A Multi-Channel Wide Range Time-to- Digital Converter with Better than 9ps RMS Precision for Pulsed Time-of-flight Laser Rangefinding

Transcription

1 A Multi-Channel Wide Range Time-to- Digital Converter with Better than 9ps RMS Precision for Pulsed Time-of-flight Laser Rangefinding Jussi-Pekka Jansson, Antti Mäntyniemi and Juha Kostamovaara Department of Electrical Engineering University of Oulu Oulu, Finland

2 2 Overview Consept of pulsed TOF laser radar Operation Requirements for TDC Techniques/structures for high precision measurement Designed 7-channel high precision TDC Operation Architecture Measurement results

3 3 Concept of pulsed laser rangefinder The measurement target is shot with a laser pulse TDC solves the propagation time of the laser pulse Propagation time equals the distance of the target Laser Pulser Transmitter Fiber ASIC #2 TDC DISTANCE Receiver Channel Receiver Channel ASIC #1 Start Fiber Stop Fiber Measurement Head Target R c t 2

4 54mm Minifaros project A miniature laser scanner for traffic perception 4 Anti-collision, proximity sensor, automatic cruise control TDC Dimensions (80mm 98mm 127mm) Minifaros project (part of the 7th Framework Programme, funded by the European Commission) 46mm Receiver Channel

5 5 Requirements Why multiple measurement channels? Partly reflections from unwanted targets before the actual target Cover window, rain, fog Several pulses can arrive to the TDC Largest error source in pulsed TOF measurement: Timing walk error New compensation techniques (Nissinen et al. 2009, Kurtti et al. 2011) Require width or slew rate information of the stop pulse

6 Key techniques (1): Nutt-based measurement principle: external reference source, counter and interpolator 6 Counter counts the full clock cycles between the timing signals long measurement range Interpolator solves the exact locations of the timing signals within the reference clock cycles high resolution

7 7 Key techniques (2): -Interpolation in two nested levels 1 st level interpolates within the resolution of counter 2 nd level interpolates only within the resolution of the 1 st level low number of delay elements and registers

8 8 Key techniques (3) -Reference recycling delay line as the 1 st interpolation level Cascaded delay elements create interpolation time samples with gate delay resolution 0.35µm CMOS) Same short delay line is used several times per reference clock cycle low nonlinearity, low reference clock frequency

9 9 Key techniques (4): -Parallel capacitor scaled delay elements form the 2 nd interpolation level Below gate delay resolution is based on parallel different delay elements < 10 ps resolution no accumulating nonlinearity

10 10 Designed 7-channel TDC TDC can measure time intervals from start to three successive pulses + Stop pulse widths in Mode 0 Slew rates of the stop pulses in Mode 1

11 11 Measurement core

12 12 Circuit architecture 0.35µm CMOS chip size 2.4mm 3.7mm

13 13 Measurement example Start pulse and 3 successive stop pulses created with signal generator measurements µ = average value σ = standard deviation value (precision)

14 14 Circuit characteristics Description Measured Value Measurement resolution (LSB) 8.88 ps, equals 1.3mm Precision (standard deviation value) 8-12 ps Measurement MHz internal ±74 µs, equals ±11 km freq. Non-linearity < ±2 ps, when range > 2 m, equals < ±0.3 mm Temperature drift <0.5 ps/ C, equals < C Output interface SPI, max clock frequency 100 MHz Timing signal inputs and other IO-signals LVCMOS compatible Supply voltage 3.3V typical ( V) Power 220 MHz 85 mw Temperature range -40 C.. 85 C Circuit dimensions 2.4 mm 3.7 mm = 8.89 mm 2 Package QFN 36

15 15 Multichannel high precision TDC Key component in reaching mm-level measurement performance in laser radars Thank you for your attention! This work has been supported by the EC within the 7th framework programme under grant agreement FP7-ICT _ (MiniFaros)