Electronically Tunable Current-Mode Square-Root-Domain First Order All-Pass Filters and Their Quadrature Oscillator Applications

This paper proposes square-root-domain currentmode first order inverting and non-inverting all-pass filters. The proposed filters are designed by using state-spacesynthesis method with current-mode square-root circuits, squarer/divider circuits, current mirrors, current sources and grounded capacitors without any external resistors. Therefore, the proposed filters are appropriate to develop into an integrated circuit. The center frequency can be adjusted electronically by changing the values of the external current sources. A current-mode quadrature oscillator has been included to be an example for the practice. The proposed oscillator is obtained by cascading inverting and non-inverting all-pass filters loop. 3 Volts power supply was used to operate the all-pass filter circuits and the oscillator circuit. In order to demonstrate the performances of them, the PSPICE simulations have been provided to confirm the theoretical analyses. The filters are simulated by using TSMC 0.25 μm Level 3 CMOS process parameters for this purpose.