Signālu reprezentācija, pārraide un apstrāde balstīta uz precīzi novērtētiem specifisku...
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Transcript of Signālu reprezentācija, pārraide un apstrāde balstīta uz precīzi novērtētiem specifisku...
Signālu reprezentācija, pārraide un apstrāde balstīta uz precīzi novērtētiem
specifisku notikumu laika momentiem
Doktorants: Armands Mezeriņš
Darba vadītājs:
Doktorantūras seminārs 2015.gada 28. janvāris
DARBA MĒRĶIS
Darba mērķis ir efektīvas metodes izstrāde signālu diskretizācijai un pamata
apstrādei, izmantojot tikai laika informāciju.
INTRODUCTION
IECS time-measurement laboratory:
•R&D activities in the area of high-precision Event Timing (40 years of studies).
The definition of event timing is
- measurement of the time instants when some events occur.
In our case events are represented by leading edges of uniform
electrical pulses (NIM).
Time scalet1 t2 t3
Events – NIM logic pulsesEvent Timer A033-ETResolution 3 ps RMSMaximum rate 20MSPSAverage rate 30KSPS
APPLICATIONS OF EVENT TIMERS
Satellite Laser Ranging (SLR at KHz rate) in collaboration with “International Laser
Ranging Service” network, LU AI, China Academy of Sciences.
• Time-of-Flight (TOF) measurement.
• A033-ET is used in more than 50 ILRS centers
globally
APPLICATIONS OF EVENT TIMERS
Laser Time Transfer (LTT) in collaboration with institutions of China Academy of Sciences.
ΔT
Emitted pulse
up down
GT ST
ST
up down
Satellite time
Ground time
Received pulse
Returned pulse
1PPS
1PPS
ΔT
Emitted pulse
up down
GT ST
ST
up down
Satellite time
Ground time
Received pulse
Returned pulse
1PPS
1PPS
Laser Time Transfer Principle ΔT = τup –TS- TG
•Synchronization of remote ultra-stable clocks
•Laser link between distant clocks with time
stability of a few picoseconds and 100ps
accuracy
•2 A033-ET are used at Schanghai SLR station
SEARCH FOR NEW APPLICATIONS FOR CURRENT TIMING TECHNOLOGY
•Signal analysis, pulse generator jitter analysis
•Time-resolved fluorescence spectroscopy,
Time Correlated Single Photon Counting
•Absolute Gravimetry
•LIDAR (Light Detection And Ranging),
terrestrial 3D laser scanners Time-resolved fluorescence measurement with TCSPC
APPLICATION IN OPTICAL COMMUNICATION?
Free-space optical communication (FSO) - an optical communication technology that
uses light propagating in free space to wirelessly transmit data.
In this case, the use of Pulse Position Modulation with direct transmitted/received
pulse time measurements performed with high accuracy (approx. 10ps):
•Low duty cycle of laser pulses
•Cannot compete with data transfer rates
•Increased laser pulse power/distance/reliability
PRINCIPLE OF ENHANCED EVENT TIMING METHOD -TWO COMPLEMENTING MEASUREMENTS
•Coarse time measurement with a counter that
continuously counts clock pulses
•Interpolation measurement within the clock interval
Conventional interpolation methods
(Time interval stretching, Vernier method etc.) practically implemented usually
entail:
•Considerable hardware complexity;
•Very careful design and adjustment.
EET method is Digital Signal Processing based method:
•Highly complicated analog circuits are replaced with typical capabilities of DSP;
•Decreased hardware complexity, increase in reliability.
GENERAL IDEA OF DSP BASED EET METHOD
• Generate specific secondary analog signal
at the moment defined by the input event
• Digitize this event-initiated signal
• Digital processing of the signal samples
Proper processing results in an estimate of the secondary signal position on the time axis.
Practical implementation of the EET method – Event Timer A033-ET overview
•Computer based instrument intended for SLR apps.
•Single-shot RMS resolution of 3 ps at measurement rate of 20MSPS (dead
time of 50 ns).
•Two inputs A and B to alternately measure Start and Stop events in the
same channel. Additional special mark in the time-tag identifies the input.
•Two basic modes for measurements: Continuous mode and Cyclical mode.
•Basic software - “client-server” architecture based applications and sample
program in C (includes all necessary routines for data processing that is
directly obtained from device).
