Apparatus and method for measuring load current by applying compensated gain to voltage derived from drain-to-source voltage of power gating device

An apparatus, comprising:

• a power gating field effect transistor (FET) comprising a gate, a source, and a drain, wherein the source is coupled to a voltage rail, wherein the drain is coupled to a load, and wherein the gate is configured to receive a gating voltage to selectively turn on the power gating FET to allow a load current to flow between the voltage rail and the load by way of the power gating FET;
• and
• a differential amplifier configured to generate a current-related voltage related to the load current by applying a gain to an input voltage, wherein the input voltage is based on a drain-to-source voltage of the power gating FET, and wherein the gain varies inversely with the input voltage in response to variation in temperature or gate-to-source voltage of the power gating FET, wherein the differential amplifier comprises:
• an operational amplifier;
• a first compensating PMOS device including a first gate, a first source, and a first drain, wherein the first compensating PMOS device is coupled between the source of the power gating FET and a first input of the operational amplifier, wherein the first gate is configured to receive a first gate voltage substantially the same as the gating voltage that turns on the power gating FET;
• a second compensating PMOS device including a second gate, a second source, and a second drain, wherein the second compensating PMOS device is coupled between the drain of the power gating FET and a second input of the operational amplifier, wherein the second gate is configured to receive a second gate voltage substantially the same as the gating voltage that turns on the power gating FET;
• and
• at least one feedback resistor coupled across an output of the operational amplifier and one of the first or second inputs of the operational amplifier, wherein the current-related voltage is generated at the output of the operational amplifier.