Method and apparatus for field-effect transistor current sensing using the voltage drop across drain to source resistance that eliminates dependencies on temperature of the field-effect transistor and/or statistical distribution of the initial value of drain to source resistance

A circuit for generating a signal which is proportional to current flowing into or out of a drain of a first FET, the circuit comprising:

• a second FET comprising a gate, a source, and a drain, wherein the gate of the second FET is configured to receive a voltage, and wherein the source node of the second FET is configured to be coupled to ground;
• an operational amplifier comprising an inverting input node, a non-inverting input node, and an output node, wherein the inverting node is coupled to the drain of the second FET, and wherein the non-inverting node is coupled to the drain of the first FET;
• a resistor coupled between the inverting node and an output node;
• and
• a second circuit coupled to the output node of the operational amplifier, wherein the second circuit is configured to compare a predetermined signal with a signal generated by the operational amplifier at the output node thereof, wherein the second circuit is configured to generate a second signal indicating that a predetermined current limit when the signal generated by the operational amplifier is greater in magnitude that the predetermined signal, wherein the predetermined signal represents a value calculated as a function of the predetermined current limit and a ratio of areas of the first and second FETs.

A method comprising:

• activating a first FET, wherein the first FET comprises a source and a drain, and wherein the first FET is implemented in a first semiconductor device;
• activating a second FET, wherein the second FET comprises a source and a drain, wherein the source of the second FET is coupled to ground, and wherein the second FET is implemented in a second semiconductor device which is separate from the first semiconductor device;
• activating an operational amplifier comprising an inverting node, an non-inverting node, and an output node, wherein the drain of the first FET is coupled to the non-inverting node, and wherein the drain of the second FET is coupled to the inverting node;
• the operational amplifier generating a signal at the output node thereof, wherein the signal is proportional to a current flowing into or out of the drain of the first FET.

A method comprising:

• activating a first FET, wherein the first FET comprises a source and a drain;
• activating a second FET, wherein the second FET comprises a source and a drain, wherein the source of the second FET is coupled to ground;
• activating an operational amplifier comprising an inverting node, a non-inverting node, and an output node, wherein the drain of the first FET is coupled to the non-inverting node, and wherein the drain of the second FET is coupled to the inverting node;
• and
• the operational amplifier generating a signal at the output node thereof, wherein the signal is proportional to a current flowing into or out of the drain of the first FET;
• wherein the signal represents the current flowing into or out of the drain of the first FET multiplied by a resistance of a resistor coupled between the output node and the inverting node and the ratio of areas of the first and second FETs, respectively.

A method comprising:

• activating a first FET, wherein the first FET comprises a source and a drain, wherein the drain of the first FET is coupled to a power supply, and wherein the first FET is implemented in a first semiconductor device;
• activating a second FET, wherein the second FET comprises a source and a drain, wherein the source of the second FET is coupled to ground, and wherein the second FET is implemented in a second semiconductor device which is separate from the first semiconductor device;
• activating an operational amplifier comprising an inverting node, a non-inverting node, and an output node, wherein the drain of the first FET is coupled to the inverting node, and wherein the drain of the second FET is coupled to the inverting node;
• the operational amplifier generating a signal proportional to a current flowing into or out of the drain of the first FET, wherein the signal is generated as a function of a voltage at the drain of the first FET measured with respect to ground.

A method comprising:

• activating a first FET, wherein the first FET comprises a source and a drain, and wherein the drain of the first FET is coupled to a power supply;
• activating a second FET, wherein the second FET comprises a source and a drain, and wherein the source of the second FET is coupled to ground;
• activating an operational amplifier comprising an inverting node, a non-inverting node, and an output node, wherein the drain of the first FET is coupled to the inverting node, and wherein the drain of the second FET is coupled to the inverting node;
• and
• the operational amplifier generating a signal proportional to a current flowing into or out of the drain of the first FET, wherein the signal is generated as a function of a voltage at the drain of the first FET measured with respect to ground, wherein the signal represents the current flowing into or out of the drain of the first FET multiplied by a resistance of a resistor coupled between the output node, and the inverting node and a ratio of areas of the first and second FETs, respectively.