This paper describes amplification with improved linearity by employing a linearizing circuit in an input circuit of an internally-matched Ku-band high power amplifier. The linearizing circuit is composed of series L, C, R and an FET with grounded source and drain, and is connected between the input signal line and ground. This linearizing circuit was applied to a Ku-band 10 W output power amplifier utilizing a 25.2 mm gate-width double-doped Heterojunction FET. The power amplifier demonstrated a 8 dB reduction of the third-order intermodulation at about 6 dB output power backoff point from the 2 dB output compression point.

This paper presents a novel distortion compensation technique using an active inductor. First, we describe the input-reflection-coefficient characteristics of a GaAs MESFET active inductor when input power increases. We show that the inductor exhibits positive amplitude deviation and negative/positive phase deviation as the input power increases when the biases of the FETs are set appropriately. The chip size of the fabricated active inductor is less than 0.52 mm2. Then, we show that third-order intermodulation is improved when the active inductor is used as a predistortion linearizer. Third-order intermodulation was improved over the output range from 14 dBm to 25 dBm, and at the output of 15 dBm, third-order intermodulation was improved approximately by 9 dB when the predistortion linearizer was introduced. The active inductor can thus function as a miniaturized predistortion linearizer by using it in the input matching circuit of a power amplifier. This technique can be applied in the miniaturization of wireless communication devices.

An optical receiver with a saturated electrical amplifier is studied for signal light that is distorted due to the use of a gain-saturated semiconductor optical amplifier or homowavelength crosstalk light. It is shown that less penalty is induced in a receiver with a DC-coupled saturated amplifier than in one with a linear amplifier, in a practical situation where the decision threshold is fixed at a value optimized for a back-to-back signal. The result suggests that a receiver with a saturated amplifier or a limitter is preferable to an automatic gain control circuit for detecting distorted signal lights.

A computational cost reduction scheme for a post-distortion type nonlinear distortion compensator of OFDM signals is proposed, and compared with the conventional sub-optimum detection scheme. The proposed scheme utilizes the principle that a complex OFDM signal can be demodulated with not only both I-phase (real part) and Q-phase (imaginary part) components, but also either of them. Usually each phase of an OFDM signal exhibits different signal envelope and they are distorted differently by the nonlinearity of a power amplifier. Consequently, three output sequence patterns can be obtained at the receiver. By comparing these outputs, we can know the erroneous positions of these sequences to some extent. By the aid of this comparison, we need to evaluate only a limited number of replicas for the compensation process of the post-distortion type nonlinear distortion compensator, which results in the computational cost reduction. We have proposed four new compensation schemes based on this idea and derived their performance in terms of the bit error rate and the average number of calculations.

We propose a method of reducing laser-clipping-induced distortion in a subcarrier multiplexed (SCM) optical-cable TV system. This scheme reduces amplitude peaks of the SCM signal by controlling the phases of video carriers to prevent the clipping which occurs when these peaks fall below the threshold of a laser-diode. It is experimentally shown that using this method reduces the bit error rate in an AM-VSB / QAM hybrid optical-transmission system.

In this paper, we discuss the error correcting capability of the constant amplitude coding. In orthogonal multi-code CDMA systems, the transmitted signal has large amplitude fluctuation and the amplitude fluctuation causes large nonlinear distortion. In order to avoid the amplitude fluctuation, we have proposed "constant amplitude coding" in our previous study. The constant amplitude coding can achieve constant amplitude transmission by utilizing the redundancy of the coding, i. e. , the coding can have an error correcting effect. In this paper, we examine the effectiveness of the error correcting capability of the constant amplitude coding and show that the constant amplitude coding is very effective against nonlinear distortion under the consideration of the error correcting capability.

It becomes essential in practice to improve a processing rate and to divide an image into small segments adjusting a limited memory, because image filing systems handle large images up to A1 size. This paper proposes a new method of an automatic skew normalization, comprising a high-speed skew detection and a distortion-free dividing rotation. We have evaluated the proposed method from the viewpoints of the processing rate and the accuracy for typed documents. As results, the processing rate is 2. 9 times faster than that of a conventional method. A practical processing rate for A1 size documents can be achieved under the condition that the accuracy of a normalized angle is controlled within 0. 3 degrees. Especially, the rotation with dividing can have no error angle, even when the A1 size documents is divided into 200 segments, whereas the conventional method cause the error angle of 1. 68 degrees.