Event Timer A033-ET Typical Performance Characteristics
Single-shot RMS resolution
•Specifies the practicable A033-ET precision
•Obtained in a direct repetitive measurement of a periodic test signal
that has a jitter much smaller than the expected errors produced by the
timer
•For the A033-ET it is defined as the standard deviation of total error in
measurement of time intervals between events
•Typically in the range of 3-4 ps.
ANALOG SIGNAL REPRESENTATION
IN THE TIME DOMAIN
• The conversion of the analog signal into representative events is performed using
uniformly sampled Pulse Position Modulation of the input analog signal.
Block diagram of the proposed architecture for analog-to-time domain converter (analog-to-event converter)
ANALOG SIGNAL REPRESENTATION IN THE TIME DOMAIN
a)
b)
c)
d)
t
t
t
t
Time diagrams, illustrating analog signal
conversion into PPM signal and transmitting in
accordance to considered method. a) analog
input and T/H signal; b) T/H and reference
signal; c) formed uniformly sampled PWM
signal; d) transmitted uniformly sampled PPM
signal representing the analog input signal;
ANALOG SIGNAL REPRESENTATION IN THE TIME DOMAIN
RECONSTRUCTION OF DIGITAL SIGNAL SAMPLE VALUES
• It is assumed that the time scales of the transmitter and the receiver are synchronized
• Demodulation of the PPM pulse sequence is done by timing of t(k) and direct restoration of signal
samples using the expression:
x(k)= A cos[2πf(t(k) – φ)],
where A - reference sine-wave amplitude;
f - reference sine-wave signal frequency;
φ – phase offset;
Block diagram of the receiver for recovery of the representative signal samples from received PPM signal.
offset
propagation delay
t
t
a)
b)
t
Time diagrams illustrating received PPM
signal
a) receiver clock;
b) received PPM signal (including phase
offset, propagation delay);
Time diagram, illustrating reconstructed
digital signal samples with reference
sine-wave (including phase offset,
propagation delay).
RECONSTRUCTION OF DIGITAL SIGNAL SAMPLE VALUES
PRACTICAL
IMPLEMENTATION
PRACTICAL IMPLEMENTATION OF THE CONSIDERED AEC METHOD
Block diagram of the hardware implementation of analog-to-event converter circuit
PRACTICAL IMPLEMENTATION OF THE CONSIDERED AEC METHOD
T/H Amplifier
Dual Comparators
FF1 FF2 Output Buffer Amplifier
Output PPM Signal
Input Analog Signal
Sine-wave Reference Signal
Hardware design of the analog-to-event converter.
Created by experienced engineer of time-measurement laboratory. The practical operation of this circuit defines the success of the results. Or necessity to rebuild the prototype.
INPUT SIGNAL DIAGRAM
Oscillogram illustrating the reference sine-
wave, input analog signal and T/H sampled
output signal.
Oscillogram illustrating the reference
sine-wave, T/H sampled output signal and
the output NIM signal (PPM signal for
transmitting).
OUTPUT SIGNAL DIAGRAM
TIMING JITTER ESTIMATION OF THE PPM SIGNAL
Block diagram of the experimental hardware setup
TIMING JITTER ESTIMATION OF THE PPM SIGNAL, INPUT DC 0V
INTERVALS between timed events with standard deviation (RMS) are shown:
TIMING JITTER ESTIMATION OF THE PPM SIGNAL, SINE INPUT, 2.5MHZ, AIN =1V
ZOOMED BANDS:
0 200 400 600 800 1000-2
-1
0
1
2
EXPERIMENTS WITH OPTICAL
INSTRUMENTATION
EXPERIMENTAL SETUP WITH OPTICAL INSTRUMENTATION
•Timing jitter estimation of the PPM signal prior transmitting
•Timing data obtained from HAMAMTSU PICOSECOND LIGHT PULSER output SYNC OUT
Block diagram of the experimental hardware setup
Timing data obtained from HAMAMATSU LIGHT PULSER output SYNC OUT, DC INPUT 0V
EXPERIMENTAL SETUP WITH OPTICAL INSTRUMENTATION
•Timing jitter estimation of the PPM signal transmitted via optical channel
•Timing data obtained from APD photo detector output
Block diagram of the experimental hardware setup
Timing data obtained from APD photo detector output – DC INPUT 0V
