Ilkka Nissinen

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

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.

Integrated Receiver Including Both Receiver Channel and TDC for a Pulsed Time-of-Flight Laser Rangefinder With cm-Level Accuracy

An integrated receiver that includes both the time-to-digital converter (TDC) and the receiver channel and is intended for a pulsed time-of-flight laser rangefinder with a measurement range of approximately 10 m has been designed and fabricated in a standard 0.13 mum CMOS process. The receiver operates by detecting the current pulse of an optical detector and producing a stop timing mark for the TDC by means of a leading edge timing discriminator. The TDC is used to measure the actual time interval between the start and stop pulses and the slew-rate of the stop pulse, to compensate for a walk error produced in the discriminator. The single-shot precision of the whole receiver is 250 ps for a minimum detectable signal, and its accuracy and power consumption are plusmn 37 ps with compensation within a dynamic range of at least 1:10,000 and less than 45 mW, respectively. The size of the die is 1300 mum times1300 mum including pads.

Fluorescence suppression in Raman spectroscopy using a time-gated CMOS SPAD

A Raman spectrometer technique is described that aims at suppressing the fluorescence background typical of Raman spectra. The sample is excited with a high power (65W), short (300ps) laser pulse and the time position of each of the Raman scattered photons with respect to the excitation is measured with a CMOS SPAD detector and an accurate time-to-digital converter at each spectral point. It is shown by means of measurements performed on an olive oil sample that the fluorescence background can be greatly suppressed if the sample response is recorded only for photons coinciding with the laser pulse. A further correction in the residual fluorescence baseline can be achieved using the measured fluorescence tails at each of the spectral points.

A sub-ns time-gated CMOS single photon avalanche diode detector for Raman spectroscopy

A time-gated single photon avalanche diode (SPAD) has been designed and fabricated in a standard high voltage 0.35 μm CMOS technology for Raman spectroscopy. The sub-ns time gating window is used to suppress the fluorescence background typical of Raman studies, and also to minimize the dark count rate in order to maximize the signal-to-noise ratio of the Raman signal. The proposed time-gating technique is applied for measuring the Raman spectra of olive oil with a gate window of 300 ps, and shows significant fluorescence suppression.

On Laser Ranging Based on High-Speed/Energy Laser Diode Pulses and Single-Photon Detection Techniques

This paper discusses the construction principles and performance of a pulsed time-of-flight (TOF) laser radar based on high-speed (FWHM ~100 ps) and high-energy (~1 nJ) optical transmitter pulses produced with a specific laser diode working in an “enhanced gain-switching” regime and based on single-photon detection in the receiver. It is shown by analysis and experiments that single-shot precision at the level of 2W3 cm is achievable. The effective measurement rate can exceed 10 kHz to a noncooperative target (20% reflectivity) at a distance of > 50 m, with an effective receiver aperture size of 2.5 cm2. The effect of background illumination is analyzed. It is shown that the gating of the SPAD detector is an effective means to avoid the blocking of the receiver in a high-level background illumination case. A brief comparison with pulsed TOF laser radars employing linear detection techniques is also made.

On-Chip Voltage Reference-Based Time-to-Digital Converter for Pulsed Time-of-Flight Laser Radar Measurements

A fully integrated time-to-digital converter (TDC) for a pulsed time-of-flight laser rangefinder has been designed and fabricated by a standard 0.18-mum CMOS process. The time-to-digital conversion is realized by counting the full clock cycles of an on-chip ring oscillator between timing signals and by recording the state of its 12 phases at the moment of arrival of the timing signals and their delayed replicas. The frequency of the oscillator is stabilized to an on-chip voltage reference by means of a frequency-to-voltage-converter-based feedback loop. The resolution and single-shot precision (standard deviation) of the TDC are ~ 60 ps and less than ~ 50 ps, respectively, in a range of 80 ns. The worst-case temperature dependence of the TDC is less than 50 ppm/degC in the temperature range of 0 degC to 70 degC, corresponding to 0.6 mm/degC at a distance of 12 m (80 ns). The power consumption of the TDC is less than 18 mW.

A Multitime-Gated SPAD Line Detector for Pulsed Raman Spectroscopy

A time-gated 2 × (4) × 128 single photon avalanche diode line detector for pulsed laser Raman spectroscopy has been developed and fabricated in a 0.35-μm high-voltage CMOS technology. The sample is illuminated with short laser pulses (~100 ps) at a rate of ~50 kHz and four time gates synchronized with these pulses and having selectable widths within the subnanoseconds range are used to measure the Raman photons and fluorescence background simultaneously. The fluorescence background measurement is used to suppress the residual fluorescence level to improve the quality of the Raman spectrum. The variation in the width of the time window was measured to be approximately ±17.5 ps along the spectral axis when set externally to a nominal value of 100 ps. Measurements with a reference sample demonstrate the effect of nonhomogeneities in the time gates on the quality of the recorded Raman spectrum and the residual fluorescence correction.

A low voltage CMOS constant current-voltage reference circuit

The proposed CMOS current-voltage reference circuit consists of a traditional bandgap circuit based on the use of PMOS transistors in weak inversion. Its current is stabilized by an on-chip resistor with positive temperature coefficient. The voltage reference is produced by compensating the positive temperature coefficient of a resistor by the negative temperature coefficient of the diode connected PMOS transistor by driving the constant current of the current reference through them. The simulated temperature coefficients of the voltage and the current were less than 85 ppm//spl deg/C and 54 ppm//spl deg/C, respectively, in the worst-case simulation over the temperature range of -10/spl deg/C to 70/spl deg/C without trimming, and the supply-voltage coefficients of the voltage and current were 0.16% over the supply voltage range of 1.1 V to 2.2 V.

A 2-channel CMOS time-to-digital converter for time-of-flight laser rangefinding

A time-to-digital converter (TDC) based on a free running ring oscillator and timing signal interpolators has been fabricated in a 0.13 μm CMOS process for the receiver of a pulsed time-of-flight laser rangefinder (TOF). The time-to-digital conversion is based on counting the pulses of this eighth-stage, differential ring oscillator and additionally registering the state of its 16 phases at the arrival moment of the timing signals and their delayed replicas. The temperature and supply voltage dependences of the ring oscillator are compensated for by measuring its frequency by means of an accurate time generator. The single-shot precision standard deviation value and the nonlinearity of the TDC are less than 20 ps (3 mm) and ±16 ps (2.4 mm), respectively, in the distance range of 0 to 15 m. The power consumption is less than 16 mW.

2×(4×)128 time-gated CMOS single photon avalanche diode line detector with 100 ps resolution for Raman spectroscopy

A 2×(4×)128 multiphase time-gated single photon avalanche diode (SPAD) line detector has been designed and fabricated in a high voltage 0.35 μm CMOS technology for Raman spectroscopy. The time positions of the photons can be measured with the resolution of 100 ps using four time gates over the whole line detector simultaneously. This approach enables to reduce the fluorescence background of the Raman spectrum markedly. Measurements showed that the time gates can be distributed over the whole line detector with the accuracy of ± 35 ps which is adequate for a time-gated pulsed Raman spectroscopy using a laser pulse width of approximately 150 ps.