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    Synthesis of electronically tunable multifunction biquad filter using voltage differencing differential input buffered amplifiers
    (2025-02-01)
    Bunrueangsak, Sirigul
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    Biquad filters are commonly used in analog circuits for various purposes in signal processing and communication applications. We synthesize an analog active biquad filter with five types of voltage-mode filtering functions. The filter is synthesized using a parallel passive resistor-inductor-capacitor (RLC) network and unity-gain voltage differencing amplifier. A voltage differencing differential input buffered amplifier (VD-DIBA) is the main active component, and the biquad filter has a three-input single-output (TISO) topology. By replacing the passive inductor and resistor with VD-DIBA-based inductance and resistance simulators with a subtractor, the TISO voltage-mode versatile filter is obtained from two VD-DIBAs, one resistor, and two capacitors connected to the ground. The proposed filter can provide five types of voltage-mode filtering functions: inverting bandpass and lowpass responses as well as noninverting band-stop, high-pass, and all-pass responses. The all-pass filter requires no additional active components. The three input voltage nodes have high impedance, and a low-impedance output voltage node facilitates cascade connections without using additional voltage buffers. In addition, the natural frequency and quality factor can be electronically tuned. The quality factor is controlled without disturbing the passband gain and natural frequency. The proposed filter is simulated and verified experimentally in the Personal Simulation Program with Integrated Circuit Emphasis (PSPICE) and through laboratory tests employing VD-DIBAs implemented using commercially available components.
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    Single Active Element Based Electronically Controllable Capacitance Multiplier
    (2022-07-15) ;
    Huaihongthong, Pintira
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    ; ;
    The realization of capacitance multiplier using the versatile active building block, namely voltage differencing differential difference amplifier (VDDDA) is presented in this paper. The realized capacitance multiplier is very simple consisting of one VDDDA, one MOS resistor (RM) and one grounded capacitor which is attractive for integration. The multiplication factor (KC) of the realized circuit can be electronically controlled via the bias current (IB) and control voltage (VC) without the need of any matching condition of active and passive element. Moreover, the multiplication factor can be adjusted to be more or less than one. The performances of the presented capacitance multiplier are verified through Pspice simulation using CMOS VDDDA in 0.18μm TSMC technology with ±0.9V power supplies. The multiplication factor is designed to be KC=2 by choosing VC=0.85V, IB=50μA and C=30 pF. The simulated multiplication factor is around 1.98. The simulated operational frequency range is around three decades (6.16 kHz-8.91MHz). The performances of the proposed circuit are also verified by the experiment using VDDDA implemented from the commercial ICs, AD830 and LM13700 with ±5V power supplies. The experiment is conducted under the same multiplication factor (KC=2) as the simulation by choosing RM=0.27 kω (1% passive resistor), IB=96.2μA and C=1nF. The experimental multiplication factor is around 2.06. The experimental operational frequency range is around three decades (1kHz-1.25MHz). By adjusting the bias current from 17.67μA to 400 μA, the experimental multiplication factor is controllable from 11.47 to 0.48. The percent deviation of the theoretical and experimental multiplication factor is lower than 5% when the value of bias current is greater than 39μA. These deviations stem from the effect of the parasitic capacitance and resistance in VDDDA. Moreover, the application example of the presented capacitance multiplier as the sinusoidal oscillator is presented. The performances of the presented oscillator verified via the experiment are well consistent with theoretical anticipation.
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    Electronically and orthogonally tunable sito voltage-mode multifunction biquad filter using lt1228s
    (2021-10-27)
    Wai, May Phu Pwint
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    The commercially available IC LT1228 is an interesting active device due to its advantage features, such as a fast transconductance amplifier, a wide bandwidth over a wide range of voltage gain, low total harmonic distortion (THD), high impedance differential input, etc. The single-input triple-output (SITO) voltage-mode (VM) multifunction biquadratic filters using ICs, LT1228s are introduced in this research. This circuit design provides the three-filtering functions, low-pass (LP), high-pass (HP), and band-pass (BP), without changing the circuit architecture. It comprises three LT1228s, four resistors, and two capacitors connected to the ground. The low impedance voltage output nodes are HP and BP responses. The quality factor (Q) and the pole frequency (ω0) can be electronically and orthogonally tuned by altering the third LT1228's bias current (IB). The PSPICE simulation and the experiment are verified to describe the circuit operation.