This paper discusses a design technique for multidimensional (M-D) multirate filters which cause no checkerboard distortion. In the first part of this paper, a necessary and sufficient condition for M-D multirate filters to be checkerboard-distortion-free is derived in the frequency domain. Then, in the second part, this result is applied to a scanning line conversion system for television signals. To confirm the effectiveness of the derived condition, band-limiting filters with and without considering the condition are designed, and the results by these filters are compared. A reducibility of the number of delay elements in such a system is also considered to derive efficient implementation.

A GaAs power amplifier IC has been developed for 1. 9-GHz digital mobile communication applications, such as the handsets of the Japanese personal handy phone system (PHS), which was assembled into a very small 0. 012-cc surface mount plastic package. This power amplifier using refractory WNx/W self-aligned gate MESFETs with p-pocket layers can operate with high efficiency and low distortion with a single 3-V supply. A very low dissipated current of 119 mA was obtained with an output power of 21. 1 dBm and a low 600-kHz adjacent channel leakage power (ACP) of -63 dBc for π/4-shifted quadrature phase shift keying (QPSK) modulated input.

A high power amplifier module has been developed for large cell base station in digital cordless system. For PHS application, this module exhibited Pout of 38 dBm with low ACP of -72 dBc (at 600 kHz offset point) and a power gain of 33 dB at a supply voltage of 9 V and a frequency range of 1890-1923 MHz. In order to realize this ultra low distortion performance, power FETs have been designed as considering high breakdown voltage and thermal stability. Power divider/combiner circuits, which have the advantages of low transmission loss and a function of controlling second harmonic, have been introduced. Moreover, a novel module package with features of low cost and good processing precision has been proposed.

Two approaches to the design of resonant-type switches with low distortion characteristics operating at a 2-V power supply voltage have been proposed for use in the 1. 9-GHz-band personal handy phone system (PHS). One approach is to use three stacked FETs at the receiver side. They are composed of a dual-gate FET and a single-gate FET. An insertion loss of 0. 41 dB and an isolation of 44. 0 dB were obtained at 1. 9 GHz. A third-order distortion value of -52 dBc was achieved at 19 dBm output power. Another approach is to insert a capacitor in the resonator. A third-order distortion of -49 dBc at 19-dBm output power when two stacked FETs were used at the receiver side. The layout area of the resonator is drastically reduced as compared with the above-mentioned case.

A GaAs power MESFET amplifier with a low-distortion, 10-dB gain-variable attenuator has been developed for 1. 9-GHz Japanese personal handy phone system (PHS). Independently of its gain, a very low 600-kHz adjacent channel leakage power (ACP) with sufficient output power was attained. In single low 2. 4-V supply operation, an output power of 21. 1 dBm, a low dissipated current of 157 mA and a high power-added efficiency (PAE) of 37. 2% were obtained with an ACP of -55 dBc.

This paper proposes a new nonlinear distortion compensation scheme for orthogonal multi-carrier modulation systems. Multi-carrier modulation is an effective technique for high speed digital transmission over time-dispersive channels, however, it is very sensitive to nonlinear distortion. The proposed scheme compensates for the performance degradation due to nonlinear distortion using the maximum likelihood (ML) detection criterion. While the ideal ML receiver requires a huge computational cost and is not feasible, the proposed decision algorithm can effectively reduce the computational cost. Instead of evaluating the likelihood function for all the possible sequences, the proposed scheme examines the sequences which differ by only one bit from the sequence decoded by the conventional receiver. Computer simulation results show that the proposed scheme can effectively compensate for the nonlinear distortion.

Since an orthogonal multi-carrier signal has large peak power, intermodulation distortion occurs due to the non-linearity of the power amplifier. This distortion severely deteriorates the performance of the multi-carrier system. Especially when carriers are modulated by information bits which produce the same phase shift or the alternative phase shift, the modulated signal has maximum peak power at the input of the amplifier. In order to avoid these phase shifts (code sequences), we propose a code reversal technique which suppresses the maximum peak power of multi-carrier signals for intermodulation compensation. This method utilizes the reversal codes which are added to the original information bits. We also show the effectiveness of the code reversal technique combined with error correction coding and examine the optimum operating point of the amplifier.

