Amplitude-Regulated Quadrature Sine-VCO Employing an OTA-C Topology

Transconductance amplifier capacitor oscillators (TACOs) readily produce phase-shifted sinusoids with low distortion over a wide frequency range. Hence, TACOs can be used in applications including telecommunications and lock-in amplifiers. The precise amplitude regulation needed in such applications necessitates an automatic gain controller (AGC) with an envelope detector. TACOs and envelope detectors have frequency-dependent nonidealities which complicate AGC design and incite amplitude modulation outside a limited frequency range. This brief presents a VCO with an AGC that uses maxima sampling to compensate for envelope detector nonidealities. The VCO, which is evaluated using a field-programmable analog array, is tunable from 30 Hz to 40 kHz and consumes
$\leq $
50
$\mu \text{W}$
.