Abstract: To detect whether a closed-loop's voltage is out of range, a voltage detector includes first and second transistors that deliver first and second currents respectively to first and second high impedance nodes. The voltage detector further includes third and fourth transistors that draw third and fourth currents respectively from the first and second nodes. The first and second currents are scaled replicas of a current flowing through a current source of a voltage-to-current converter that converts the close-loop's voltage to a current and supplies a first voltage to the first and second transistors. The third and fourth currents are scaled replicas of a different current flowing through a current mirror of the voltage-to-current converter and that supplies a second voltage to the third and fourth transistors.

Abstract: A power supply self adjusted circuit that can sense a power supply voltage and detect whether the power supply is of a first value (e.g., 5V) or a second value (e.g., 3.3 V). In the case of a modem system, the power supply self adjusted circuit then adjusts the modem system accordingly. Hence, using this circuit, a modem or other signal processing circuit can be designed to work for both 5V and 3.3V power supply systems, for example. Futhermore, the power supply self adjusted circuit enables a modem system to automatically adjust itself when the power supply is switched from 5V to 3.3V or vice versa, without any manual intervention from the user. This capability is important for increasingly-popular PC Card- modems.