High Stability Voltage Controlled Current Source for Cervical Cancer Detection using Electrical Impedance Spectroscopy

The design of a High Stability Voltage Controlled Current Source (VCCS) for Cervical Cancer Detection (CCD) applying Electrical Bio-Impedance Spectroscopy (EBS) is presented. The circuit was designed and simulated in TSMC 130 nm CMOS technology at 1.3V power supply. The proposed Howland Current Source is based on Self-Biased Complementary Folded Cascode (SB-CFC) Operational Amplifier (OA). Complying with the requirements for medical electrical equipment of international standard ABNT-NBR-IEC-60601-1 the sinusoidal current peak amplitude was settled at 10 µA. In accordance with the requirements of the EBS for CCD, the specifications for the SB-CFC-OA were calculated to meet the 100 Hz to 1 MHz frequency range for the sinusoidal output current and the output impedance higher than 1 MΩ at 1 MHz frequency. Post-layout simulations were run and the main results were: 10 ± 0.0335 µA for the output current peak amplitude over the specified frequency range and with 5 kΩ load impedance; values above 1.6 MΩ output impedance @ 1 MHz; nominal current amplitude variations lower than 0.4% for load impedances in the range of 10 Ω up to 5 kΩ. From these results, the performance of the VCCS is adequate for EBS-CCD applications.