Log-Domain all-pass filter and its application to Quadrature Sinusoidal Oscillator

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.