A surgical system includes a surgical instrument having a body, a shaft extending distally from the body, an ultrasonic transducer supported by the body, and an end effector at a distal end of the shaft. The end effector includes an ultrasonic blade configured to be driven by the ultrasonic transducer with ultrasonic energy, and an RF electrode operable to seal tissue with RF energy. A generator is operatively coupled with the surgical instrument and is operable to generate a combined drive signal having an ultrasonic energy component and an RF energy component. Filter circuitry arranged externally of the body of the surgical instrument is operable to convert the combined drive signal to an ultrasonic drive signal configured to energize the ultrasonic transducer to drive the ultrasonic blade with ultrasonic energy, and an RF drive signal configured to energize the RF electrode with RF energy sufficient to seal tissue.
