A system and method for testing the conformance of a universal serial bus system to a set of predefined USB Specifications. The circuit includes a transistor, a current source, an input capacitor, an upper switch, a lower switch, a first switch, a second switch and a third switch. A quadrature phase shifter receives the local clock and a second multiplier receives the output from the power amplifier and an output from the phase shifter to provide a quadrature signal.