We propose a new sampling method for 2D and 3D implicit surfaces. The method is based on a stochastic process defined by the Langevin equation with a Gaussian random-force term. Our Langevin equation describes a stochastic-dynamical particle, which develops in time confined around the sampled implicit surface with small width. Its numerically generated solutions can be easily moved onto the surface strictly with very few iteration of the Newton correction. The method is robust in a sense that an arbitrary number of sample points can be obtained starting from one simple initial condition. It is because (1) the time development of the stochastic-dynamical particle does not terminate even when it reaches the sampled implicit surface, and (2) there is non-zero transition probability from one disconnected component to another. The method works very well for implicit surfaces which are complicated topologically, mathematically, and/or in shape. It also has some advantageous features in rendering 3D implicit surfaces. Many examples of applying our sampling method to real 2D and 3D implicit surfaces are presented.

An RF IC for a 1.1-V VHF paging receiver is developed. In order to reduce the number of components, it employs direct-conversion frequency shift keying (FSK) architecture. The RF IC adopts two new gain control circuits so as to achieve a wide input dynamic range with only a 1.1 V power supply. One is a low-voltage, low-noise, low-distortion RF amplifier and the other is a low-voltage AGC amplifier. By applying these new circuit technologies, the RF IC achieves a voltage gain of 50.5 dB and a noise figure of 4.3 dB with only 2.0 mW power consumption. Overall, the paging receiver achieves a high sensitivity of -130 dBm and low-intermodulation sensitivity of -37 dBm with bit error rate of 310-2. This paper describes the new high-frequency low-voltage circuit technologies applied in the RF IC.

Recent progress on photonic crystal fibers is reviewed aiming at their application to high performance networks. A photonic crystal fiber has an array of air holes surrounding the silica core region. Light is confined to the core by the refractive index difference between the core and the array of air holes. Photonic crystal fibers have special characteristics compared with conventional single mode fibers. One is that the dispersion characteristics can be designed. Another characteristic, that strong birefringence can be established by sizing and/or arranging the air holes, is expected to realize a polarization maintaining fiber with high birefringence of the order of 110-3. This paper will describe the characteristics of dispersion controlled PCFs and polarization maintaining PCFs that include supercontinuum generation and absolute single polarization characteristics for various types of optical devices in high performance network systems.

Substrate noise coupling in RF receiver front-end circuitry for LTE wireless communication was examined by full-chip level simulation and on-chip measurements, with a demonstrator built in a 65nm CMOS technology. A CMOS digital noise emulator injects high-order harmonic noises in a silicon substrate and induces in-band spurious tones in an RF receiver on the same chip through substrate noise interference. A complete simulation flow of full-chip level substrate noise coupling uses a decoupled modeling approach, where substrate noise waveforms drawn with a unified package-chip model of noise source circuits are given to mixed-level simulation of RF chains as noise sensitive circuits. The distribution of substrate noise in a chip and the attenuation with distance are simulated and compared with the measurements. The interference of substrate noise at the 17th harmonics of 124.8MHz — the operating frequency of the CMOS noise emulator creates spurious tones in the communication bandwidth at 2.1GHz.

For future adaptive networking services, it will be effective if autonomous agents utilize widely spread information that continuously changes. A communication network should provide a framework for agents to utilize information in a large-scale network and should positively support communications among agents. This paper proposes EcAgent (Environment for Communities of Agents). EcAgent provides agents with access to communities that are loose collections of agents. It gathers global information about communications among all agents and makes the agents share it in communities. It makes possible adaptive networking services that use various types of information. We implemented the EcAgent execution environment and some experimental applications to make an adaptive networking service. We also implemented a simulation system to evaluate how accurately the library recognized the embedded relationships as communities. The results of experiments show that the proposed methods for community recognition work efficiently.

The Fifth-Generation new radio (5G NR) services that started in 2020 in Japan use a higher peak-to-average power ratio (PAPR) of a modulated signal with a maximum bandwidth of up to 100MHz and support multi-input/multi-output (MIMO) systems even in mobile handsets, compared to the Third-Generation (3G) and/or Fourth-Generation (4G) handsets. The 5G NR requires wideband operation for power amplifiers (PAs) used in handsets under a high PAPR signal condition. The 5G NR also requires a number of operating bands for the handsets. These requirements often cause significand degradation of the PA efficiency, consequently. The degradation is due to wideband and/or high PAPR operation as well as additional front-end loss between a PA and an antenna. Thus, the use of an efficiency enhancement technique is indispensable to 5G NR handset PAs. An envelope tracking (ET) is one of the most effective ways to improve the PA efficiency in the handsets. This paper gives recent progress in ET power amplifiers (ETPAs) followed by a brief introduction of ET techniques. The introduction describes a basic operation for an ET modulator that is a key component in the ET techniques and then gives a description of some kinds of ET modulators. In addition, as an example of a 5G NR ETPA, the latest experimental results for a 5G ETPA prototype are demonstrated while comparing overall efficiency of the ET modulator and PA in the ET mode with that in the average power tracking (APT) mode.

