Stability Study of a Broadband Current Source for Electrical Impedance Tomography

ABSTRACT This study investigates external compensation strategies to improve stability and bandwidth of an inverting negative dual configuration (INDC) Howland current source for electrical impedance tomography (EIT) applications. Fifteen compensation schemes were simulated and experimentally tested for an INDC Howland topology designed to output 100–350 μA across resistive (100 Ω–20 kΩ) and complex (parallel RC) loads. Performance was evaluated based on phase margin, AC peaking, flatness, percent error, and −3‐dB bandwidth across 100 Hz–20 MHz. The six best performing topologies were identified and underwent the full analysis. The best performing design incorporates Miller compensation capacitors at three locations ( C f− , C f+ , C g ) with a 5 MHz pole frequency. Simulations demonstrated −3‐dB bandwidth ≥ 1 MHz for loads ≤ 15 kΩ, with a phase margin ≥ 60° at 1 MHz for all loads. Experimentally, −3‐dB bandwidth ≥ 1 MHz was maintained up to 3 kΩ, with a phase margin ≥ 60° at 1 MHz for all loads. Compared with previous literature, our design achieved a > 2× improvement in flatness experimentally (1.86% vs. 4% up to 1 MHz) and extended stable operation to higher frequencies and larger load ranges. External compensation methods improve performance and stability beyond what internal op‐amp compensation alone achieves. Performance advantages were validated across a broader frequency and load range than previous INDC Howland implementations. This work establishes a systematic framework for examining broadband current sources for EIT, enabling accurate, stable current injection across clinically relevant impedance ranges and frequencies up to 1 MHz.