Reference voltage shifter

A reference voltage generator for producing a second reference voltage that is a preselected amount below a power supply voltage, the reference voltage generator comprising:

• a ground node having a ground potential thereon;
• a power supply node having the power supply voltage thereon;
• a reference voltage source producing a first reference voltage that is VREF above the ground potential;
• a first load device coupled to the ground node and generating an internal reference signal that is determined by the magnitude of current flowing in the first load device;
• a differential amplifier having a first input coupled to the first reference voltage, a second input coupled to the internal reference signal, and an output generating a signal determined by a difference between the signals on the first and second inputs;
• a current regulating switch having a control node coupled to the differential amplifier output, and coupled to determine the current through the first load device;
• and
• a second load device coupled in series with the first load device and coupled to the power supply node, wherein the second load device has an impedance selected to cause the second load device to generate the second reference voltage wherein the second reference voltage is a preselected amount below the power supply potential.

A method for generating a desired voltage from a supplied voltage comprising:

• providing a reference voltage on a reference node;
• providing a supply voltage on a supply node;
• differentially amplifying the reference voltage with a feedback signal to produce a differentially amplified signal;
• regulating a current through a first load device to generate the feedback signal;
• coupling the regulated current to the supply node through a second load device;
• and
• modulating current through the first and second load devices using the differentially amplified signal such that the voltage drop across the second load device is determined by the reference voltage.

An apparatus for generating a desired voltage that is a fixed amount below a supplied voltage comprising:

• a supply node having the supplied voltage thereon;
• a current path conducting current from the supply node;
• a current regulating switch within the current path;
• first and second load devices in the current path and operatively coupled to the current regulating switch so that the same current flows in each of the first and second load devices, wherein the first and second load devices have an on-voltage determined by the current flowing in the current path;
• and
• a feedback circuit coupled to sense the on-voltage of the first load device and to maintain the on-voltage across the first load device at a preselected level by controlling the current regulating switch.