A Technique for Differential Noise Figure Measurement of Differential LNAs

This paper presents an approach to measure the noise figure of a differential low-noise amplifier (LNA) based on familiar ldquocold-hotrdquo single-ended noise figure measurements. To demonstrate the usefulness of this approach, measurement results are presented for a wideband differential LNA designed to be used as the first stage of the receiver in the Square Kilometre Array radio telescope. The presented LNA achieves less than 0.41 dB of differential noise figure in the 700 MHz to 1.4 GHz band, differential S₁₁ <-13 dB, differential S₂₁ between 18 and 14 dB, single-ended output P1 dB of -8.2 dBm, and output IP3 of -1 dBm while consuming 81 mA from a 1.3-V supply. The approach of measuring the differential noise figure may be automated with one switch at the output of a standard noise source and one switch at the input to a standard noise figure analyzer or a noise figure meter, allowing for automated noise figure measurements of differential LNAs based on the differential pair topology.