A level shifter is used in order to propagate signals through different supply voltage domains. For example, a low voltage ground-referred control signal may be converted into a high voltage signal. In automotive applications, the high supply voltage domain can have voltage levels up to 60V, while the control signal can be issued from a 3V supply voltage domain. In order to minimize power dissipation, quiescent currents and discharging capacitors are generally avoided. This is particularly relevant for applications using charge pumps or bootstrapping. Propagation delays through the level shifters should also be optimized, and the level shifters should provide failsafe start-up conditions. One of the most common level shifters is the cross-coupled level shifter. Cross-coupled level shifters have large cross conduction losses during switching events, and there is no default output state.
Turning to FIG. 1, a resistor based level shifter 100 can be seen. The level shifter 100 generally comprises resistor R1, PMOS transistor Q1, NMOS transistors Q2 and Q3, and diode D1. The resistor R1 is a pull-up resistor that is coupled to the high voltage domain, receiving high voltage level VBOOT. Transistor Q3 is coupled with its channel in series to the resistor R1, and the gate of transistor Q3 receives the low level input signal IN from the low supply voltage domain. Transistors Q1 and Q2 form an inverter in the high supply voltage domain between node N1 and the high supply voltage level VBOOT. Diode D1 is coupled between the source of transistor Q2 and node N1. The output node OUT provides the level shifted version of the input signal in the high supply voltage domain. This level shifter 100 has large quiescent current in its on-state through the resistor R1. Furthermore, the speed is limited by the large voltage swing at resistor R1. However, a small value of R provides quick turn-off. This means that the size of the resistor R provides a trade-off between quiescent current and speed.