In this paper, we have shown the design of a wideband operation On-chip Network Analyzer (OCNA) in 45nm CMOS. Its maximum operation ranges from 0.6 ∼ 3.6 GHz with maximum phase resolution of 0.3 degree, and maximum power consumption of 3.2 mW/GHz in Cadence Spectre circuit simulation. The OCNA effective area is 0.072 mm2 which is the smallest compared to previous research group. The OCNA performance is assess by monitoring the Circuit-under-Test (CUT) frequency characteristics. The proposed OCNA successfully captures the waveform and also the CUT frequency characteristic.