Trimming resistor using modulated signal

An apparatus comprising:

• a circuit having a first terminal and a second terminal;
• a first resistor coupled to the first terminal, the first resistor having a first resistance;
• a second resistor coupled to the second terminal, the second resistor having a trim input;
• and
• a modulator circuit having a control input and a modulator output, the modulator output coupled to the trim input, the modulator circuit configured to set a duty cycle of a modulated signal at the modulator output based on matching an average second resistance of the second resistor to the first resistance.

A method comprising:

• setting a first terminal of a first resistor network and a second terminal of a second resistor network to a first voltage, the first resistor network having a third terminal and the second resistor network having a fourth terminal, the second resistor network including a first trimmable resistor having a first trim input and a second trimmable resistor having a second trim input coupled between the second terminal and the fourth terminal;
• providing a modulated signal having a first duty cycle at the first trim input based on a first trim code;
• with the modulated signal having the first duty cycle, sweeping a second trim code at the second trim input through a set of first values;
• selecting one of the first values for which a voltage difference between the third and fourth terminals is at a minimum;
• with the second trim code at the second trim input set to the one of the first values, varying a duty cycle of the modulated signal by sweeping the first trim code through a set of second values;
• selecting one of the second values for which the voltage difference is below a threshold;
• determining a calibrated first trim code based on the one of the first values;
• determining a calibrated second trim code based on the one of the second values;
• and
• storing the calibrated first trim code and the calibrated second trim code in a memory.