Academy Professor Juha Kostamovaara and Professor Timo Rahkonen, Circuits and Systems Research Unit, Faculty of Information Technology and Electrical Engineering, University of Oulu
Background and Mission
The Circuits and Systems group consists of ~25 researchers working at the Faculty of Information technology and electrical engineering (ITEE) at the University of Oulu. Its main activity is in the field of electronic and optoelectronic circuit and system design. The main interest of the group is devoted to certain novel devices, circuit topologies and functional units, although the group is also interested in applications, especially in the field of electronic/optoelectronic measurements and telecommunications.
The main research fields are:
- time-to-digital converters and timing circuits
- generation and detection of powerful and high-speed electrical and optical pulses/transients, and the study of breakdown phenomena in semiconductors in general
- development of pulsed time-of-flight laser range finding and time-gated Raman spectrometer technologies, especially for industrial applications
- radio telecommunications, including linearization of power amplifiers, AD/DA conversion and baseband blocks, frequency synthesis.
Part of the group activities belong to the Center of Excellence in Laser Scanning Research (funded by the Academy of Finland, 2014-2019, http://www.fgi.fi/coelasr/). Also, a FiDiPro Research Fellow Dr. Vassil Palankovski is working in the group. This 3-year position is funded by TEKES.
In the following, some details and results of the work of the group are given in selected research fields.
Pulsed Time-of-Flight Systems
Solid-state 3D Imaging Using a 1nJ/100ps Laser Diode Transmitter and a Single Photon Receiver Matrix
A 3D imaging concept (Figure 1) based on pulsed time-of-flight focal plane imaging has been developed which can be tailored flexibly in terms of performance parameters such as range, image update rate, field-of-view, 2D resolution, depth accuracy, etc. according to the needs of different applications. The transmitter is based on a laser diode operating in enhanced gain-switching mode with a simple MOS/CMOS-switch current driver and capable of producing short (~100ps FWHM) high energy (up to a few nJ) pulses at a high pulsing rate. The receiver consists of 2D SPAD and TDC arrays placed on the same die, but in separate arrays. Paraxial optics can be used to illuminate the target field-of-view with the receiver placed at the focal plane of the receiver lens.
Figure 1. The solid-state 3D laser imager concept.
To validate the concept, a prototype system was developed with a bulk laser diode/MOS driver operating at a wavelength of 870nm with a pulsing rate of 100kHz as the transmitter and a single-chip 9x9 SPAD array with 10-channel TDC as the receiver.
As an example of the measured results, Figures 2(a), 2(b) and 2(c) show the 3D images of three targets placed at a distance of ~19-20m, at which the FOV of the receiver covers roughly a 27x27cm square, implying that each pixel sees an area of approximately 3x3cm. The first target (Figure 2(a)) is a white pyramid with three steps, the second (Figure 2(b)) a white paper ramp with its surface at a 60-degree angle to the optical axis, one-third of which is covered with a lower reflective material (brown carton). The third target (Figure 2(c)) is a flat plane of white paper with a cube placed on top, causing a ~3cm step. The distance for each pixel is resolved by considering 50 detections, filtering out the distribution tail hits, and averaging over the rest of the hits (~35). According to Figure 2(b), this leads to a σ value of ~20ps (~3mm in distance).
Figure 2. (a) 3D images of a pyramid with three steps, (b) a ramp, one-third of which is covered with a low reflective material (brown cardboard), (c) a white, flat plane with a cube placed on top, and (d) a color map representation of the detection probability for the ramp target.
The measurement results indicated the potential of this laser 3D imager concept as an adaptable low-cost solution for 3D imagers. So, as the next step, a 2D high-resolution 4 kilo pixel (32x128) SPAD array with 256 TDCs single-chip receiver is under development in order to have high resolution in x-y plane at the same time as z direction.
A Receiver Circuit for Pulsed 1D-, 2D- and 3D- Laser Scanning with 32x128 SPAD Matrix and 257 TDC Channels
A new integrated circuit including single-photon avalanche detector (SPAD) matrix and multi-channel time-to-digital converter (TDC) on the same die is under construction. Together they form a highly integrated receiver and measurement system for pulsed laser distance measurement and 3D scanning.
