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    Integrable QPSK Modulator Using CMOS Technology
    (2018-08-20)
    Wongprommoon, Natapong
    ;
    Manositthichai, Narongsak
    ;
    Prommee, Pipat
    This paper presents a design of voltage-mode QPSK modulator circuit based on CMOS analog signal processing subsystems. The circuit consists of dual-output all-pass filter, analog switches and summing operator. All-pass filter is used as a phase-shifter which provides ± 90 degrees phase shifted at considered frequency. Trigonometric relationship identities are used for obtaining the completed 4-quadrant phase shifted signals. CMOS analog switches are constructed with the summing junction for obtaining the QPSK modulation signal outputs by arithmetic algorithm. All-pass filter and summing junction are realized by using CMOS-based differential voltage buffer (DVB) with a few passive elements. The results are verified by PSpice using ± 1.5V power supplies which are in agreement with the theory expectations.
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    Log-domain all-pass filter and its application to quadrature sinusoidal oscillator
    (2011-10-13)
    Prommee, Pipat
    ;
    Pattanatadapong, Thanate
    ;
    Somdunyakanok, Montri
    A realization of current-mode log-domain all-pass filter is proposed. The circuit is a direct realization of a first-order differential equation for obtaining the low-pass filter. The proposed all-pass filter is realized by using log-domain low-pass filter. The log-domain all-pass filters is realized by using only 10 NPN transistors and a grounded capacitor for achieving low-power and fast response. The frequency response and stage gain can be electronically tuned through bias currents. An application of proposed log-domain all-pass filter is a quadrature sinusoidal oscillator. The proposed oscillator is obtained by cascading two all-pass filters loop. A validated BJT model which is used in SPICE simulation operated from a single power supply as low as 2V. The proposed circuit is also suitable for high-frequency applications. SPICE simulation results confirm the theoretical results. © 2011 IEEE.