Kari Määttä

A high-precision time-to-digital converter for pulsed time-of-flight laser radar applications

A time-to-digital converter (TDC) has been designed, and six units have been constructed and tested. It consists of integrated digital time-interval measurement electronics with a /spl plusmn/10-ns resolution that can be improved to /spl plusmn/10 ps by an analog interpolation method. Identical construction of the interpolation electronics leads to stable performance of the TDC. The drifts of all six TDC units remain within /spl plusmn/10 ps over a temperature range from -10/spl deg/C to +50/spl deg/C. The stability can be improved further by a real-time calibration procedure developed here. The single-shot precision of the TDC is better than 15 ps (standard deviation), but precision can be improved to below 0.1 ps by averaging about 10 000 measurements at the maximum measurement speed of 100 kHz. The time range of the TDC is currently 2.55 /spl mu/s, but this can be increased by adding an external digital counter. The TDC suffers from a periodic nonlinearity over the measured time range from 0 to 1.3 /spl mu/s, the amplitude and period of the nonlinearity being /spl plusmn/20 ps and 40 ns, respectively. The reason lies in the integrated digital part of the electronics. The linearity of interpolation in the 10-ns time range improves, however, as more results are averaged.

Profiling of hot surfaces by pulsed time-of-flight laser range finder techniques.

The possibilities for using the pulsed time-of-flight (TOF) laser radar technique for hot refractory lining measurements are examined, and formulas are presented for calculating the background radiation collected, the achievable signal-to-noise ratio (SNR), and the measurement resolution. An experimental laser radar device is presented based on the use of a laser diode as a transmitter. Results obtained under real industrial conditions show that a SNR of 10 can be achieved at measurement distances of up to 15-20 m if the temperature of the converter is 1400 °C and the peak power of the laser diode used is 10 W. The single-shot resolution is about 60 mm (sigma value), but it can be improved to millimeter range by averaging techniques over a measurement time of 0.5 s. A commercial laser radar profiler based on the experimental laser radar device is also presented, and results obtained with it in real measurement situations are shown. These measurements indicate that it is possible to use the pulsed TOF laser radar technique in demanding measurement applications of this kind to obtain reliable data on the lining wear rate of a hot converter in a steel works.

Integrated time-of-flight laser radar

A small, hand-held pulsed time-of-flight (TOF) laser radar device has been designed and tested. The aim was to implement the receiver channel and time-to-digital converter (TDC) with application-specific integrated circuits (ASICs) in order to reduce power consumption, cost, weight, and size. The measurement range of the device is from 1 m to 30 m to a noncooperative target, and an accuracy of 35 mm is achieved with a measuring time of 200 ms between temperatures of -10/spl deg/C and +30/spl deg/C. Power consumption during continuous measurement is 0.84 W.

Binary logic operations using a beam-scanning laser diode

A beam-scanning binary logic (BSBL) and its implementation using a beam-scanning laser diode (BSLD) are proposed. The BSBL is categorized as spatial coding information processing, which operates with spatially coded light signals. A basic BSBL unit consists of two photodetectors, two amplifiers, a light source, and a beam scanner. A unit with three output photodetectors can execute eight types of binary two-inputs/one-output optical logic operations with small modifications: FALSE, AND, XOR, OR, NOR, XNOR, NAND, and TRUE.

Pulsed time-of-flight laser radar module with millimeter-level accuracy using full custom receiver and TDC ASICs

A laser rangefinding device based on a pulsed time-of-flight distance measurement technique was constructed and tested. The aim, millimeter-level measurement accuracy with low power consumption, cost, and size, were achieved using full-custom application-specific integrated circuits in significant parts of the device, the receiver channel, and the time-to-digital converter. The accuracy of the device with a measurement time of one second and of the optomechanical head used in the measurements is at the mm-level in the case of a noncooperative target at a measurement range from 4 to 34 m and at a temperature between -10/spl deg/C and +50/spl deg/C.