The TDC measures time intervals between electrical start and stops, which are generated optically with the photon sensitive SPAD matrix. In typical use, the photons reflected from the measurement target hit the active areas of the SPAD cells and create timing signals for the time interval measurement (stops). The reflected 2D image on the SPAD matrix together with the hit time information of every SPAD pixel offers possibilities for 3-dimensional imaging.
The TDC part has totally 257 parallel measurement channels (1 for start and 256 for stop signals). The measurement is based on a counter and stabilized delay line interpolation, which combined provide for a linear dynamic range up to 570ns and good temperature stability. The time intervals between start and multiple stops can be solved with stable ~70 ps LSB resolution. The SPAD block contains totally 4096 SPADs, which are placed to 32 rows and 128 columns. 2 rows (totally 256 SPADS) are connected to the TDC at a time so the full scan of the whole SPAD matrix takes totally 16 measurement cycles.
The circuit offers also a second operation mode, where the time interval between single electrical start and stop signals (rising edges) can be solved. In this mode the locations of both timing signals are measured 128 times with the integrated 256 TDC measurement channels. Multiple measurement provides precise final result for the measurement time interval when the individual results are averaged.
The circuit supports a “measurement window” i.e. the SPADS get loaded only after a given number of clock periods after the start pulse and respectively the SPADS can be quenched after a certain measurement range. The measurement window helps to focus the distance measurement to a certain distance which prevents false SPAD triggering in bright conditions or because of unwanted objects. The I/O pads have been removed from one side of the circuit, see Figure 3, which makes possible to put a second circuit (mirrored) in a close proximity of the first one and double the imaging resolution. 16-bit bidirectional data interface makes measurement rate up to 300 kHz possible. The 6.6mm x 5mm circuit is generated with 0.35µm HV-CMOS technology and the first tests results should be available before summer 2017.
Figure 3. SPAD/TDC receiver with 32x128/256 channels.
2D Solid State Distance Scanner Prototype
A potentially compact 2D range profiler for the profiling of non-cooperative targets with a distance range of >10 m was demonstrated.
Figure 4. A measurement setup for optical 2D profiling measurements with the pulsed time-of-flight method utilizing SPAD detectors.
Figure 5. (a) A photograph of a test measurement scene. (b) A signal strength heat map (c) Signal detection rates for the SPADs on the fourth row, used for distance mapping. (d) A 2D distance measurement result of the test measurement scene.
A previously developed compact laser diode transmitter utilizing enhanced gain switching and providing high energy (~1 nJ, 140 ps, 100 kHz) optical pulses was used. The short laser pulse length inherently leads to centimeter distance measurement precision, while the detector can be implemented as a solid-state CMOS single-photon timing detector matrix (Figure 4). The key advantage of the proposed approach is its high integration level enabling the miniaturization of the whole system into matchbox sized volume with no moving parts.
To test the operation of a wide detector matrix (to be fabricated and tested in 2017), a previously developed 9×9 detector matrix was swept mechanically to emulate and evaluate the operation of a wider 171×9 detector matrix.
The measurement result in Figure 5 demonstrates that reliable cm-precision 2-D scanning is possible to be achieved to non-cooperative objects at distances of more than 10 m with a line rate of more than 15 lines per second with a measurement field of ~45° at a lateral resolution of about 5 mrad.
1D Miniature Laser Radar
The transmitter and the receiver electronics were implemented on a single printed circuit board (PCB) of 3.5 cm by 4.0 cm in size so that the distance between the laser diode and the detector IC is ~ 20 mm. The transmitter consist of a quantum well laser diode capable of producing high power and high speed laser pulses using a relatively simple pulsing scheme of a high-speed MOS-switch driving an RLC-circuit. The wavelength of the laser diode was 810 nm and the pulsing rate 100 kHz. The detector, including the 2D 9x9 SPAD array and the 10-channel Time-to-Digital converter (TDC) circuit, is a single-chip IC manufactured in a standard 0.35 µm high voltage complementary metal-oxide-semiconductor (HV CMOS) process having the total chip dimensions of 2.5 mm x 4 mm.
