A system on chip (SOC) includes a processor circuit configured to receive instruction information from an external source and to execute an instruction according to the received instruction information and a workload estimator circuit configured to monitor instruction codes executed in the processor circuit, to generate an estimate of a workload of the processor circuit based on the monitored instruction codes and to generate power supply voltage control signal based on the estimate of the workload. The SOC may further include a power management integrated circuit (PMIC) configured to receive the control signal and to adjust a power supply voltage provided to the SOC in response to the control signal.