LabVIEW DAQ.

4 MUX Results and Discussion

  • The 20 analogue signal inputs from the one-plane MWPC based detector were multiplexed and demultiplexed at 0.625 MHz per signal channel (12.5 MHz for 20 channels) using one ADC channel of the NI module.
  • As expected, each of the Bragg peaks was observed on the anode wire located toward the end of – 10 – the range of the event track.
  • Results show that the average magnitude of the observed Bragg peak after the signals were demultiplexed is 65 mV less than the raw signal results.
  • This is mainly due to signal loss in the multiplexer system.
  • These dead times of the MUX system and efficiency (>90%) of the noise suppression can contribute to signal loss in the demultiplexed data.

5 Conclusion

  • A one-plane MWPC-based time projection chamber detector was designed, built and used to test the feasibility of a new 20:1 analogue signal multiplexer as a possible readout for a future massive directional dark matter detectors.
  • 1 multiplexer was built using expanded LMH6574 – 11 – chips from Texas Instruments, also known as The 20.
  • Signal multiplexing is motivated and can be a possible means to reduce the cost of signal readouts in massive TPC detectors without compromising the detector sensitivity to event x-y position.
  • Results obtained from this multiplexer system are encouraging and it has demonstrated that ionization charge distribution along alpha tracks can be reconstructed from demultiplexed signals.

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This is a repository copy of Performance of 20:1 multiplexer for large area charge
readouts in directional dark matter TPC detectors.
White Rose Research Online URL for this paper:
http://eprints.whiterose.ac.uk/125937/
Version: Accepted Version
Article:
Ezeribe, A.C., Robinson, M., Robinson, N. et al. (3 more authors) (2018) Performance of
20:1 multiplexer for large area charge readouts in directional dark matter TPC detectors.
Journal of Instrumentation, 13 (02). P02031. ISSN 1748-0221
https://doi.org/10.1088/1748-0221/13/02/P02031
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Submitted to JINST
Performance of 20:1 multiplexer for large area charge
readouts in directional dark matter TPC detectors
A. C. Ezeribe,
1
M. Robinson, N. Robinson, A. Scarff, N. J. C. Spooner and L. Yuriev
Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, U.K.
E-mail:
a.ezeribe@sheffield.ac.uk
Abstract: More target mass is required in current TPC based directional dark matter detectors
for improved detector sensitivity. This can be achieved by scaling up the detector volumes, but
this results in the need for more analogue signal channels. A possible solution to reducing the
overall cost of the charge readout electronics is to multiplex the signal readout channels. Here,
we present a multiplexer system in expanded mode based on LMH6574 chips produced by Texas
Instruments, originally designed for video processing. The setup has a capability of reducing the
number of readouts in such TPC detectors by a factor of 20. Results indicate that the important
charge distribution asymmetry along an ionization track is retained after multiplexed signals are
demultiplexed.
Keywords: MUX, Demultiplexer, DeMUX, TPC, Charge readout
1Corresponding author.
arXiv:1711.00943v2 [physics.ins-det] 12 Mar 2018

Contents
1 Introduction 1
2 Design and construction of the 20:1 signal MUX 2
3 Test system for the 20:1 MUX 4
4 MUX Results and Discussion 8
5 Conclusion 11
1 Introduction
The desire to scale-up directional dark matter (DM) TPCs (time projection chambers) with low
energy thresholds has been building in recent years [
14]. A ton-year scale directional DM detector
is essential to reach the required sensitivity for DM-neutrino background discrimination beyond the
so-called neutrino floor [
5, 6]. The neutrino floor is a parameter space where solar, atmospheric
and diffused supernovae neutrino backgrounds are expected in direct DM search experiments [
57].
Also, in a case of a DM detection claim, a directional detector would be necessary to confirm
the Galactic origin and anisotropic nature of the signal [8]. However, the cost of electronics
readout required to build this massive TPC detector for directional DM detection is an issue for
the technology. For instance, the proposed CYGNUS-10 detector with a fiducial volume of 10 m
3
could potentially result in about 10
5
channels.
One of the possible ways of reducing the readout cost is through signal multiplexing. In this
work, we test a 20:1 multiplexer (MUX) using TI-LMH6574 chips sourced from Texas Instruments
(TI) [
9] in expanded mode. Analogue multiplexers are produced mainly from field-effect transistors
(FET), known as FET analogue switches which allow many signal channels to be sampled and
combined into a common signal stream at a given temporal interval [
10, 11]. The TI-LM6574 chip
illustrated in Figure
1 is a high performance 4:1 analogue video multiplexer comprising a 14-pin
device embedded in a small outline integrated circuit (SOIC) surface mount package. The four input
channels of the TI-LM6574 MUX chip are marked as IN 0, IN 1, IN 2, and IN 3 in Figure 1. During
an operation, the signal in each of these input channels is selected using a unique signal address
generated with a pair of A0 and A1 digital control signals at a defined frequency and passed as the
output of the chip [
9]. For the experiment described here, the frequency of the A0 signal was set to
be a factor of 2 larger than the A1 signal so as to generate the required set of four digital addresses
for enabling each of the analogue input channels. The generated A0,A1 digital addresses for IN 0,
IN 1, IN 2 and IN 3 are 1,1 ; 0,1 ; 1,0 and 0,0, respectively. To recover the original signal, the
multiplexed signal is demultiplexed using the reference multiplexing frequency. This was achieved
by using NI 5751 digitizer adapter module [
12] of 16 ADC channels, operated with a PXI-7953R
1

