We review some usual laser range finding techniques for in- dustrial applications. After outlining the basic principles of triangulation and time of flight (pulsed, phase-shift and frequency modulated continu- ous wave (FMCW)), we discuss their respective fundamental limitations. Selected examples of traditional and new applications are also briefly presented. © 2001 Society of Photo-Optical Instrumentation Engineers.

Laser ranging: a critical review of usual techniques for distance measurement

This paper presents the design of a coarse-fine time-to-digital converter (TDC) that amplifies a time residue to improve time resolution, similar to a coarse-fine analog-to-digital converter (ADC). A new digital circuit has been developed to amplify the time residue with a higher gain (>16) and larger range (>80 ps) than existing solutions do. However, adapting the conventional coarse-fine architecture from ADCs is not an appropriate solution for TDCs: input time cannot be stored, and the gain of a time amplifier (TA) cannot be controlled precisely. This paper proposes a new coarse-fine TDC architecture by using an array of time amplifiers and two identical fine TDCs that compensate for the variation of the TA gain during the conversion process. The measured DNL and INL are plusmn0.8 LSB and plusmn3 LSB, respectively, with a value of 1.25 ps per 1 LSB, while the standard deviation of output code for constant inputs remains below 1 LSB across the TDC range. Although the nonlinearity is larger than 1 LSB, using an INL lookup table or better matched delays in the coarse TDC delay chain will improve the linearity further.

A 9 b, 1.25 ps Resolution Coarse–Fine Time-to-Digital Converter in 90 nm CMOS that Amplifies a Time Residue

This paper is a review of methods and techniques used for precise measurement of time intervals (TIs) or precise conversion of TIs to digital data. The following methods are described: the counter method and averaging, time stretching, time-to-amplitude conversion followed by analogue-to-digital conversion, the Vernier method, conversion utilizing tapped delay lines, and interpolation methods. Special attention has been paid to converters utilizing integrated delay lines for digital conversion of TIs, including designs with phase-locked loop and delay-locked loop circuits. This review is illustrated by design examples and contains a comprehensive list of references.

https://iopscience.iop.org/article/10.1088/0026-1394/41/1/004/pdf

Review of methods for time interval measurements with picosecond resolution

IEEE International Solid-State Circuits Conference

We propose and demonstrate a 20-ps time-to-digital converter (TDC) realized in 90-nm digital CMOS. It is used as a phase/frequency detector and charge pump replacement in an all-digital phase-locked loop for a fully-compliant Global System for Mobile Communications (GSM) transceiver. The TDC core is based on a pseudodifferential digital architecture that makes it insensitive to nMOS and pMOS transistor mismatches. The time conversion resolution is equal to an inverter propagation delay, which is the finest logic-level regenerative timing in CMOS. The TDC is self calibrating with the estimation accuracy better than 1%. It additionally serves as a CMOS process strength estimator for analog circuits in this large system-on-chip. Measured integral nonlinearity is 0.7 least significant bits. The TDC consumes 5.3 mA raw and 1.3 mA with power management from a 1.3-V supply.

1.3 V 20 ps time-to-digital converter for frequency synthesis in 90-nm CMOS

A high-precision CMOS time-to-digital converter IC has been designed. Time interval measurement is based on a counter and two-level interpolation realized with stabilized delay lines. Reference recycling in the delay line improves the integral nonlinearity of the interpolator and enables the use of a low frequency reference clock. Multi-level interpolation reduces the number of delay elements and registers and lowers the power consumption. The load capacitor scaled parallel structure in the delay line permits very high resolution. An INL look-up table reduces the effect of the remaining nonlinearity. The digitizer measures time intervals from 0 to 204 /spl mu/s with 8.1 ps rms single-shot precision. The resolution of 12.2 ps from a 5-MHz external reference clock is divided by means of only 20 delay elements.

A CMOS time-to-digital converter with better than 10 ps single-shot precision

This paper describes a time-to-digital converter (TDC) with ~1.2 ps resolution and ~327 mus dynamic range suitable for laser range-finding application for example. The resolution of ~1.2 ps is achieved with interpolation based on a cyclic time domain successive approximation (CTDSA) method that resolves the time difference between two non-repetitive signals using binary search. The method utilizes a pair of digital-to-time converters (DTC), the propagation delay difference between which is implemented by digitally controlling the unit load capacitors of their delay cells, thus enabling sub-gate delay timing resolution. The rms single-shot precision, i.e., standard deviation sigma-value of the TDC is 3.2 ps, which is achieved by using an external integral nonlinearity look-up table (INL-LUT) for the interpolators. The power consumption is 33 mW at 100 MHz with a 3.3 V operating voltage. The prototypes were fabricated in a 0.35 mum CMOS process.

A CMOS Time-to-Digital Converter (TDC) Based On a Cyclic Time Domain Successive Approximation Interpolation Method

A multichannel time-to-digital converter (TDC) implemented with 0.35-μm complementary metal-oxide-semiconductor technology that uses a low-frequency crystal as reference and measures the time intervals with counter and delay line interpolation techniques is described. The multichannel measurement architecture provides information on the time intervals between several timing signals. The circuit can be used for laser time-of-flight distance measurements, e.g., where it can determine time intervals between a transmitted laser pulse and several reflected pulses and also pulsewidths or rise times, to compensate for the timing walk error. This paper shows how several measurement channels can be integrated into one TDC without losing the measurement performance. The circuit offers a measurement precision that is better than 8 ps and a measurement range of up to 74 μs. In terms of laser distance measurement, its performance is equivalent to millimeter-level precision within an 11-km range.

A Multichannel High-Precision CMOS Time-to-Digital Converter for Laser-Scanner-Based Perception Systems

An integrated ring oscillator based time-to-digital converter (TDC) for a pulsed time-of-flight laser rangefinder has been designed and tested. The time-to-digital conversion is based on counting the pulses of this eight-stage differential ring oscillator and additionally registering the state of its 16 phases at the arrival moment of the timing signals. The single-shot precision and the non-linearity of the TDC are better than 78.5ps and /spl plusmn/37ps, respectively and the current consumption of the time-to-digital converter was fabricated on the same chip with a receiver channel in a 0.35 /spl mu/m CMOS process.

A CMOS time-to-digital converter based on a ring oscillator for a laser radar

Accurate time-to-digital conversion is typically based on determining the positions of the timing signals within the period of an accurate clock with digital delay-line interpolators. In order to save circuit area and to improve single-shot precision to the picosecond level, multilevel interpolators can be used. Timing signals are generally asynchronous with respect to the main clock, and thus, in order to obtain unambiguous and errorless results, careful attention should be given to the synchronization of the timing signals and various operating blocks and to the generation of the interpolation residue between the interpolators. This paper attempts to describe these problems in detail and suggests some solutions using a time-to-digital converter architecture based on two-level interpolation as a test vehicle, which demonstrates 6-ps rms single-shot precision in a measurement range of 1 ms.

Antti Mäntyniemi

Papers

A CMOS time-to-digital converter with better than 10 ps single-shot precision

A CMOS Time-to-Digital Converter (TDC) Based On a Cyclic Time Domain Successive Approximation Interpolation Method

A Multichannel High-Precision CMOS Time-to-Digital Converter for Laser-Scanner-Based Perception Systems

A CMOS time-to-digital converter based on a ring oscillator for a laser radar

Synchronization in a Multilevel CMOS Time-to-Digital Converter