Temperature tracking current reference for multilevel phase-change memories

In this paper, a temperature tracking current reference for read and verify operations in multilevel phase-change memories is proposed. The circuit is able to track the temperature behavior of the PCM cell current of all programmed states over a temperature range from −20 °C to 80 °C. The proposed solution is based on an MOS transistor biased near its zero temperature coefficient point. Only room temperature trimming is required to adjust the value and the temperature behavior of the generated current. Simulated results show a good agreement with experimental data on PCM cells: the error is kept within 5% in any process condition.