Figure 6. Single photon detection based 1D laser radar.
Both the SPAD array and the TDC circuit support a time gating feature allowing photon detection only to occur within a predefined time window. The SPAD array also supports the sub-array selection feature in order to respond to the laser spot wandering effect due to paraxial optics allowing for relaxed optomechanical accuracy requirements of the laser radar system. According to the characteristic measurement results linearity is +/- 0.5 mm with a range of ~35 m to passive targets. Nine SPAD detectors' combined detection rate varies, as a function of distance, between 28% to 100%. The single-shot precision is ~ 20 mm (FWHM).
Figure 7. Detection percentages within the 9 x 9 SPAD array as a function of the distance.
The analysis and measurement results demonstrate the feasibility and the distance measurement performance of the implemented miniature 1D laser radar. This configuration enables high-speed and high-precision distance measurement results in addition to relaxed optomechanical accuracy requirements of the laser radar system. The laser diode and the receiver IC are located on a single compact PCB in the distance of ~ 20 mm from each other, thus making the overall size of the transmitter-receiver module relatively compact. Yet, regardless of the close proximity, the photon detector electronics appear, due to their digital-like nature, to be immune to the interference caused by quite significant laser diode drive current pulse.
Single Photon Avalanche Diode (SPAD) Arrays with Multi-Channel Time-to-Digital Converter for Time-Gated Raman Spectroscopy
Raman spectroscopy is based on inelastic scattering of monochromatic light produced with a CW (continuous wave) laser illuminator. Typically, the Raman spectrum is masked by a strong fluorescence background which has restricted the use of Raman spectroscopy in many potential applications. It is possible to suppress the fluorescence background markedly if intensive short laser pulses are used to illuminate the sample in such a way that the sample response is recorded only during these short pulses. The suppression is due to the fact that Raman scattering is introduced immediately after the collision between the photons and the sample material, unlike fluorescence, which is emitted after a delay characteristic to the sample. Thus, by “time-gating” the measurement for only the period of the laser pulse, most of the fluorescence is blocked out from the recorded spectrum as shown in Figure 8.
Figure 8. Principle of “the time gating”.
In our earlier research, we have shown that time-gated single photon avalanche diode (SPAD) detectors can be effectively used in Raman spectroscopy to suppress the high fluorescence background. SPAD arrays can be fabricated by using CMOS technology with the time gating electronics resulting a compact line sensor. Several versions of the time-gated SPAD arrays have been developed during the past years.
Recently simulations and measurements have been performed to study how the signal-to-noise ratio of Raman setup could be maximized when using a SPAD array with the time gating technique. The measurement setup, see Figure 9, consists of a pulsed laser, a grating, a single movable SPAD detector and a time interval measurement unit and thus accurate time domain photon distributions can be measured at every spectral point by stepping this single SPAD over the spectral range.
Figure 9. Block diagram of a time-gated Raman setup.
Figure 10 shows simulation result where the width of a time gate is swept from zero to several nanoseconds and the signal-to-noise ratio is calculated as a function of the gate width (laser pulse width was set to 200 ps). As can be seen from Figure 6 the width of the time gate has to be decreased when higher fluorescence level samples (Raman-to-fluorescence ratio decreased) are measured.
Figure 10. SNR as a function of the width of a time gate with three different Raman-to-fluorescence ratios.
The effect of the time gate width (GW) and position on the quality of Raman spectrum can be seen in Figure 11 giving results for a sesame seed oil sample.
Figure 11. Raman spectra of sesame seed oil with three different time gates.
The effect of the timing skew of the timing signals of a recently designed 16 x 256 SPAD array with a 3-bit 256-channel TDC on the signal-to-noise ratio of Raman spectra was also investigated (time gate positions and widths are not equal at every spectral point in the array). This latest SPAD array was designed so that the photon distributions in time domain could be measured with an on-chip TDC at the every spectral point. The timing skew of the signals of the TDC causes sampling error to the Raman spectrum derivation because Raman photons are not sampled equally at different spectral points. The Figure 12 shows the Raman spectra of olive oil measured by using the SPAD array and a single SPAD swept over the spectral range. The effect of the timing skew on the SNR is seen more clearly with a sample with high fluorescence background, see e.g. sesame seed oil, whose corresponding spectra are shown in Figure 13.
