IEEE Instrumentation & Measurement - September 2023 - 15

IS
Clk
Carry out
FF0
DQ
aCLR
FF1
DQ
aCLR
DQ
aCLR
DQ
aCLR
FF2
FF3
Datad
Datae1
FFn
DQ
aCLR
(a)
4-input
LUT
Dataf1
Carry out
(b)
(c)
Fig. 4. Simplified representation of the basic elements in FPGAs for TDL implementation. (a) General representation of TDL. (b) Adaptive Logic Module available
in Intel Cyclone V and Cyclone 10 families. (c) Slice representation. Available in 7-series Xilinx FPGAs.
pulses were propagated. This method was initially explored
in 2008 [8], when two variants were proposed. The first is the
Wave Union A (WUA) method; a signal of four transitions is
produced to perform four measurements in each clock cycle
for each propagated pulse train. The second is the Wave
Union B (WUB) method, in which a ring oscillator is used
to produce an infinite number of pulses/transitions once a
launcher is triggered, performing N measurements in each
clock cycle. In [9], an in-depth analysis of this methods is presented.
With these strategies, it is also possible to improve
precision at the expense of higher use of hardware resources
in the encoder component. One inconvenience of this strategy
is that a long dead-time is required, which sometimes
makes it infeasible for FPGAs' manufactured advanced processes
[10]. Another PS method is producing a Pulse whose
Width is Equivalent to Fine Measurement (PWEFM) [3],
[11]. This method has the advantage that the number of ones
latched by the capture module is directly proportional to
FM. Fig. 5 depicts these most commonly used shapes.
Encoder
Besides CC, the encoder receives the TDL status to obtain a
binary representation of the measurement. Overall, the CC
encoding does not represent a challenge as the one needed to
process the FM. When PS is not used, a logic '1' is entered into
the TDL; then, a 1-0 transition is shifted from the input. The
position to which this transition propagates within the TDL
corresponds to FM. In this case, what is captured is a thermometric
code, which the ones-counter encoder can convert into
a binary code. Nevertheless, these signals are usually captured
with errors, mainly in the transition zones. These errors
September 2023
are known as bubbles which occur mainly due to nonhomogeneous
routing and timing violations during the capture. For
the mentioned example, the ones-counter encoder method has
been effectively used in [11] due to the global ability to correct
for bubbles, as it does not depend on the tap sequence. This
method can also be effective with the PWEFM strategy. For
WU launchers, encoding methods to find transitions position
are required [9], [12].
Calibration
The second post-processing step (calibration) consists of compensating
measurement against the process, voltage, and
temperature variations (PVT). Recent studies have found
that the bin-bin calibration is the most suitable for TDL-based
DQ
aCLR
01
Carry in
CLK
4-input
LUT
Dataf0
Datac
Datab
Dataea
Datae0
4-input
LUT
Carry in
CLK
FF0
DQ
aCLR
FF1
4-input
LUT
DQ
aCLR
FF2
DQ
aCLR
FF3
06/LUTD
05/LUTD
DX
06/LUTC
05/LUTC
CX
06/LUTB
05/LUTB
BX
06/LUTA
05/LUTA
AX
FF0
DQ
aCLR
FF1
D Q
aCLR
FF2
D Q
aCLR
FF3
D Q
aCLR
BQ
AMUX/DQ
AMUX
AQ
CQ
BMUX/DQ
BMUX
DMUX
DQ
CMUX/DQ
CMUX
DMUX/DQ
W/o PS
PWEFM
11 11 11 00 00
00 00 11 00 00
WUA 00 10 10 00 00
WUB 01 01 01 01 01
Fig. 5. Examples of different pulse shape options to be created from the
input signal arrival.
IEEE Instrumentation & Measurement Magazine
15

IEEE Instrumentation & Measurement - September 2023

Table of Contents for the Digital Edition of IEEE Instrumentation & Measurement - September 2023

Contents
IEEE Instrumentation & Measurement - September 2023 - Cover1
IEEE Instrumentation & Measurement - September 2023 - Cover2
IEEE Instrumentation & Measurement - September 2023 - Contents
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