Voltage Reference Circuit with PTAT Current Compensation

The patent converts the harmful temperature dependence of MOS transistor threshold voltages into a beneficial feature by generating a PTAT current that compensates for threshold voltage variations. The circuit uses the inherent temperature sensitivity of transistor parameters to create a compensation mechanism, where the PTAT current's temperature coefficient counteracts the CTAT (complementary to absolute temperature) behavior of threshold voltages, achieving temperature-independent reference current.

The patent changes the operating parameters of MOS transistors by controlling their drain currents to specific relationships (e.g., I1/I2 ratios) and adjusting gate-source voltages to achieve equal overdrive voltages. By modifying bias conditions and current ratios, the circuit transforms temperature-sensitive parameters into temperature-stable reference currents through mathematical relationships between transistor parameters.

The patent employs feedback mechanisms where the generated PTAT current is fed back into the biasing network to automatically adjust operating points. The feedback loop ensures that despite process variations, the circuit maintains optimal bias conditions by dynamically adjusting currents and voltages based on actual transistor parameters, thereby reducing susceptibility to process variation while operating at low power.

The patent introduces dynamic biasing where currents and voltages are not fixed but adaptively adjusted based on circuit conditions. The bias currents are dynamically controlled to maintain equal overdrive voltages across transistors, and the circuit automatically adjusts operating points to optimize the trade-off between power consumption and process variation immunity, enabling low-power operation without sacrificing reliability.