Figure 12. Raman spectra of olive oil measured by using a single SPAD with micro step motor and 256 SPADs.
Figure 13. Raman spectra of sesame seed oil measured by using a single SPAD with micro step motor and 256 SPADs.
In addition, a sampling error compensation method was developed and tested during the last year. This compensation method is based on the measurement of a high fluorescent reference sample and the derivation of the sampling error as a function of the spectral point based. The Raman spectrum of sesame seed oil measured using a SPAD array and utilizing this compensation method is shown in Figure 14 which clearly demonstrates the effectiveness of this method.
Figure 14. Raman spectrum of sesame seed oil measured by 256 SPAD array utilizing error compensation techniques.
Electrical Transients and Pulsed Sub-Terahertz Radiation for Imaging
Physical Principles of Avalanching BJTs Operation in Ultra-High-Voltage/High Current/High Speed Generators
Si avalanche BJT’s have been most frequently used for nanosecond pumping of pulsed laser diodes, but operation principle of Si avalanche transistors at extreme current densities and with a switching time around 2-3 ns was absent until the last decade. First reliable 1-D and 2-D description of the process we made a decade ago, while within last few years we have experimentally proved that the parameters of short-pulsing avalanche switching cannot be explained (or predicted) without consideration of fairly complicated 3-D transient phenomena. Recently, we have mainly finalized the problem in general by description of 3-D transient peculiarities during both delay and fast switching phases.
Next, the challenging task consists in physical understanding of avalanche transistor operation in kilovolt-range nanosecond/ sub-nanosecond and picosecond pulse generators utilizing Marx-bank circuit shown in Figure 15.
Figure 15. (a) Idea of the Marx bank generator: the circuit utilizes parallel charging of the capacitors followed by serial connection of the stages with the low-ohmic load resistor RL during the switching, kΩ - range resistors r are responsible for the initial charging of the capacitors; (b) Circuit used in both the experiment and the simulations. Charged to 1300V, the coaxial transmission line TL1 discharges across the circuit containing the mercury relay MR, the transmission line TL2 (connecting cable), the total parasitic inductance L1, and a FMMT415 commercial avalanche transistor chip extracted from the package. The voltage between the collector and emitter of the transistor chip is measured using an attenuating 450 Ω resistor, two 20dB/18GHz attenuators connected in series and a 30 GHz real-time oscilloscope. The experimental conditions shown in (b) correspond to a certain "typical" situation for a transistor connected in a long chain in a Marx generator.
Every year within last five decades appear several publication presenting new generators utilizing this principle, they are used in very large number of fascinating applications, but until nowadays an operating principle of a single transistor in the chain, which has emitter-base electrodes externally short-connected has been unknown. We made very important finding in this field that bipolar avalanche transistor switching with base-emitter shunted consists of two stages. The first, picosecond-range switching, initiated by high (~2.5kV/ns) voltage ramp, is caused by diode-like double avalanche injection of the electrons and holes into the n0 collector, and can provide as fast as ~20ps voltage reduction down to ~30V, but only as a transient (non-steady-state) voltage reduction, see Figure 16. This switching then provides the necessary conditions for the second (nanosecond) stage, at which transistor-like quasi-steady-state turn-on with low residual voltage is realized thanks to electron injection from the emitter. Since electron injection at short-connected base and emitter is impossible in 1-D case, understanding of the phenomenon required 2-D approach to be implemented. Low residual voltage is important for effective operation of Marx generator in the nanosecond range, while the first switching stage is of practical significance for picosecond pulse generation. These results created for the first time basis for the physical understanding of the operation of Marx-bank generator. Particularly interesting is the fact that entire emitter area operates in Marx-bank regime, unlike only emitter-base perimeter in ordinary switching mode.