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    Single commercially available ic-based electronically controllable voltage-mode first-order multifunction filter with complete standard functions and low output impedance
    (2021-11-01) ;
    Buakhong, Unchittha
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    Khateb, Fabian
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    Sotner, Roman
    This paper presents the design of a voltage-mode three-input single-output multifunction first-order filter employing commercially available LT1228 IC for easy verification of the proposed circuit by laboratory measurements. The proposed filter is very simple, consisting of a single LT1228 as an active device with two resistors and one capacitor. The output voltage node is low impedance, resulting in an easy cascade-ability with other voltage-mode configurations. The proposed filter provides four filter responses: low-pass filter (LP), high-pass filter (HP), inverting all-pass filter (AP−), and non-inverting all-pass filter (AP+) in the same circuit configuration. The selection of output filter responses can be conducted without additional inverting or double gains, which is easy to be controlled by the digital method. The control of pole frequency and phase response can be conducted electronically through the bias current (I<inf>B</inf>). The matching condition during tuning the phase response with constant voltage gain is not required. Moreover, the pass-band voltage gain of the LP and HP functions can be controlled by adjusting the value of resistors without affecting the pole frequency and phase response. Additionally, the phase responses of the AP filters can be selected as both lagging or leading phase responses. The parasitic effects on the filtering performances were also analyzed and studied. The performances of the proposed filter were simulated and experimented with a ±5 V voltage supply. For the AP+ experimental result, the leading phase response for 1 kHz to 1 MHz frequency changed from 180 to 0 degrees. For the AP− experimental result, the lagging phase response for 1 kHz to 1 MHz frequency changed from 0 to −180 degrees. The design of the quadrature oscillator based on the proposed first-order filter is also included as an application example.
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    A New Method to Synthesise the Sinusoidal Oscillator Based on Series Negative Resistance-Capacitance and its Implementation Using a Single Commercial IC, LT1228
    (2023-01-01)
    Kulapong, Worawut
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    Sotner, Roman
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    An alternative method for synthesising the sinusoidal oscillator based on series negative resistance-capacitance is presented in this paper. The proposed topology is constructed with the series negative resistance-capacitance circuit connected in parallel with a grounded resistor and capacitor. To validate the proposed method, a new grounded series negative resistance-capacitance simulator is also proposed as a subcircuit for synthesising the sinusoidal oscillator. The series negative resistance-capacitance simulator is based on a commercially available integrated circuit (IC), LT1228. The equivalent negative resistance and equivalent negative capacitance can be adjusted electronically using an external DC bias current. The sinusoidal oscillator that is synthesised using the proposed method consists of a single LT1228, two capacitors, and three resistors. The frequency and the condition of the oscillation are orthogonally adjusted. Also, the condition of oscillation is electronically controlled. The amplitude of the sinusoidal waveform is adjustable. In addition, the output voltage node of the proposed oscillator has a low impedance, which allows it to connect to other circuits without using an additional buffer. Both PSPICE simulation and experiment are used to validate the proposed circuits.
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    Reconfigurable Voltage-Mode First-Order Multifunction Filter Employing Second-Generation Voltage Conveyor (VCII) With Complete Standard Functions and Electronically Controllable Modification
    (2023-01-01) ;
    Sangyaem, Surasak
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    Khateb, Fabian
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    Minaei, Shahram
    In this contribution, the realization of a first-order, two-input, single-output voltage-mode multifunction filter employing a second-generation voltage conveyor (VCII) is described. The proposed first-order versatile filter is extremely simple, composed of a single VCII and three passive devices. Because of its low output impedance, the output voltage node can be easily cascaded with other voltage-mode configurations without the requirement of any buffers. In the same circuit topology, the proposed first-order filter provides various filtering functions: inverting and non-inverting low-pass (LPF), inverting and non-inverting high-pass (HPF), as well as inverting and non-inverting all-pass (APF). The digital method allows the selection of output first-order filtering functions without the need for additional circuits such as inverting or double-gain amplifiers. Furthermore, the pass-band gain of the low-pass and high-pass responses can be adjusted by varying the resistance or capacitance values without influencing the pole frequency as well as the phase response. The influence of VCII's current/voltage gain errors and parasitic elements on filtering performance is also investigated. Moreover, the modification of the proposed lagging phase all-pass filter to achieve electronic controllability is also proposed by replacing the passive resistor with the operational transconductance amplifier (OTA). The 0.18μm TSMC CMOS structure of the VCII employed in the proposed filter operates in the subthreshold region and utilizes the bulk-driven technique (BD), enabling it to operate with 0.4V supply voltage and consuming 383 nW of power. The total harmonic distortion (THD) of the LPF with an applied input voltage Vinpp=300 mV @ 50Hz is -49.5 dB. An application example as a quadrature sinusoidal oscillator realized from the proposed first-order allpass filter and lossless integrator is also included. The performance of the proposed reconfigurable voltage-mode first-order filter is simulated and experimentally tested using a commercially available AD844 IC-based VCII with ±5 V power supply.
