Current measuring methods

A method for measuring a current passing through a load, comprising:

• directing a first current through a power transistor having a first terminal connected to substantially constant voltage and a second terminal connected to the load;
• connecting a variable capacitor in parallel with the power transistor with a plurality of sampling switches;
• and
• causing the variable capacitor to have a capacitance inversely proportional to a resistance of the power transistor, whereby a charge stored on the variable capacitor is proportional to the current passing through the power transistor when the sampling switches are opened.

A method of measuring a current passing through a load, comprising:

• completing a circuit between the load and a substantially constant voltage with a transistor that has a first terminal and a second terminal, the power transistor including N substantially identical transistor elements;
• connecting a first terminal of a first reference transistor to the first terminal of the power transistor, the first reference transistor including M substantially identical transistor elements, the transistor elements of the first reference transistor fabricated with substantially the same process and dimensions as the transistor elements of the power transistor;
• comparing a voltage at a second terminal of the power transistor to a voltage at the second terminal of the first reference transistor with a first comparator;
• generating a first known current with a first current source that is connected to the second terminal of the first reference transistor, whereby a digital signal is output on a first reference line connected to an output of the first comparator indicative of whether the current passing through the load is greater than N/M times the first known reference current;
• connecting a first terminal of a second reference transistor to the first terminal of the power transistor, the second reference transistor including L substantially identical transistor elements, the transistor elements of the second reference transistor fabricated with substantially the same process and dimensions as the transistor elements of the power transistor;
• comparing a voltage at the second terminal of the power transistor to a voltage at the second terminal of the second reference transistor with a second comparator;
• and
• generating a second known current with a second current source that is connected to a node between the second terminal of the second reference transistor and the second input of the second comparator, whereby a second digital signal is output on a second reference line connected to the output of the second comparator if the current passing through the load is greater than N/L times the second known reference current.