In this paper, a CMOS current-mode four-phase quadrature oscillator using current differencing transconductance amplifier (CDTA)-based new first-order allpass filter is proposed. The proposed circuit structure is very simple. It contains only one resistor, two capacitors and three CDTAs. It can provide four quadrature current outputs, and the steady state oscillation is achieved after less than 1µs. Additionally, as all the output impedances of the four-phase quadrature oscillator are high, the proposed oscillator circuit can be connected directly to the next stage without any impedance matching requirements. PSPICE simulation results are included to confirm the theory.

Keywords: Allpass filter, Current mode, Current differencing transconductance amplifiers, Quadrature oscillator (QO).