A LINEARLY-TUNABLE OTA-C SINUSOIDAL OSCILLATOR FOR LOW-
Jader A. De Lima
VLSI Design & Instrumentation, Electrical Engineering Dept, Universidade Estadual Paulista
12516-410 Guaratinguetá – SP
ABSTRACT: A low-voltage, low-power OTA-C sinusoidal
oscillator based on a triode-MOSFET transconductor is here
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 VTUNE linearly adjusts the oscillation frequency.
According to a standard 0.8µm CMOS n-well process, a
prototype was integrated, with an effective area of 0.28mm2.
Experimental data validate the theoretical analysis. For a single
1.8V-supply and 100mV≤VTUNE≤250mV, the oscillation frequency
fo ranges from 0.50MHz to 1.125MHz, with a nearly constant
gain KVCO=4.16KHz/mV. Maximum output amplitude is 374mVpp
@1.12MHz. THD is -41dB @321mVpp. Maximum average
consumption is 355µW.
Sinewave voltage-controlled oscillators (VCOs) are
essential elements in many communication systems, PLLs,
instrumentation, measurements, etc. The use of battery-
driven mobile equipment has been rapidly expanded in
recent years, so that the need for low-voltage, low-power
(LVLP) oscillators has accompanied such a trend. The
linearity improvement attained by amplitude regulation is
mandatory in many applications such as on-chip filter auto-
multiplicative noise due to the VCO finite phase-noise .
In case of OTA-C oscillators, the transconductor built-in
nonlinearity has usually been used as amplitude limiter .
This work describes a sinusoidal, linearly tunable OTA-
C VCO based on a gain-boosting triode-MOSFET LV
transconductor . Owing to the operation of input
transistors on triode region, dynamic range is extended as
compared to saturated devices. Furthermore, the linear
dependence of small-signal gm on d