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!