Figure 16. Voltage and current waveforms corresponding to the switching transient observed in the circuit shown in Figure 23(b). (a),(b) voltages measured and simulated at the oscilloscope input (multiplied by a factor of 10) show reasonably good fit between the experiment and physics-based modeling making sure that simulated voltage and current waveforms in (c),(d) together with simulated 2-D sections of various electro-physical parameters during the transient allowed correct interpretation of complicated phenomenon to be reported.
Next very important for practice step was a suggestion of new original circuit for Marx generators improving their reliability. The main problem Marx generators application is gradual degradation, which according to our finding is caused by peculiar 3-D phenomena. We have suggested very simple circuitry-based solution for the problem, which changes drastically actual operating area inside the device thus preventing the degradation intrinsic of traditional circuit.
Figure 17. Special design of the Marx circuit (SMC) used in the experiment and simulations (unavoidable parasitic inductances are not shown in the figure, but they were used in the simulations, and a value of ~4 nH per stage provided the best fit between the simulated and measured load current waveforms). A 50Ω load was used and resistor R values in the kΩ range were selected in certain experiments as a tradeoff between high repetition rate and circuit reliability.
Figure 18. Simulated total current density for transistor number 4 (Q4) at the instant approximately corresponding to the peak in the load current. (a)-contour cross-section at transient time 4.82 ns for SMC. (b)-current density profile along the horizontal (X) cutline at longitudinal coordinate Y=10 µm in (a). (c)-contour cross-section at transient time 5.11 ns for traditional Marx circuit (TMC). (d)-horizontal cutline at longitudinal coordinate Y= 10 µm in (c). The absolute values of the peak current density for (d) are 40, 1888 A/cm2, and 736 kA/cm2 for curves 1, 2, and 3, respectively. In the SMC the current is confined near the emitter-base perimeter (which intersects the image cross-section in two places), while in the TMC the filamentary zone is located in the middle of the emitter area at equal distances from the e-b interfaces (with externally shortened e-b contacts).
Figure 19. Temporal profiles of maximum temperature at the hottest points of each of the four transistors (Q1-Q4) in the TMC (Q1T-Q4T) and SMC (Q1S-Q4S). Although the difference in peak temperature between transistors Q2T-Q4T is not large, the hottest one is transistor Q2T, which correlates with our previous empirical statistics for transistor failures in TMCs. The difference in peak temperatures was originally caused by the difference in the voltage ramps applied to the various stages, a point to be explained in detail elsewhere. The reason why the very small difference of ~3K observed in the modeling for second and third transistor can be so important is discussed.
A special designed SMC circuit (Figure 17) was investigated experimentally and numerically by comparing with TMC circuit (base-emitter short-connected), in order to protect the transistors, especially the one in second stage, from thermal destruction due to current filamentation in TMC by means of an intrinsic base triggering of all the stages in SMC. The entire emitter-base perimeter in the SMC participates in switching, whereas in a TMC the switching is initiated across the entire area of the emitter but then changes to current filamentation due to certain 3-D transient effects (Figure 18). Very significant difference in local transient overheating in the transistors operating in TMC and SMC determines the difference in reliability of those two pulse generators (Figure 19). This new understanding points additionally to ways of optimizing the design of the transistors to be used in a Marx circuit.
This research is at its early phase, and it promises (i) very important understanding to be achieved in optimal circuitry and optimal transistor chip selection for high-speed, high-voltage generators; (ii) physical interpretation of picosecond high-voltage switching, which problem remains still an open question; (iii) paves way for the development of unique microwave emitters is sub-cm wavelength range generating high-power picosecond pulses using commercial BJTs.
Sub-THz Pulsed Emitters for Imaging
Most challenging and principally important is ongoing research and development in the field of unique pulsed sub-THz emitters suggested and realized by our group and active sub-THz imaging providing record sub-picosecond precision.
