Fujihiko Matsumoto

Neural Network Analysis and Evaluation of the Fetal Heart Rate

The aim of the present study is to obtain a highly objective automatic fetal heart rate (FHR) diagnosis. The neural network software was composed of three layers with the back propagation, to which 8 FHR data, including sinusoidal FHR, were input and the system was educated by the data of 20 cases with a known outcome. The output was the probability of a normal, intermediate, or pathologic outcome. The neural index studied prolonged monitoring. The neonatal states and the FHR score strongly correlated with the outcome probability. The neural index diagnosis was correct. The completed software was transferred to other computers, where the system function was correct.

Evaluation of prolonged fetal monitoring with normal and pathologic outcome probabilities determined by artificial neural network

Objective: The purpose of this study was to objectively evaluate prolonged fetal heart rate (FHR) monitoring, which has been difficult to do with conventional cardiotocogram (CTG). Methods: FHR was analyzed by an artificial neural network computer that calculates probabilities of normal, pathologic and suspicious outcome. Earlier normal and pathologic outcome probabilities (OPs) recorded during 15-min intervals are averaged every 5 min. Initially, two curves (the averaged normal and pathologic OPs) are compared. Furthermore, a single curve traced for each difference between the averaged normal and pathologic OPs and its value are studied. Our FHR probability data are of 9 cases reported in a previous paper on neural network FHR analysis. Results: In the 4 cases of normal neonatal condition, the trends of the averaged curves and the last averaged values were higher for normal OP than for pathologic OP, and the final values of the difference were >0. On the other hand, in the 5 cases of neonatal depression, the trend of the two curves and the final values were lower for normal than for pathologic OP; and the final difference values of averaged probabilities were <0. For prolonged monitoring, the single parameter is more useful than the comparison of the two curves. Conclusion: A useful single parameter is obtained for the accurate and objective evaluation of prolonged FHR monitoring. The present method is promising for prospective studies using the combined system of experts and neural computers.

A high-precision low-voltage bipolar current mirror circuit and its compensation for stability

A current mirror circuit is widely utilized as an important building block in analogue signal processing circuits. This paper describes a high-precision low voltage bipolar current mirror circuit. Well known current mirror circuits, such as a simple current mirror and a Wilson current mirror, have a trade-off between low-voltage operation and accuracy of the current gain. The accuracy of the proposed current mirror is high in spite of low current amplification factor (β) of transistors and large current output (or a large number of the multiple output). The current mirror circuit can operate at a 1V or less supply voltage. The high accuracy is realized by negative current feedback with high gain. Thus, the stability of the circuit and compensation methods are discussed. PSPICE simulation shows that the proposed current mirror circuit compensated using Miller components composed of a capacitor and a resistor is stable and can operate at a 1V supply voltage.

Linear bipolar OTAs based on a triple-tail cell employing exponential circuits

Two types of new operational transconductance amplifiers (OTA), which are composed of exponential circuits and a triple-tail cell, are presented. The linear input voltage ranges of the proposed OTAs are wider than that of the triple-tail cell and have lower current consumption. The improvement of the signal-to-noise ratio is confirmed. The results of SPICE simulation show that the OTAs have good frequency responses. Monte Carlo simulation shows that the transconductance deviation of the proposed OTAs due to process variation is comparatively similar to that of the triple-tail cell.

Design of a floating-type impedance scaling circuit for large capacitances

Impedance scaling technique is known as a method to reduce chip area of large capacitances for low frequency integrated filters. The conventional technique realizes only grounded low impedance components. This paper proposes a construction of a floating-type impedance scaling circuit. The proposed circuit can be applied to various low frequency analog circuits. The validity of the proposed circuit is confirmed by simulation of a biquad filter employing the proposed circuit.

Time-Frequency Analysis of the Blood Flow Doppler Ultrasound Signal

Power spectral analysis is extensively used to interpret ultrasound data. However, the technique is useful only when the data can be treated as stationary. Ultrasound data are mostly nonstationary. Thus, a short time Fourier transform (STFT or spectrogram) is widely used to analyze spectral components which change with time. However, the STFT has a low accuracy in both time and frequency domains. Currently, Cohens class time-frequency (TF) analysis is popular for analyzing nonstationary signals. The authors recently proposed a new kernel (named a figure eight kernel). In order to apply the TF analysis with the new kernel to a blood flow signal, experimental data were obtained from the carotid artery by an ultrasound Doppler monitor (Toitsu, Japan). To analyze the data, three kernels were used: (1) a Wigner kernel, (2) a Choi-Williams kernel, and (3) a figure eight kernel. Using our new figure eight kernel, the demodulation accuracy was improved and blood flow components were observed.

A design of a low-transconductance linear transconductor utilizing body effect for low frequency applications

For medical devices, low frequency applications are required. Thus, a transconductor which has a very low transconductance is needed. A conventional low-power and low-transconductance transconductor has a problem that a linear input range is narrow for the medical use. This paper proposes an improved local-feedback MOS transconductor operating in subthreshold region utilizing body effect. The proposed transconductor is optimally designed using Newton-Raphson method and Downhill simplex method. The characteristics of the proposed transconductor are confirmed by simulation under the condition that the transconductance is lower than 1 μS. The 1% linear input range is around 100 mV. The THD is around -40 dB for the amplitude of the input voltage is 170 mV under the condition that the frequency of the sinusoidal input voltage is 100 Hz. The simulation results show validity and availability of the proposed transconductor.

A New Linear Transconductor Combining a Source Coupled Pair with a Transconductor Using Bias-Offset Technique

Linearity of a transconductor with a theoretical linear characteristic is deteriorated by mobility degradation, in practice. In this paper, a technique to improve the linearity by combining a source-coupled pair with the transconductor is proposed. The proposed transconductor is the circuit that the deteriorated linearity of the conventional part is compensated by the transconductance characteristic of the source-coupled pair. In order to confirm the validity of the proposed technique, SPICE simulation is carried out. The transconductance change ratio of the proposed technique is about 1% and is 1/10 or less of the conventional circuit.

A technique to reduce power consumption for a linear transconductor

A new method to reduce power consumption of a linear transconductor is proposed in this paper. The minimum tail current for the operation of the transconductor is supplied by a new current source circuit. The proposed circuit is based on a dynamic biasing current technique. Results of SPICE simulation show that the proposed technique is very effective to reduce power consumption of the transconductor.

Linear bipolar OTAs employing exponential‐law circuits

This paper presents design of linear bipolar OTAs, which are composed of two function blocks; one is an exponential-law circuit and the other is a core cell. Multi-tanh cells are employed as the core cell. This kind of OTA has lower power dissipation relatively to the conventional multi-tanh cell. According as the order of the multi-tanh core cell becomes higher, the number of circuit realization for the core cell increases. For example, we have two OTAs for the core circuit of an emitter-coupled pair and four OTAs for the doublet core cell. Thus, we consider the generalized OTAs for an arbitrary order n of the core cell and obtain a formula to give the realization number of the linear OTAs for n. According to the formula, there must be eight OTAs in the case of n=3. All of the eight OTAs are examined. Analysis and simulation results show that the OTAs have advantage in their characteristics, such as linear input range, power dissipation, noise, and frequency response. Copyright 2004 John Wiley & Sons, Ltd.