In mobile phone systems, the 4th generation is widely prevailing in 2017, and in 2020, it is expected that the 5th generation (5G) will start to prevail. In both generations, a linear power amplifier (PA) is used. In case of 4G, in addition, such as the envelope tracking (ET) and the digital predistortion (DPD) systems are applied to improve efficiency and linearity. In case of 5G, because of wider modulation band width and parallel operation under the multiple-input and multiple output (MIMO) mode, it might be difficult to apply all systems as those of 4G. Therefore linear PA for 5G will require higher performance with standalone operation. The linear amplifier, in spite of its name, operates non-linearly. In this paper, the non-linear operations of the linear amplifier and their effects on the linearity characteristics are reviewed. After that, impacts of non-linear elements of a hetero junction bipolar transistor (HBT), by analyzing single stage amplifier, are stated. In addition, major PA architectures including ET and DPD systems are reviewed.

Matching circuits using LC elements are widely applied to high-frequency circuits such as power amplifier (PA) and low-noise amplifier (LNA). For determining matching condition of multi-stage matching circuits, this paper shows that any multi-stage LC-Ladder matching circuit with resistive termination can be decomposed to the extended L-type matching circuits with resistive termination containing negative elements where the analytical solution exists. The matching conditions of each extended L-type matching circuit are obtained easily from the termination resistances and the design frequency. By synthesizing these simple analysis solutions, it is possible to systematically determine the solution even in a large number of stages (high order) matching circuits.

This paper describes recent technology trend of mixed analog digital RF circuits. With the progress of CMOS technology, large-scale digital signal process and control function can be integrated in an RF integrated circuit and some analog signal process blocks can be translated to digital signal processing units. At the same time, the design of remaining analog functional blocks becomes very hard. In this paper, those integration techniques for receiver and transmitter in these 20 years are reviewed. As a typical example of digital assisted systems, synthesizer based transmitters are discussed in detail.

Mobile phone systems continue to evolve from the 2nd generation, which began in the early 1990s, to the 5th generation, which is now in service. Along with this evolution, the power amplifier (PA) is also evolved. The characteristics required for PA are changing with each generation. In this paper, we will give an overview of the evolution of PAs from the 2nd generation mobile phones such as GSM (global system for mobile communications) to the 5th generation mobile phones that is often called NR (new radio), in particular, the circuit system. Specifically, the following five items will be described. (1) Ramp-up and ramp-down power control circuit corresponding to GSM, (2) Self-bias circuit technology for improving linearity that becomes important after W-CDMA (wideband code division multiple access), (3) Power mode switching methods for improving efficiency at low output power, (4) Power combining methods that have become important since LTE (long term evolution), and (5) Backoff efficiency improvement methods represented by ET (envelop tracking) and Doherty PA.

As a mobile phone progresses with the third, fourth, and fifth generations, the frequency bands used in mobile phones are increasing dramatically. RF components for mobile phone terminals correspond to this increasing frequency band. In the case of power amplifier (PA), which is one of the RF components, it is necessary to correspond many frequency bands in one PA. In this case, the wideband of the matching circuit is a typical one of the technical problems of PA. In this study, we focus on two-stage and three-stage connections of LC ladder matching circuits widely applied in PA, and compare them from the viewpoint of broadband. In order to efficiently analyze multi-stage LC-matching circuits, the following two new methods were devised. First, we derived the analysis formula of LC and CL-matching circuits when the termination impedance was extended to a complex number. Second, we derived a condition in which the frequency derivative of the input impedance is zero.

We describe the first highly nonlinear dispersion-flattened polarization-maintaining photonic crystal fiber designed for nonlinear optics applications in the 1.55 µm region. The nonlinear coefficient of the fiber is 19 (W-1km-1), which is ten times that of dispersion shifted fiber. The chromatic dispersion and dispersion slope of the fiber at 1.55 µm are -0.23 ps/km/nm and 0.01 ps/km/nm2, respectively. We demonstrate the generation of a supercontinuum using the photonic crystal fiber. A symmetrical supercontinuum over 40 nm is obtained by injecting 1562 nm, 2.2 ps, and 40 GHz optical pulses into the 200 m-long photonic crystal fiber.

The paper clarifies the bifurcation mechanism responsible for a repeated appearance of period-one attractors in an R-L-Diode circuit driven by a sinusoidal voltage source E sin 2πft. Extensive measurements are performed to observe bifurcation diagrams in the f-E parameter space. After several simplifications of the dynamics, exact bifurcation equations are derived and analyzed. A major finding is that all the period-one attractors of our interest belong to the same family in the f-E parameter-space.

