Doktorantūras seminārs 2015.gada 28. janvāris

1. Signālu reprezentācija, pārraide un apstrāde balstīta uz precīzi novērtētiem specifisku notikumu laika momentiem Doktorants: Armands Mezeriņš Darba vadītājs: Doktorantūras seminārs 2015.gada 28. janvāris

2. Darbamērķis Darbamērķisirefektīvasmetodesizstrādesignāludiskretizācijai un pamataapstrādei, izmantojottikailaikainformāciju.

3. t1 t2 t3 Time scale • 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). Events – NIM logic pulses Event Timer A033-ET Resolution 3 ps RMS Maximum rate 20MSPS Average rate 30KSPS

4. 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

5. APPLICATIONS OF EVENT TIMERS Laser Time Transfer (LTT) in collaboration with institutions of China Academy of Sciences. • 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 Laser Time Transfer Principle ΔT = τup –TS- TG

6. 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

7. 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 • Increasedlaser pulse power/distance/reliability

8. 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

9. Conventional interpolation methods • (Time interval stretching, Verniermethod 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.

10. 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.

11. 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).

12. 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.

13. ANALOG SIGNAL REPRESENTATION IN THE TIME DOMAIN

14. ANALOG SIGNAL REPRESENTATION IN THE TIME DOMAIN • The conversion of the analog signal into representative eventsis 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)

15. a) t ANALOG SIGNAL REPRESENTATION IN THE TIME DOMAIN b) t c) t d) 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;

16. 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.

17. a) t RECONSTRUCTION OF DIGITAL SIGNAL SAMPLE VALUES offset b) Time diagrams illustrating received PPM signal a) receiver clock; b) received PPM signal (including phase offset, propagation delay); t t propagation delay Time diagram, illustrating reconstructed digital signal samples with reference sine-wave (including phase offset, propagation delay).

18. PRACTICAL IMPLEMENTATION

19. PRACTICAL IMPLEMENTATION OF THE CONSIDERED AEC METHOD Block diagram of the hardware implementation of analog-to-event converter circuit

20. T/H Amplifier Input Analog Signal Dual Comparators PRACTICAL IMPLEMENTATION OF THE CONSIDERED AEC METHOD Output Buffer Amplifier FF1 FF2 Sine-wave Reference Signal Output PPM 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.

21. INPUT SIGNAL DIAGRAM Oscillogram illustrating the reference sine-wave, input analog signal and T/H sampled output signal. OUTPUT SIGNAL DIAGRAM Oscillogram illustrating the reference sine-wave, T/H sampled output signal and the output NIM signal (PPM signal for transmitting).

22. TIMING JITTER ESTIMATION OF THE PPM SIGNAL Block diagram of the experimental hardware setup

23. TIMING JITTER ESTIMATION OF THE PPM SIGNAL, INPUT DC 0V INTERVALS between timed events with standard deviation (RMS) are shown:

24. TIMING JITTER ESTIMATION OF THE PPM SIGNAL, SINE INPUT, 2.5MHZ, AIN =1V ZOOMED BANDS: [slide28]

25. EXPERIMENTS WITH OPTICAL INSTRUMENTATION

28. 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

29. Timing data obtained from HAMAMATSU LIGHT PULSER output SYNC OUT, DC INPUT 0V

30. 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

31. Timing data obtained from APD photo detector output – DC INPUT 0V

32. SIGNAL SAMPLES PROCESSING

33. Transfer curve of the time-based ADC

34. EXPERIMENTS WITH SIGNAL SAMPLES PROCESSING, DC 0V input Intervals Intervals Restored signal samples with resolved phase bias Restored signal samples

35. EXPERIMENTS WITH SIGNAL SAMPLES PROCESSING, FIN=1MHz AIN=1V, SINE

36. SPECTRAL ANALYSIS, FIN=1MHz, AIN = 1V, SINE, Signal reconstructed from timing results.

37. DYNAMIC INPUT

38. 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.

39. 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).

40. 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.

41. 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.

42. SINEWAVE INPUT, AIN = 10dBm (0.707V rms), FIN = 0.98999MHZ

43. FFT SPECTRUM

44. SINEWAVE INPUT, AIN = 9dBm (0.707V rms), FIN = 0.98999MHZ

45. SINEWAVE INPUT, AIN = 10 dBm (0.707V rms), FIN = 0.98999MHZ

46. SINEWAVE INPUT, AIN = 11 dBm (0.707V rms), FIN = 0.98999MHZ

47. STATIC INPUT

48. TIME CODES modulo 100ns and reconstructed DIGITAL SIGNAL for 0V DC INPUT (10 measurements) • 10 adjacent measurement series are plotted versus time. • 16384samples 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).

49. 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.

50. 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.