Methods and apparatus for calibrating temperature measurements and measuring currents

An apparatus comprising:

• biasing circuit means having an input, a reference voltage output and a biasing voltage output;
• output current source means coupled to the biasing voltage output and configured to produce an output current;
• and
• offset circuit means coupled in a feedback loop between the reference voltage output and the biasing circuit input and configured to generate from the reference voltage output a variable offset voltage for selectively controlling the biasing voltage applied to the output current source means.

An apparatus, comprising:

• a processing chamber;
• a reflector disposed inside the processing chamber;
• a light pipe extending through the reflector;
• and
• a circuit board coupled directly to the light pipe, where the circuit board has a photodetector and a calibration current source that includes
• a biasing circuit having an input, a reference voltage output and a biasing voltage output,
• an output transistor current source coupled to the biasing voltage output and configured to produce an output current, and
• an offset circuit coupled in a feedback loop between the reference voltage output and the biasing circuit input and configured to generate from the reference voltage output a variable offset voltage for selectively controlling the biasing voltage applied to the output transistor current source.

An apparatus comprising:

• an amplifier having an input and an output;
• a capacitor coupled between the input and the output of the amplifier;
• a transistor coupled in parallel with the capacitor between the input and the output of the amplifier;
• and
• a switch coupled in parallel with the capacitor and the transistor between the input and output of the amplifier.

A method, comprising:

• generating a calibration table by applying a plurality of input signals to a calibration current source to produce a plurality of output signals;
• storing the calibration table;
• receiving an output signal of a photodetector;
• and
• determining the calibration input signal corresponding to the received photodetector output signal based upon the stored calibration table.