Method and apparatus for accurately measuring currents using on chip sense resistors
View Patent ↗Systems and methods for managing process and temperature variations for on-chip sense resistors are disclosed. The system includes a circuit that can leverage a linear gm circuit in order to provide linear gains (positive gains and/or negative gains). The linearity of the circuit enables compensation for temperature and process variations across an entire range of current (positive to negative). A control signal is generated by using a linear gm amplifier and a replica resistor, which is substantially similar to the on chip resistor. The control signal is used to control the gain of a disparate linear gm amplifier within a compensation circuit, which provides an offset voltage to compensate for the variation in resistance of the on chip resistor.
1. A method for measuring a load current with an on-chip resistor, the method comprising:
generating an output voltage proportional to the load current flowing through the on-chip resistor;
generating a control signal indicative of a resistance value of a replica resistor by causing a desired full-scale current to flow through the replica resistor, and comparing a voltage across the replica resistor with a desired full-scale voltage; and
utilizing the control signal, adjusting the output voltage to account for a change in a resistance value of the on-chip resistor; wherein,
a temperature coefficient of the replica resistor is substantially similar to a temperature coefficient of the on-chip resistor, the resistance value of the replica resistor varies in proportion with the resistance value of the on chip resistor, and the adjusted output voltage indicates a measure of the load current through the on-chip resistor.
2. The method of claim 1 , wherein the adjusting the output voltage comprises controlling a gain of a linear transconductance amplifier utilizing the control signal.
3. The method of claim 2 , further comprising:
providing the output voltage as an input to the linear transconductance amplifier; and
adding a voltage proportional to an output current of the linear transconductance amplifier to the output voltage.
4. The method of claim 2 , further comprising: causing the current generated by the linear transconductance amplifier to flow through a compensation resistor for generating an offset voltage.
5. The method of claim 4 , correcting an error including adding the offset voltage to the output voltage.
6. The method of claim 4 , wherein the current generated by the linear transconductance amplifier changes linearly as a function of the output voltage.
7. The method of claim 1 , wherein the output voltage is indicative of the resistance value of the on-chip resistance.