Apparatus and methods for quadrature clock signal generation are provided. In certain implementations, an apparatus includes an invertible sine shaping filter configured to receive an in-phase clock signal, a quadrature-phase clock signal, and an inversion control signal. The invertible sine-shaping filter is further configured to filter the in-phase and quadrature-phase clock signals to generate sinusoidal in-phase and quadrature-phase clock signals. The invertible sine-shaping filter is further configured to selectively invert one or both of the in-phase and quadrature-phase clock signals based on an inversion control signal. The apparatus further includes a phase interpolator configured to generate an interpolated clock signal based on a weighted sum of the selectively inverted sinusoidal in-phase clock signal and the quadrature-phase sinusoidal clock signal. The in-phase clock signal and the quadrature-phase clock signal have a quadrature-phase relationship.