SIGNAL SAMPLES PROCESSING
Transfer curve of the time-based ADC
0 50 100 150 200-1
0
1
Time(ns)
Vol
tage
(V
)
Input C.T. Signal vs.Time
050
100150
0 10 20 30 40 50 60 70 80 90
100
Time(ns)
Time(modulo 100ns) (ns)
Output Tim
e(modulo 100ns) vs. Tim
e
0 20 40 60 80 100-2
-1
0
1
2
Time (modulo 100ns) (ns)
Inpu
t V
olta
ge (
V)
TRANSFER CURVE VS. TIME
0 2000 4000 6000 8000 10000 12000 14000 16000 1800099.96
99.98
100
100.02
100.04Time intervals
Interval number (n)
Inte
rval (n
s)
5391.9788 5391.979 5391.9792 5391.9794 5391.9796 5391.9798 5391.98 5391.9802 5391.9804
-1.266
-1.265
-1.264
-1.263
Restored signal samples
Time (s)
Am
plitu
de (V
)
5391.9788 5391.979 5391.97925391.97945391.97965391.9798 5391.98 5391.98025391.9804
-2
-1
0
1
2
x 10-3 Restored signal samples with resolved phase bias
Time (s)
Am
plitu
de (V
)
EXPERIMENTS WITH SIGNAL SAMPLES PROCESSING, DC 0V input
Intervals Intervals
Restored signal samples Restored signal samples with resolved phase bias
1820.0601 1820.0601 1820.0601 1820.0601 1820.0601 1820.0601
-1.5
-1
-0.5
Restored signal samples
Time (s)
Am
plitu
de (
V)
1820.0601 1820.0601 1820.0601 1820.0601 1820.0601 1820.0601-1
-0.5
0
0.5
1Restored signal samples with resolved phase bias
Time (s)
Am
plitu
de (
V)
EXPERIMENTS WITH SIGNAL SAMPLES PROCESSING, FIN=1MHz AIN=1V, SINE
SPECTRAL ANALYSIS, FIN=1MHz, AIN = 1V, SINE,
Signal reconstructed from timing results.
9.7 9.8 9.9 10 10.1 10.2
x 105
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Amplitude Spectrum |Y(f)| of restored signal samples
Frequency (Hz)
Magnitude |Y
(f)| (
V)
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
x 106
-150
-100
-50
0Amplitude Spectrum |Y(f)| of restored signal samples
Frequency (Hz)
Magnitude |Y
(f)| (
dB
V)
DYNAMIC INPUT
EVALUATING THE AC PERFORMANCE OF THE TIME-BASED ADC
DYNAMIC PERFORMANCE SPECIFICATION:•The ADC performance (accuracy of its output) typically is quantified by two main categories – DC (or Static) and AC
(or Dynamic) input specifications.
•The Dynamic input performance is quantified with: SINAD (signal-to-noise-and-distortion ratio), ENOB (effective
number of bits), SNR (signal-to-noise ratio), THD (total harmonic distortion) and SFDR (spurious free dynamic
range).
•FFT-based signal analysis for ADC evaluation - using Fast Fourier Transform of the dynamic input (single tone, low-
noise, pure sine-wave) to extract AC specifications.
EVALUATING THE AC PERFORMANCE OF THE TIME-BASED ADC
•COHERENT SAMPLING – is performed to accurately evaluate noise and distortion spectral components in the
frequency domain. The integer number of signal periods firs into acquisition time interval. The input signal
frequency precisely coincides with k-th spectral line in FFT frequency grid.
•The criterion for coherent sampling is given by equation:
FIN / FS = NWINDOW / NRECORD,
Where FIN –frequency of the periodic input signal, FS – sampling/clock
frequency of the ADC under test, NWINDOW – integer prime number of
periods of the input waveform within the sampling window, NRECORD –
number of samples in the sampling window (FFT size, power of two).
EVALUATING THE AC PERFORMANCE OF THE TIME-BASED ADC
DYNAMIC PERFORMANCE SPECIFICATION
•WINDOW SAMPLING – non-integral number of signal periods fits into the acquisition interval. The frequency
component energy spreads across adjacent frequency lines – spectral leakage. (amplitude accuracy errors). Window
functions are applied to time-domain waveform prior FFT.
•The Hann, 4-term Blackman-Harris window functions are applied. Coherent gain factor scaling.
Typical FFT output used for computing
•The FFT plot below shows example of coherent sampling. Note the regions marked by circles of different colors.
These regions are used to compute the power of fundamental, the DC and harmonics. The noise power is the total
signal power, excluding that of fundamental, harmonics and DC.