The work continues in two main directions. One is aiming at deep physical understanding of new phenomenon, which we found not long ago and termed “collapsing field domains”. This new knowledge allows us developing new versions of the emitter with main target of increasing the peak power in the generated pulses in multi-mW range, increase the emission spectrum towards 300-500GHz, and further improving the switching stability in the picosecond-subpicosecond range.
The second direction is making demonstrators utilizing as a heart the system newly developed emitters for various industrial (non-destructive tests, quality monitoring in production lines) and biomedical (cancer tissue contrast in fresh slices of breast tumor utilizing both attenuation and time-domain imaging) applications for on-site use in the operation rooms. Development of this diagnostic method can improve reliability of the diagnoses made during the operation and prevent necessity of secondary operation after time-consuming histology is ready. An example of transmission sub-THz images in amplitude and propagation delay modes for a breast-tumor sample are shown in Figure 20. These images show exact correlation of the archived imaging contrast with the position and boundaries of the cancer area. Time-domain image with sub-ps temporal precision intrinsic of our technology gives much more advanced spatial resolution and appears to be more reliable than traditional amplitude-based method.
Figure 20. (a)- fresh slice of breast-cancer tissue of 300 um in thickness; (b)- sub-THz transmission image with amplitude contrast; (c)- sub-THz transmission image with propagation delay contrast;(d)- the same as (c) in 3-D presentation, entire delay range between red and blue levels is 2 ps.
This activity was supported within last decade by Finnish Academy projects, and recently finalized TEKES MIWIN project. Two FET (Horizon) project applications have been applied, and currently very intensive work is underway on EU INFRAINNOV-01-2017 project application in large THz European consortium. At the same time, active search and negotiations are underway with companies, which may become manufacturers and/or end-users of the systems under development by our group.
Design of RF Integrated Circuits
T. Rahkonen started co-operation with Prof. Pärssinen at CWC-RT group, related to circuit development for 5G beam-steering radio integrated circuits. Rahkonen is the co-supervisor of several doctoral students employed at CWC, and has a small group in CAS group as well. The design of a prototype IC was started in late 2015, and taped out in March 2016. It includes two 15 GHz transceivers, each having four TX and four RX paths for beam-steering. A Cartesian vector modulator at RF was used to provide simultaneous phase and amplitude control for the individual paths. The chip was designed using a 45 nm CMOS SOI process.
Dr. Janne Aikio designed a stacked PA stage to increase the voltage output capability and output power. Special care was taken to study the heat transfer on a flip-chip SOI IC. Dr. Olli Kursu designed the interface circuitry for programming the 700+ control bits used to tune the biases, gains, resonance center frequencies etc. Rest of the circuit blocks were designed by the doctoral students a CWC-RT group (co-supervised by Prof. Rahkonen).
The chip was received in September, and was flip-chipped on a test PCB, and cooled from the back-side. Higher-than-expected losses caused some problems in the waking-up of the chip, but all the blocks were found to be functional. Performance measurements continued in 2017.
Doctoral student Nuutti Tervo made an interesting preliminary study on how non-linear distortion behaves in jointly linearized beam-forming transmitters. It appears that over-the-air combining can steer non-linear distortion partially to different direction than the desired linear signal.
Doctoral student Jia Sun studied the possibilities of using passive charge re-distribution and open-loop charge injection in speeding up the settling of switched capacitor circuits.
Doctoral student Christian Schuss wrote his manuscript for doctoral thesis on ways to improve the harvesting efficiency of photovoltaic solar panels. The main result is a simple method of detecting defects in PV panels, based on external biasng and using an IR-camera. The method was reported in IEEE Trans on Instr. and Meas paper listed below, and the manuscript of the thesis passed the pre-examination during the autumn.