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    Voltage-Controlled Sinusoidal Oscillator Using Commercially Available ICs with Amplitude Adjustability and Its Application to FM and FSK Modulations for Transmission and Processing of Identified Low-Frequency Signals
    (2026-04-01) ; ; ;
    Sotner, Roman
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    Nramat, Wichai
    This paper presents a new voltage-controlled sinusoidal oscillator employing only two commercially available LT1228 integrated circuits, four resistors, and two capacitors. The proposed oscillator provides independent control of oscillation frequency and oscillation condition, as well as adjustable output amplitude, while maintaining low output impedance without requiring additional active components. The oscillation frequency is electronically and linearly tuned via the LT1228 bias current or control voltage. Experimental results confirm the practicality of the design: The proposed VCO achieves a wide linear tuning range from 9.25 kHz to 837.2 kHz, THD below 2.55%, and phase noise of –73.35 dBc/Hz at a 1 kHz offset for a 237.8 kHz carrier. The amplitude of the sinusoidal output is adjustable from 0.48 Vp-p to 6.64 Vp-p. In addition, the proposed VCO is successfully applied to FM and FSK modulation for low-frequency signal transmission, and the FM demodulation test yields a recovered sawtooth signal with an SNR of 34.51 dB. Compared with existing LT1228-based oscillators, the proposed circuit achieves 25% lower power consumption (149 mW) and reduces the number of ICs required while improving functional versatility. These results validate the effectiveness and novelty of the proposed LT1228-based design.
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    Single VDDDA-Based Lossy Inductance Simulator for Application to Sinusoidal Oscillator
    (2023-01-01) ; ;
    Sotner, Roman
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    This work presents the design of a new grounded lossy inductance simulator. The proposed circuit emulates an inductor in parallel with a negative resistor, making it applicable to the design of a sinusoidal oscillator. The proposed simulator comprises a voltage differencing differential difference amplifier (VDDDA), a resistor, and a grounded capacitor. The proposed active inductor necessitates no essential matching criteria for passive elements. The equivalent inductance and negative resistance can be controlled electronically. Moreover, the parallel RLC and negative resistance configuration-based sinusoidal oscillator is designed as an example of its application. The oscillation frequency and condition are adjusted orthogonally. The performance of the proposed simulator circuit and the sinusoidal oscillator is evaluated using Pspice simulation and experimentation with VDDDA built from ICs AD830 and LM13700. The simulation and experimental results validate the behavior of the theory.
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    Electronically Tunable TISO Voltage-Mode Universal Filter Using Two LT1228s
    (2022-01-01)
    Wai, May Phu Pwint
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    ; ; ;
    This study aims to design an electronically tunable voltage-mode (VM) universal filter utilizing commercially available LT1228 integrated circuits (ICs) with three-input and single-output (TISO) configuration. With the procedure based on two integrator loop filtering structures, the proposed filter consists of two LT1228s, four resistors, and two grounded capacitors. It realizes five filter output responses: low-pass, all-pass, band-reject, band-pass, and high-pass functions. By selecting input voltage signals, each output responses can be achieved without changing the circuit architecture. The natural angular frequency can be controlled electronically. The input voltage nodes Vin1 and Vin3 possess high impedance. The output node has low impedance, so it can be cascaded to other circuits. The performance of the proposed filter is corroborated by PSpice simulation and hardware implementation which support the theoretical assumptions. The result shows that the range of total harmonic distortion (THD) is lower than 1%, and that the higher the temperature is, the lower the natural angular frequency is.
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    Current/voltage controlled quadrature sinusoidal oscillators for phase sensitive detection using commercially available IC
    This paper presents the quadrature sinusoidal oscillators for a phase sensitive detection (PSD) system. The proposed oscillators are design by using the commercially available ICs (LT1228). The core oscillator consists of three LT1228s: two grounded capacitors and one resistor. By adding four resistors without the requirement of additional active devices, the amplitudes of two quadrature waveforms become adjustable. The quadrature output nodes are of low impedance, which can be connected to the impedance sensor or other circuits in a phase sensitive detection system without the need of buffer devices. The amplitudes of the quadrature waveform are equal during the frequency of oscillation (FO) tuning. The frequency of oscillation is electronically and linearly controlled by bias current or voltage without affecting the condition of oscillation (CO). Furthermore, the condition of oscillation is electronically controlled without affecting the frequency of oscillation. The performances of the proposed oscillators are experimentally tested with ±5 voltage power supplies. The frequency of the proposed sinusoidal oscillator can be tuned from 8.21 kHz to 1117.51 kHz. The relative frequency error is lower than 3.12% and the relative phase error is lower than 2.96%. The total harmonic distortion is lower than –38 dB (1.259%). The voltage gain of the quadrature waveforms can be tuned from 1.97 to 15.92. The measurement results demonstrate that the proposed oscillators work in a wide frequency range and it is a suitable choice for an instrument-off-the-shelf device.