Since 2020, the service of the 5th generation (5G) mobile phone has been started. In order to increase the transmission speed in 5G mobile phones, the multi-level of the modulated signal is advanced, and for that, the power amplifier (PA) high linearity is required even at low output power. In accordance with this, the review of the linearization technology of a PA has become important. As a performance index of the distortion of the PA, the output power dependence of the gain and phase, the AM (Amplitude Modulation)-AM/PM (Phase Modulation) characteristic is well known. There has been a lot of consideration for the AM-AM/PM characteristics of PA. The AM-AM/PM characteristics are affected by both source and load impedances. In this paper, a single-stage HBT (Hetero-junction Bipolar Transistor) PA is described by a simple linear equivalent circuit with multiple parameter sets. Each parameter set is defined according to the PA output power level. With this simple model, we investigated the change of AM-AM/PM characteristics when the reactance parts of source and load impedances was changed. It has become clear that change in the AM-AM/PM characteristics of the PA when the parameters were changed was mainly due to the change in the AM-AM/PM characteristics at the base node.

L-type LC/CL matching circuits are well known for their simple analytical solutions and have been applied to many radio-frequency (RF) circuits. When actually constructing a circuit, parasitic elements are added to inductors and capacitors. Therefore, each L and C element has a self-resonant frequency, which affects the characteristics of the matching circuit. In this paper, the parallel parasitic capacitance to the inductor and the series parasitic inductor to the capacitance are taken up as parasitic elements, and the details of the effects of the self-resonant frequency of each element on the S11, voltage standing wave ratio (VSWR) and S21 characteristics are reported. When a parasitic element is added, each characteristic basically tends to deteriorate as the self-resonant frequency decreases. However, as an interesting feature, we found that the combination of resonant frequencies determines the VSWR and passband characteristics, regardless of whether it is the inductor or the capacitor.

This paper describes a 270-MHz CMOS quadrature modulator (QMOD) for a global system for mobile communications (GSM) transmitter. QMOD consists of two attenuators and two doubly-balanced modulators (DBM's) and fabricated by using 0.35-µm CMOS process. The carrier leakage level of -35.7 dBc and the image rejection level of -45.1 dBc are achieved. It's total chip area is 880 µm550 µm and it consumes 1.0 mA with 3.0 V power supply.

Fan-in/fan-out devices are necessary for the construction of multi-core fiber communication systems. A fan-out device using a capillary is proposed and made by connecting a tapered fiber bundle and a multi-core fiber. The tapered fiber bundle is elongated so that the core arrangement and the mode field diameter (MFD) of single-core fibers agree with those of the multi-core fiber. Suppressing the MFD change is necessary to reduce the coupling loss of the fan-out device. While elongating the fiber bundle, the MFD decreases at the beginning until the core reaches a certain core diameter, and then it begins to increase. We suppress the MFD change of the fan-out device by using this phenomenon. The average insertion loss at both ends of a multi-core fiber was approximately 1.6dB when the fabricated fan-in/fan-out devices were connected to the multi-core fiber.

Today, pedestrian navigation systems for mobile phones use 2-dimensional maps as a navigation media in general. But 3-dimensional maps or scenery images are easier to understand for users than 2-dimensional maps. To use 3-dimensional maps or scenery guidance, the measuring accuracy of user position is essential to understand guidance images. In this paper, we will present a pedestrian navigation system using real scenery photographs as a navigation media, and based on experiments we will report the evaluation result of influence of positioning accuracy on the understandability of navigation. It is shown that 3 meters or less error of positioning is tolerable for pedestrian navigation systems using scenery images.

When confirming the ACLR (adjacent channel leakage power ratio), which are representative indicators of distortion in the design of PA (power amplifier), it is well known how to calculate the AM-AM/PM characteristics of PA, input time series data of modulated signals, and analyze the output by Fourier analysis. In 5G (5th generation) mobile phones, not only QPSK (quadrature phase shift keying) modulation but also 16QAM (quadrature modulation), 64QAM, and 256QAM are becoming more multivalued as modulation signals. In addition, the modulation band may exceed 100MHz, and the amount of time series data increases, and the increase in calculation time becomes a problem. In order to shorten the calculation time, calculating the total amount of distortion generated by PA from the probability density of the modulation signal and the AM (amplitude modulation)-AM/PM (phase modulation) characteristics of PA is considered. For the AM-AM characteristics of PA, in this paper, IMD3 (inter modulation distortion 3) obtained from probability density and IMD3 by Fourier analysis, which are often used so long, are compared. As a result, it was confirmed that the result of probability density analysis is similar to that of Fourier analysis, when the nonlinearity is somewhat small. In addition, the agreement between the proposed method and the conventional method was confirmed with an error of about 2.0dB of ACLR using the modulation waves with a bandwidth of 5MHz, RB (resource block) being 25, and QPSK modulation.