Takeshi Ohbuchi

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.

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 design method of low frequency universal filter employing MOCCIIs

In this paper, a design method of a low-frequency universal current-mode filter employing second generation multiple output current conveyors with current amplification function is proposed. Low-frequency filters for biological signals need large capacitances. To realize a large apparent capacitance on a chip, the current amplification factor of the second generation multiple output current conveyors are smaller than one. SIMetrix simulation result shows that the characteristics of the proposed filter are almost the same with the conventional filter. It should be noted that the area of capacitance in the proposed circuit is only 2% in comparison with the conventional filter.

Improvement technique of tuning range for local-feedback MOS transconductor

A local-feedback transconductor (LFB OTA) is a linear OTA operating in a saturation region. In addition, the LFB OTA operating in a subthreshold region, whose transfer characteristics are expressed by a sinh function, is utilized for low-power and low-transconductance linear OTAs. However, the LFB OTA has a limit of a tuning range of a transconductance because of a local-feedback structure. To improve the tuning range, a local-feedback circuit which is composed of pMOS transistor is used for replacing the conventional one which is composed of nMOS transistor. The proposed OTA operating in the subthreshold region works as long as a reference current source circuit works. The operating current is used to tune the transconductance of the proposed OTA. The frequency characteristics, the CMRR, and the input refereed noise of the proposed OTA are almost the same as that of the conventional LFB OTA. From the Monte Carlo simulation, the sensitivity to the size mismatch of the proposed OTA is smaller than the one of the conventional LFB OTA. The validity of the proposed technique is confirmed by simulations.