Digital Oscilloscope High-frequency Active Differential Probe Design

High-bandwidth active differential probes are essential in the field testing of signal integrity in high-speed electronic systems. A significant challenge is ensuring that the probe accurately captures signals without disrupting the operational state of the circuit. This necessitates that the active probe's input port exhibits high input impedance within the passband range. However, the presence of distributed parameters in the input circuit frequently results in substantial input capacitance. In this study, we model and analyze the input network, adopting a transimpedance amplification-based input circuit and designing a compensation network to effectively reduce the input impedance of the active probe. Experimental results demonstrate that the active probe circuit achieves an input bandwidth of 5 GHz with flatness within ±2 dB and exhibits excellent phase-frequency response.