Integrable QPSK Modulator Using CMOS Technology

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.