Loopback testing of integrated circuits

Loopback testing may be provided for one or more transmission output paths of a semiconductor Integrated Circuit (IC). One or more parametric loopback sensors are provided in the semiconductor IC, each parametric loopback sensor being configured to receive a clocked data input signal to a respective transmitter of the IC and a signal from a transmission output path from the respective transmitter of the IC, and to generate a respective sensor output based on a comparison of the clocked data input signal and the signal from the transmission output path for the respective transmitter of the IC. A programmable load circuit is also provided in the semiconductor IC, coupled to each transmission output path.