As the world moves towards S F6-free insulation technologies, understanding the dielectric behaviour of alternative gas mixtures is becoming increasingly important. Detailed characterization of partial discharge (PD) behaviour within conventional measurement circuits is constrained by distortion of the fast transient signal, limiting the effective measurement bandwidth. This study presents a novel measurement circuit that omits the traditional coupling capacitor and instead leverages the inherent capacitance of the gas-insulated structure to establish a more compact and sensitive detection path. The improved setup enables detailed time-domain acquisition of fast-rising PD pulses using a high-frequency current transformer (HFCT). Using this system, the corona discharge characteristics of a CO2 / O2(7 0 % / 3 0 %) gas mixture are experimentally investigated at pressures of 0.2,0.3 and 0.4 MPa. Phase-resolved PD patterns are analysed to assess the influence of gas pressure on PD inception voltage, charge magnitude, and pulse repetition behaviour.