A linearly-tunable OTA-C sinusoidal oscillator for low-voltage applications

A low-voltage, low-power OTA-C sinusoidal oscillator based on a triode-MOSFET transconductor is discussed. The classical quadrature model is employed and the transconductor inherent nonlinear characteristic with input voltage is used as the amplitude-stabilization element. An external bias V_TUNE linearly adjusts the oscillation frequency. Using a standard 0.8 μm CMOS n-well process, a prototype was integrated, with an effective area of 0.28 mm². Experimental data validated the theoretical analysis. For a single 1.8 V-supply and 100 mV≤V_TUNE≤250 mV, the oscillation frequency f_o ranges from 0.50 MHz to 1.125 MHz, with a nearly constant gain K_VCO=4.16 kHz/mV. Maximum output amplitude is 374 mV_pp @ 1.12 MHz. THD is -41 dB @ 321 mV_pp. Maximum average consumption is 355 μW.