Lanz, Brigitte (2016) Compact current pulse-pumped GaAs–AlGaAs laser diode structures for generating high peak-power (1–50 watt) picosecond-range single optical pulses. Acta Universitatis Ouluensis, Technica C 583.
senior research fellows
other research staff
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Academy of Finland
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E.A. Avrutin, N.Dogru, B.S.Ryvkin, J.T.Kostamovaara, “Spectral control of Asymmetric-waveguide Large Signal Modulated Diode Lasers for Nonlinear Applications”, IET Optoelectronics, Volume: 10, Issue: 2, 2016, Pages: 57 - 65
T. Rojalin, L. Kurki, T. Laaksonen, T. Viitala, J. Kostamovaara, K. C. Gordond, S. Wachsmann-Hogiub, C. J. Strachan and M. Yliperttula, “Fluorescence-suppressed time-resolved Raman spectroscopy of pharmaceuticals using complementary metal-oxide semiconductor (CMOS) single-photon avalanche diode (SPAD) detector.”, Analytical and Bioanalytical Chemistry, doi:10.1007/s00216-015-9156-6, First online: 09 November 2015, 14 p.
J. Nissinen, J. Kostamovaara, “A High Repetition Rate CMOS Driver for High Energy Sub-ns Laser Pulse Generation in SPAD-Based Time-of-Flight Range Finding”, IEEE Sensors Journal, Volume: 16, Issue: 6, Pages: 1628 - 1633, 2016.
J. Huikari, E. Avrutin, B. Ryvkin, J. Kostamovaara, ”High-energy sub-nanosecond optical pulse generation with a semiconductor laser diode for pulsed TOF laser ranging utilizing the single photon detection approach”, Optical Review, Vol. 23, No. 3, pp. 522 – 528, 2016
Vainshtein, Sergey N.; Duan, Guoyong; Filimonov, Alexey; Kostamovaara, Juha, “Switching Mechanisms Triggered by a Collector Voltage Ramp in Avalanche Transistors with Short-Connected Base and Emitter”, IEEE Transactions on Electron Devices, June 2016 Year: 2016, Volume: 63, Issue: 8, Pages: 3044 - 3048
S. Jahromi, J-P. Jansson and J. Kostamovaara,”Solid-state 3D imaging using a 1nJ/100ps laser diode transmitter and a single photon receiver matrix”, Optics Express, Vol. 24, No. 19, Sep 2016, 15 pages
S. Kurtti, J. Nissinen, J. Kostamovaara, “A Wide Dynamic Range CMOS Laser Radar Receiver with a Time-Domain Walk Error Compensation Scheme”, accepted to IEEE Transactions on Circuits and Systems I in 2016, 1 p., DOI: 10.1109/TCSI.2016.2619762
I. Nissinen, J. Nissinen, P. Keränen, J. Kostamovaara, “On the effects of the time gate position and width on the signal-to-noise ratio for detection of Raman spectrum in a time-gated CMOS single photon avalanche diode based sensor”, Sensors & Actuators: B. Chemical in 2016, Volume 241, 31 March 2017, Pages 1145-1152
J. Holma, I. Nissinen, J. Nissinen, J. Kostamovaara, “Characterization of the Timing Homogeneity in a CMOS SPAD Array Designed for Time-Gated Raman Spectroscopy”, accepted to IEEE Transactions on Instrumentations and Measurement in 2016
B.S. Ryvkin, E.A. Avrutin, J.E.K. Kostamovaara, J.T. Kostamovaara, “Laser diode structures with a satura-ble absorber for high-energy picosecond optical pulse generation by combined gain-and Q-switching”, Semiconductor Science and technology, 32, 025015, 2016, 8p.
G. Duan, S.N. Vainshtein, J. Kostamovaara,”Modified High-power Nanosecond Marx Generator Prevents Destructive Current Filamentation”, accepted to IEEE Transactions on Power Electronics in 2016, DOI: 10.1109/TPEL.2016.2632974, 6p.
C. Schuss et al., "Detecting Defects in Photovoltaic Cells and Panels and Evaluating the Impact on Output Performances," in IEEE Transactions on Instrumentation and Measurement, vol. 65, no. 5, pp. 1108-1119, May 2016.
N. Tervo, J. Aikio, T. Tuovinen, T. Rahkonen and A. Paerssinen, "Effects of PA Nonlinearity and Dynamic Range in Spatially Multiplexed Precoded MIMO Systems," European Wireless 2016; 22th European Wireless Conference, Oulu, Finland, 2016, pp. 1-6.
Last updated: 20.9.2017