Yoji Isota

Negative Group Delay Circuit for Feed-Forward Amplifier

We present a design and an implementation of a negative group delay circuit, which consists of lumped parameter element. It is very small and simple circuit. The circuit is composed of three resonators with resisters, which are arranged to pi type circuit to improve the reflection. We discuss the principle of a negative group delay circuit and apply the circuit to the feed-forward amplifier. It is confirmed that the delay line of the distortion cancellation loop is shortened 40% by connecting the circuit to the driver stage of the error amplifier. The efficiency of the feed-forward amplifier has been improved from 9% to 12%.

A monolithic even harmonic quadrature mixer using a balance type 90 degree phase shifter for direct conversion receivers

This paper proposes a novel circuit configuration of an even harmonic quadrature mixer (EHQMIX) for direct conversion receivers. In this EHQMIX, a 90 degree phase shifter consists of balance type high pass and low pass filters, and it does not require any circuits connecting to the ground plane. So this configuration is suitable for low cost monolithic IC without any via-holes, because amplitude and phase imbalance caused by inductance included in wires and leads of a package for circuits to the ground plane can be reduced. A developed L-band MMIC achieves good quadrature detecting characteristics.This paper proposes a novel circuit configuration of an even harmonic quadrature mixer (EHQMIX) for direct conversion receivers. In this EHQMIX, a 90 degree phase shifter consists of balance type high pass and low pass filters, and it does not require any circuits connecting to the ground plane. So this configuration is suitable for low cost monolithic IC implementation without any via-holes, because amplitude and phase imbalance, caused by the inductance included in the wires and leads of a package, can be reduced for circuits connected to the ground plane. A developed L-band MMIC achieves good quadrature detection characteristics.

A Triple-Tuned Ultra-Wideband VCO

We have already proposed a triple-tuned voltage-controlled oscillator (VCO) for achieving an ultra-wideband characteristic. The triple-tuned VCO consists of an active device and three tuned circuits. The fabricated VCO has achieved the oscillation bandwidth of 5.6-16.8 GHz and the phase noise of -114.9 dBc/Hz +/-2.9 dB at 1-MHz offset from the carrier. In this paper, for the first time, the conditions that the VCO achieves the ultra-wideband characteristic are clarified by formulation and simulation. It is also clarified that a transistor of the larger emitter size is suitable for the wideband VCO. In addition, the performances of the proposed VCO are compared with other reported wideband VCOs. As a result, it is shown that the proposed VCO has achieved the lowest figure of merit in the C-Ku-band.

Frequency and Phase Difference Control Using Fractional-

This paper proposes novel frequency and phase difference control of output signals in multiple fractional-N PLL (F-PLL) synthesizers sharing a reference signal. In the proposed F-PLL synthesizers, frequency control and phase difference control can be performed independently through cyclic shift and composition of control data of frequency dividers. The proposed synthesizers are demonstrated in the L-band, realizing highly accurate output frequency and phase difference control. The measured phase difference error from a designed value is plusmn2deg or less.

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We developed a high speed wireless LAN prototype in the 5 GHz band. Maximum transmission rate of the developed WLAN equipment was 324 Mbit/sec using 6 multi-channels of 802.11a. We proposed a novel frame aggregation scheme to improve MAC efficiency. The proposed frame aggregation scheme had a feature of an adaptive aggregation size selection depending on wireless channel conditions and application requirements. Throughput performance was simulated in the case of multiple stations with the proposed frame aggregation. The evaluated system throughput was achieved more than 150 Mbit/sec in the case of 10 STAs. It is found that throughput of the developed equipment was measured to be more than 170 Mbit/sec using the proposed frame aggregation

PLL Synthesizers by Composition of Control Data

A planar image rejection mixer (IRM) with power dividers which have phase differences is presented. The 135 and 45 deg of the phase differences give high image rejection ratio and high LO-RF port isolation. Since this IRM consists of only planar circuits without the crossover between LO and RF lines, it is suitable for discrete configuration. The fabricated IRM with 135/45 deg power dividers has achieved -20 dB of image rejection ratio and 30 dB of LO-RF port isolation over the frequency range from 1.85 GHz to 2.9 GHz.

324Mbps WLAN equipment with MAC frame aggregation

This paper proposes a design method of a Doherty amplifier, which can determine the most efficient backed-off point of the amplifier by adjusting a load modulation parameter. The parameter is defined through the design of output transmission line of a carrier and a peak amplifier using a virtual open stub technique. This paper describes the design results using the technique to optimize efficiency of a Doherty amplifier for an orthogonal frequency division multiplexing (OFDM) signal, and parameter adjustment for a linearized Doherty amplifier using an adaptive digital predistortion (ADPD). Applying this method, the developed 250W ADPD Doherty amplifier has achieved drain efficiency of 43.4% and intermodulation (IM) distortion of -48.3 dBc with output power of 44.1 dBm (10.1 dB output backed-off) at 563 MHz using an OFDM signal for integrated services digital broadcasting-terrestrial (ISDB-T).

A Planar Image Rejection Mixer with 135/45 deg Power Dividers

A highly accurate measurement method of parameters of MZ-type LN optical intensity modulators is presented. In this method, a CW optical signal is input to an optical terminal and small CW RF signal is applied to an electrode of the modulator. Then sideband levels of an output optical signal at different bias points are measured by using optical spectrum analyzer. By using 1st order sideband levels which are measured at two different bias conditions, and using a compensation method to measured levels, we can obtain accurate chirp parameter even when very small power of RF signal is applied to the modulator. In this method, the chirp parameter can be obtained in good accuracy when the input RF voltage is only 3% of the halfwave voltage.

Efficiency Enhancement of a Digital Predistortion Doherty Amplifier Transmitter Using a Virtual Open Stub Technique

A 5 GHz-band SiGe-MMIC transceiver for 324 Mbps transmission is developed. The broadband transceiver characteristics are obtained by utilizing a 5 GHz- band Q-MOD with a circular polyphase filter in the transmitter, and a broadband IFVGA and Q-MIX in the receiver. A developed SiGe-MMIC performs EVM of 3.3%rms and EVM of 5.9%rms in the transmitter and the receiver, respectively using 64-QAM OFDM signal with 120 MHz bandwidth, which corresponds to the data rate of 324 Mbps. Utilizing the developed SiGe-MMIC, the Hi-Vision streaming video data is transmitted without interruption, and is clearly projected onto the TV.

Highly accurate measurement of LN optical intensity modulators by small RF inputs

High speed wireless LAN prototype of 324 Mbit/sec has been developed. Six channel binding of 802.11 a signal on frequency domain was employed for increasing PHY data rate. Frame aggregation was employed to improve MAC-SAP throughput. Individual adaptive data rate setting on each channel, so called adaptive dynamic channel assign was implemented in order to achieve maximum MAC-SAP throughput at any channel condition. In this paper, multiple channel interleaving over all frequency channels for randomization of burst error was presented. Interleaving can be carried out over all channels or inside individual channel. Bit and packet error rate were measured using implemented WLAN equipements with/without multiple channel interleaving. It was confirmed that improvement using multiple channel interleaving were measured to be 2 dB.