An accurate self-bias threshold voltage extractor using differential difference feedback amplifier

A novel self-biasing MOSFET threshold voltage (V_TH) extractor circuit is presented. It implements the most popular industrial extraction algorithm of biasing a saturated MOSFET to the linear portion of its √(I_D) versus V_GS characteristic, and extrapolating the tangential line to V_GS axis. The proposed circuit performs both tasks automatically in continuous time regardless of the dimensions and technology of the device under test. A simple feedback loop utilizing a differential difference amplifier (DDA) accomplishes auto biasing, while another DDA calculates the extrapolated value. The circuit is applicable to both NMOS and PMOS devices. The paper presents the proposed extraction concept, describes the technique and circuit architecture, and verifies functionality by comparing simulated results with graphically extracted values