Technique for Load-Independent Millimeter-Wave Output Power Monitoring for Mass-Volume Testing

This paper presents a circuit technique for an accurate output power measurement of mm-wave power amplifiers during mass-production on-wafer testing of integrated transceivers. Basic functionality is tested in a single testbed insertion by contacting all the chip pads simultaneously using a specifically designed probe card. The output power is usually measured via power detector and monitored as a DC voltage read-out. However, the large parasitics of the probe card pins, placed at the RF pads corresponding to power amplifier output, may significantly alter the load seen by the power amplifier due to an undefined impedance and lead to a false measured power. We propose a simple circuit technique how to overcome this error and make the output power detection independent of the parasitic load seen at the RF pads. We derive a theory and verify it in simulation. For load swept over the entire Smith Chart, the absolute inaccuracy of detected power is less than 2 dB.