  Spin-orbit effects, inherent to electrons confined in quantum dots at a
silicon heterointerface, provide a means to control electron spin qubits
without the added complexity of on-chip, nanofabricated micromagnets or nearby
coplanar striplines. Here, we demonstrate a novel singlet-triplet qubit
operating mode that can drive qubit evolution at frequencies in excess of 200
MHz. This approach offers a means to electrically turn on and off fast control,
while providing high logic gate orthogonality and long qubit dephasing times.
We utilize this operational mode for dynamical decoupling experiments to probe
the charge noise power spectrum in a silicon metal-oxide-semiconductor double
quantum dot. In addition, we assess qubit frequency drift over longer
timescales to capture low-frequency noise. We present the charge noise power
spectral density up to 3 MHz, which exhibits a $1/f^{\alpha}$ dependence
consistent with $\alpha \sim 0.7$, over 9 orders of magnitude in noise
frequency.