Figure 1: Illustration of the 4:1 analogue multiplexer. The IN 0, IN 1, IN 2 and IN 3 are the four
analogue input signal channels while A0 and A1 are the digital signals (addresses) for selecting a
channel to be sampled. The switching nature of the output stream of the chip between the input
channels is illustrated with an arrow [
9].
NI FlexRIO field programmable gate array (FPGA) device [
13] from National Instruments (NI)
Corporation.
2 Design and construction of the 20:1 signal MUX
To multiplex 20 analogue signal channels, five TI-LMH6574 chips were used. This was achieved
by connecting together all the digital address (A0 and A1) pins of the chips using a custom-made
EAGLE [
14] printed circuit board (PCB). This is also true for the shutdown (SD) and the grounded
chip enable (
EN, see Figure 1) signal pins to allow for centralised chip control and signal read out.
This is known as expanded mode operation. The EAGLE schematic layout view of the MUX PCB
and the manufactured 20:1 MUX board are shown in Figure 2. The SD signal is the chip switching
digital signal used for moving controls from one chip to another while in the expanded mode. The
five light red rectangular chips in Figure
2(a) are the TI-LMH6574 MUX chips. Analogue signal
inputs were connected on the board using an MDR-50 connector via a ribbon cable (see Figure
2(b)).
The analogue signal output of the board was read out using a BNC cable. To route the chip digital
control signals from the NI module to the board, a NI SCSI-68 connector and NI SHC68-68-EPM
cable were used. The MUX board was powered through a set of WAGO 236-412 wire-to-board
terminal connectors as shown in Figure
2(b).
Each of the input signal channels was terminated with a 550 resistor to reduce signal
reflections and ensure that any excess currents were properly grounded. These input termination
resistors are marked as R
IN0
, R
IN1
, R
IN2
, R
IN3
, R
T
and R
G
in Figure
1. Also, a 550 resistor was
used as the R
F
resistor to achieve a gain of 2, with an R
OUT
resistor of 50 on the output channel.
To achieve the required operational specification, the analogue ground was separated from the
digital ground to avoid noise coupling between the analogue and digital signals. However, when
this is not properly managed it can introduce crosstalk in the circuit since both planes may radiate
2

(a) EAGLE schematic layout of the MUX PCB.
(b) Manufactured MUX PCB in a shielding box.
Figure 2: EAGLE schematic layout for the 20:1 analogue signal multiplexing PCB (a) and the
manufactured board in a shielding box
(b). The five light red rectangular chips in (a) are the
TI-LMH6574 chips while the resistors are shown as smaller dark red rectangles. Analogue inputs
of each of the chips are labelled IN 0, IN 1, IN 2, IN 3 while the output connection is marked as Out.
Digital chip control signals are marked as A0, A1 and SD. The AGND and DGND are connections
to the analogue and digital grounds, respectively.
noise or act as noise antennas. Such noise is due to return currents flowing beneath each signal line.
This return current will always prefer to follow the path with lowest impedance hence disconnecting
these return paths with separated grounds may result in potential current loops especially when
3

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Frequently Asked Questions (2)
Q1. What have the authors contributed in "Performance of 20:1 multiplexer for large area charge readouts in directional dark matter tpc detectors" ?

Here, the authors present a multiplexer system in expanded mode based on LMH6574 chips produced by Texas Instruments, originally designed for video processing. 

A one-plane MWPC-based time projection chamber detector was designed, built and used to test the feasibility of a new 20:1 analogue signal multiplexer as a possible readout for a future massive directional dark matter detectors. Signal multiplexing is motivated and can be a possible means to reduce the cost of signal readouts in massive TPC detectors without compromising the detector sensitivity to event x-y position. Results obtained from this multiplexer system are encouraging and it has demonstrated that ionization charge distribution along alpha tracks can be reconstructed from demultiplexed signals.