Wide-Range Time-to-Digital Converter With 1-ps Single-Shot Precision

A high-resolution time-to-digital converter (TDC) was designed and tested. The converter is based on the fundamental method of counting the full clock cycles of a low-phase-noise reference clock and using a single-stage interpolating method employing time-to-amplitude converters that are based on Miller integrators. Counters and other control logic were implemented on a field-programmable gate array, and the interpolation units were constructed using discrete components. The single-shot precision of the uncompensated converter is about 1.8 ps over a time interval range of 0 to 328 μs. Single-shot precision is limited by the nonlinearities of the interpolators. These measurement errors caused by the nonlinearities are systematic, and thus, precision can be improved to 1 ps by a simple integral nonlinearity compensation. Other important factors that contribute to single-shot precision are the N -cycle jitter of the reference clock and the noise generated by the TDC circuit itself. By careful design, these errors can be made small enough to achieve picosecond-level precision.

Time-To-Digital Converter For Fast, Accurate Laser Rangefinding

The construction and capability of a time-to-digital converter (TDC) intended for industrial laser rangefinding applications is described. The time interval T to be measured is split into three fractions T1, T12 and T2. T1 and T2 are the time fractions between the start pulse and the next clock pulse but one and between the stop pulse and the next clock pulse but one. T12 is thus synchronized with the clock and can be accurately digitized by a counter. The time difference Ti - T2 is digitized by an analogue interpolation circuit which consists of separate time-to-amplitude converters and A/D converters for the two time fractions. The measured time T is achieved by calculating the sum T12 + T1 - T2 and is a 16 bit digital word in which the lsb corresponds to about 40 ps. The measurement range of the TDC is 2.55 µs. The integral nonlinearity and single shot resolution were measured to be 5 ps (?-value) and 40 ps (?- value) respectively. Temperature stability is -3 ps/°C in a temperature range of 0°C - +50°C. A stability test over 14 hours indicated a peak to peak drift of about 10 ps, which includes the stabilities of the measuring instruments. The dead time of the TDC is about 10µs.

Timing discriminator for pulsed time-of-flight laser rangefinding measurements

A time-pickoff circuit based on the constant fraction discriminator (CFD) timing principle has been developed for pulsed time-of-flight laser rangefinding with pulse lengths of 5–10 ns. It is based on detection of the crossing point of the trailing edge of the original timing pulse and the leading edge of its delayed replica with a fast emitter coupled logic comparator. A simplified theory is presented here for its walk error. Three types of comparator were tested in the CFD. It is shown that the dominant source of walk error is that produced by the limited gain-bandwidth product of the comparator and that walk error can be reduced to ±1 mm in a 1:10 dynamic range of input pulses by adding an external offset voltage between the input nodes of the comparator.

Internal Q-switching in semiconductor lasers: high intensity pulses of the picosecond range and the spectral peculiarities

Optical pulses of /spl sim/100 ps duration, and /spl sim/10/sup 2/ W power were obtained from the industrial single heterostructure lasers with a standard pulse generation power of /spl sim/10 W in the internal Q-switching mode. Temporal and spectral analyses allow three components to be distinguished in the laser optical pulses: ordinary delayed pulses of large duration at energies considerably lower than the energy gap, short optical pulses caused by the gain-switching effect at higher energies, and short optical pulses at the end of the current pulse (Q-switching mode) at the highest energies. A model is proposed involving band tail states as a saturable absorber causing large delays. >

Pulsed time-of-flight laser range-finding techniques for industrial applications

Typical construction and performance data for a pulsed time-of-flight laser rangefinding device intended for industrial measurements is presented. It is shown that by using a laser diode transmitter with a peak power of 5 - 15 W, a measurement range of a few tens of meters can be attained with respect to a noncooperative target. The available single shot resolution reaches mm-level in a fraction of a second. Accuracy depends greatly on the construction and adjustment of the device and levels of better than +/- 3 mm can be achieved in the above measurement range. Various construction details and other factors affecting to the available resolution and accuracy are discussed.