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Antenna transfer function evaluation scheme for ultra wideband medical applications
(2011-12-01)
Koonchiang, Krisada
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Manositthichai, Narongsak
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Fongsamut, Chalermpan
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Promwong, Sathaporn
Antennas which are used to transmit and receive UWB signals must be able to accomodate its large bandwidth. Moreover, the signals should not be distorted too much when they pass through the antennas. Therefore, the transfer function of antennas should be known for the performance evaluation. Conventionally, the authors measure the transfer function of the antenna by measuring the transmission coefficient between the transmit and the receive antenna, assuming that the transmit and receive antennas are identical. In this presentation, a more accurate three-antenna method is introduced so that the transfer function of each individual antenna can be measured. By using this method, biconical antennas are tested. The results show that these transfer functions are close to each other and that the antenna can be used for UWB meadical application (UWB-MA). Friis' transmission formula in complex form to treat the UWB signals to take into account the waveform distortion due to the frequency characteristics of the antennas [1], [7]. It is noted that Friis' transmission formula is applicable only in the far field region. In wireless meadical environments, however, the distance may not satisfy the far field condition. In this paper, we discusses the antenna evaluation of the transmission properties in Fresnel region. © 2011 IEEE.
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Minimal realization for single-element-controlled sinusoidal oscillators using single current conveyor
(2010-12-01)
Fongsamut, Chalermpan
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Surakampontorn, Wanlop
Using a two-X and two-Z second-generation current conveyor (TXTZCCII) as an active building block, two new single-element-controlled sinusoidal oscillator circuits are proposed. The circuits use only the minimum passive components, two capacitors and two resistors. All proposed circuits enjoy oscillation control through a single grounded passive element(s) and independent frequency control through another grounded passive element(s). The passive and active sensitivities of all circuits are quite low. The simulation results with PSPICE are used to verify the theory. ©2010 IEEE.
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Full-wave rectifiers based on operational transconductance amplifiers
(2007-03-01)
Jongkunstidchai, Chaiwat
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Fongsamut, Chalermpan
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Kumwachara, Kiattisak
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Surakampontorn, Wanlop
The implementation of full-wave rectifiers using operational transconductance amplifiers (OTAs) as only main active circuit elements is presented in this paper. The proposed scheme makes use of the characteristic of the differential amplifier inside the OTA and avoids the use of diodes. The typical problems of the OTA circuit, the input voltage swing limitation and the temperature dependence of the OTA transconductance gain, have been improved. Simulation and experimental results demonstrate the performance of the proposed rectifier are included. © 2006 Elsevier GmbH. All rights reserved.
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Two new RC oscillators using CCIIs
(2005-12-01)
Fongsamut, Chalermpan
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Fujii, Nobuo
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Surakampontorn, Wanlop
Two new sinusoidal oscillator circuits using current conveyors are presented in this paper. The two oscillators are related to each other by the RC:CR transformation. Each oscillator consists of two positive second-generation current conveyors (CCII+) and the minimum of (four) passive elements, two capacitors and two resistors. One of the oscillators can be realized by employing grounded capacitors and is desirable for VLSI realization. The passive and active sensitivities of all circuits are quite low. The SPICE simulation and experimental works are performed to verify this theoretical prediction. © 2005 IEEE.
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The describing function method and the analysis of the magnitude stabilization phenomenon in a nonlinear OSC
(2005-12-01)
Pranayanuntana, Poramate
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Anuntahirunrat, Kongsak
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Fongsamut, Chalermpan
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Kaewsaiha, Pongrapee
We present a nonlinear analysis of a non-linear oscillator which uses an operational transconductance amplifier (OTA), a second generation current conveyor (CCII), or a current feedback operational amplifier (CFOA) as a nonlinear element. Nonlinear oscillators are nonlinear systems that can display oscillations of fixed amplitude and fixed period without external excitation. These oscillations are called limit cycles, or self-excited oscillations. The magnitude stabilization phenomenon in a nonlinear oscillator is one of the characteristics of stable limit cycles. An equivalent feedback configuration of an oscillator circuit with a nonlinear feedback element is used. The essential tool here is the describing function method used for predicting the existence of limit cycles and, more generally, used to analyze the magnitude stabilization phenomena. We motivate this method for the physical insights into the analysis and design of nonlinear oscillator circuits based on nonlinear devices such as OTA, CCII, CFOA, etc. The describing function method offers also a way for finding the magnitude of an oscillation via an integral equation. Simulation results using MATLAB and PSPICE agree well with the theory. © 2005 IEEE.
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A wide-band current-mode OTA-based analog multiplier-divider
(2003-07-14)
Kaewdang, Khanittha
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Fongsamut, Chalermpan
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Surakampontorn, Wanlop
A current-mode analog multiplier-divider circuit that realized through the use of operational transconductance amplifiers (OTAs) is proposed in this paper. The proposed scheme is realized in such a way that employs only OTAs as active circuit elements and does not require external passive circuit elements. The circuit is simple and can be easily constructed from commercially available IC. The circuit is temperature compensated and the circuit bandwidth is approximately close to the bandwidth of pnp current mirrors or f<inf>TP</inf>/2. The performance of the multiplier-divider circuit is discussed and confirmed by simulation results.
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High frequency CMOS precision full-wave rectifier circuit
(1999-12-01)
Guntapong, Rojanakorn
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Riewruja, Vanchai
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Fongsamut, Chalermpan
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Kaewpoonsuk, Anucha
A CMOS integrable circuit technique for the realization of full-wave precision rectifier circuit, which operates throughout in the current domain, is presented. The circuit achieves a wide dynamic range and a wide-band capability. The rectifying characteristic of the circuit exhibits a low distortion in the output signal at low level input signal, Simulation results demonstrating the circuit performance are included.

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