a testing circuit includes a signal generator operative to provide a control signal in response to a reference clock signal . the control signal may include both alignment and timing information operative to synchronize the timing and output of the signal generator with a device under test . a clock recovery instrument is electrically coupled to the signal generator . the clock recovery instrument generates the reference clock signal in response to a clock signal from the device under test . the reference clock signal is synchronized with the clock signal from the device under test such that signal generator operation is synchronized with the device under test independent of the behavior of the device under test .