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
x 106
-140
-120
-100
-80
-60
-40
-20
0SINAD 38dBc SNR 48.7dBc THD -38.3dBc SFDR 41.3dBc ENOB 6.4bits @ FIN = 0.9729MHZ AIN = 1.56V
Frequency (Hz)
Pow
er |Y
(f)|2 (
dBF
S)
1st
2nd3rd
4th 5th6th
7th
8th
9th
10th
SINEWAVE INPUT, AIN = 10dBm (0.707V rms), FIN = 0.98999MHZ
6684.1229 6684.1229 6684.1229 6684.122915
20
25
30
tcodes(modulo 100ns)
Time(s)
tcod
es(m
odul
o 10
0)(n
s)
6684.1229 6684.1229 6684.12296684.1229 6684.1229
68
70
72
74
76
78
80
82
tcodes(modulo 100ns) After Correction
Time(s)
tcod
es(m
odul
o 10
0)(n
s)
6684.1229 6684.12296684.1229 6684.12296684.1229
-1
-0.5
0
0.5
Signal Prior Correction
Time(s)
Am
plitu
de(V
6684.1229 6684.1229 6684.1229 6684.1229 6684.1229
-1
-0.5
0
0.5
1Signal After Correction
Time(s)
Am
plitu
de(V
FFT SPECTRUM
SINEWAVE INPUT, AIN = 9dBm (0.707V rms), FIN = 0.98999MHZ
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
x 106
-150
-100
-50
0SINAD 46.7dB SNR 55.1dB THD -47.4dB SFDR 50.8dBc ENOB 7.5bits @ FIN = 0.98999MHZ AIN = 9dBm
Frequency(Hz)
Pow
er(d
B)
1st
2nd3rd 4th 5th6th7th8th9th10th
SINEWAVE INPUT, AIN = 10 dBm (0.707V rms), FIN = 0.98999MHZ
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
x 106
-150
-100
-50
0SINAD 46.2dB SNR 56.9dB THD -46.6dB SFDR 50.1dBc ENOB 7.4bits @ FIN = 0.98999MHZ AIN = 10dBm
Frequency(Hz)
Pow
er(d
B)
1st
2nd3rd 4th 5th6th7th8th9th
10th
SINEWAVE INPUT, AIN = 11 dBm (0.707V rms), FIN = 0.98999MHZ
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
x 106
-150
-100
-50
0
50SINAD 43.7dB SNR 55.4dB THD -44dB SFDR 48.1dBc ENOB 7bits @ FIN = 0.98999MHZ AIN = 11dBm
Frequency(Hz)
Pow
er(d
B)
1st
2nd 3rd 4th 5th6th7th
8th9th10th
STATIC INPUT
TIME CODES modulo 100ns and reconstructed DIGITAL SIGNAL for 0V DC INPUT
(10 measurements)
• 10 adjacent measurement series are plotted versus time. • 16384 samples spaced by 100ns (totally 1.6ms interval) in one measurement serie.• 930ms intervals (gaps) between two adjacent measurements, to transfer data into PC (1 time-tag per
57us).
TIME CODES MOD 100ns and DIGITAL SIGNAL for 0V DC INPUT
(ZOOMED 5th/10 measurement)
Envelope modulation of the short-term DC input in the circuit.
That is not expected operation of the circuit.
TIME CODES MOD 100ns and DIGITAL SIGNAL for 0V DC INPUT
(ZOOMED 6th/10 measurement)
The short-term deviation is approximately 6 ps for 0V DC input.
These are expected accuracy characteristics of the citrcuit.
TIME CODES MOD 100ns and DIGITAL SIGNAL for 0V DC INPUT
(ZOOMED 10th/10 measurement)
Ripples in the short-term deviation possibly due to the self-
resonance in the circuit.
DC INPUT AND ITS DFT
SPECTRUM 10kHz with 10Hz resolution
50Hz component frequency
TIME CODES modulo 100ns and reconstructed DIGITAL SIGNAL for 0V DC INPUT
(100 measurements)
The long-term deviation is unacceptably high. Possibly
it is due to the 50Hz component.
Conclusions
•The practical implementation of the time-based ADC is specified in terms
of its Dynamic and (partially) Static performance.
•The inaccuracy of its output ,due to the circuit self-resonance or
interference, needs to be eliminated.
•The prottotype has to be rebuild according to the low-noise design
principles.
Thanks for attention!