The redundancy of universal lossy data compression for discrete memoryless sources is considered in terms of type and d-ball covering. It is shown that there exists a universal d-semifaithful code whose rate redundancy is upper bounded by (A-1/2)n-1ln n+o(n-1ln n), where A is the cardinality of source alphabet and n is the block length of the code. This new bound is tighter than known ones, and moreover, it turns out to be the attainable minimum of the universal coding proposed by Davisson.

Let {Xk}k=- be a stationary and ergodic information source, where each Xk takes values in a standard alphabet A with a distance function d: A A [0, ) defined on it. For each sample sequence X = (, x-1, x0, x1, ) and D > 0 let the approximate D-match recurrence time be defined by Rn (x, D) = min {m n: dn (Xn1, Xm+nm+1) D}, where Xji denotes the string xixi+1 xj and dn: An An [0, ) is a metric of An induced by d for each n. Let R (D) be the rate distortion function of the source {Xk}k=- relative to the fidelity criterion {dn}. Then it is shown that lim supn-1/n log Rn (X, D) R (D/2) a. s.

Microcellular radio direct-sequence code division multiple access (DC-CDMA) system using optical link to connect their base stations to a central station is a solution of cost-effective and efficient spectrum reuse to meet the growing demand for mobile communications. In addition to the inherent multiuser interference (MUI) of CDMA signals, the system capacity is significantly reduced by a nonlinear distortion (NLD) due to the nonlinearity of optical link. In this paper, a two-stage cancellation technique is introduced into the system to cancel both the MUI and the NLD. It is performed at the receiver of the central station where the random ingredients of all user signals are estimated, and the MUI and the NLD are rebuilt and removed from the received signal. The validity of the cancellation technique is theoretically analyzed and shown by the numerical results. The analytical method and its results are also applicable to other general nonlinear CDMA.

A modified frequency domain method for analyzing nonlinear waveform distortion in a magnetic recording process is presented. The measurement technique combines a 5th harmonic measurement technique, which uses a specific 30-bit pattern including dibits, and a precompensation technique for the dibits. The 5th harmonic voltage ratio given by the former technique includes the amount of NLTS (Nonlinear transition shift) and PE (Partial erasure) in dibits. The latter precompensation technique is employed to evaluate the PE as the minimum in the 5th harmonic voltage ratio. The true NLTS can be estimated from the amount of distortion and the evaluated PE. The high accuracy of the technique was confirmed by an examination using a pulse pattern generator with varied phase and amplitude. Finally, the effects of medium properties such as coercivity and squareness on the nonlinear distortions have been investigated by applying the technique to particulate flexible media. The NLTS increased with squareness from 3.5% to 7% while PE was less than 6% for any squareness at a recording density of 76 kFRPI. When coercivity became large, NLTS and PE decreased. The direction of NLTS for Ba-ferrite media agreed with that for a perpendicular Co-Cr thin-film medium.

A new Neural Network Equalizer (NNE), employing multilayer feedforward neural network, is proposed as a compensation method for nonlinear and multipath distortion that arises from FTTA (Fiber To The Air) system. If a signal in a channel is affected by nonlinear distortion, the conventional Decision Feedback Equalizer (DFE) finds difficulty in perfect compensation of it. To compensate for nonlinear distortion as well as multipath distortion, an equalizer, employing neural network, is investigated. A new neural network equalizer, yielding a cubic function as unit output function, is proposed in order to compensate the nonlinear distortion effectively. We also propose an initial weights of neural network for preventing from local minimum. Computer simulation results show that the compensation performance of the new NNE is superior to the conventional DFE and the conventional NNE.

Characteristics of a distortion, gain and efficiency of a power amplifier grow worse extremely by different phases of the load reflection coefficient when load impedances of the power amplifier are far from 50 Ω. It was found that the value of the distortion, gain and efficiency showed the tradeoff behavior when the phase of the reflection coefficient was different in 180 degrees. Therefore we have proposed new two- and four-parallel unit power amplifiers combined in 90 degree and 45 degree different phases each in order to accomplish low distortion and high efficiency in wide range of load impedances without an isolator. We studied the power amplifiers by simulation based on experiments and realized an amplifier in that adjacent channel leakage power of π/4-DQPSK modulation (for Japan's digital cellular system) is less than -45 dBc and efficiency is over 45% in range of load VSWR less than 3.