Reference-less electro-thermal loop with window monitor

A circuit comprising:

• a first current mirror disposed within a substrate and having a reference terminal and an output terminal, the first current mirror including transistors of a first polarity;
• a first transistor disposed within the substrate and having a first terminal, a second terminal, and a control terminal, the first terminal of the first transistor coupled to the output terminal of the first current mirror, and the control terminal of the first transistor coupled to the reference terminal of the first current mirror, the first transistor having a second polarity;
• a second transistor disposed within the substrate and having a first terminal and a control terminal, the control terminal of the second transistor coupled to the second terminal of the first transistor, the first terminal of the second transistor coupled to the reference terminal of the first current mirror;
• a differential amplifier disposed within the substrate and having a first input terminal, a second input terminal, and an output terminal, the first input terminal of the differential amplifier coupled to reference terminal of the first current mirror;
• a second current mirror disposed within the substrate and having an output terminal and a reference terminal, the reference terminal of the second current mirror coupled to the second input terminal of the differential amplifier, the second current mirror including transistors of a second polarity, wherein the second polarity is opposite the first polarity;
• a third current mirror disposed within the substrate and having a reference terminal and an output terminal, the reference terminal of the third current mirror coupled to the output terminal of the second current mirror, and the output terminal of the third current mirror coupled to the reference terminal of the second current mirror;
• and
• a third transistor having a control terminal coupled to the output terminal of the differential amplifier.

A circuit comprising:

• a CTAT current source disposed within a substrate and having an output terminal;
• a PTAT current source disposed within the substrate and having an output terminal coupled to the output terminal of the CTAT current source;
• a heating element disposed within the substrate and having a control terminal coupled to the output terminal of the CTAT current source;
• a comparator disposed within the substrate and having an input terminal coupled to the output terminal of the CTAT current source;
• a voltage divider disposed within the substrate and having an output terminal coupled to a second input terminal of the comparator;
• and
• an AND gate having a first input terminal coupled to an output terminal of the comparator, and having a second input terminal coupled to the output terminal of the CTAT current source.

A circuit comprising:

• a temperature-dependent circuit and controller disposed in a package and having an output at a predetermined temperature;
• a variable heater disposed in the package and having a control terminal;
• and
• a differential absolute-temperature comparator disposed in the package and having an output terminal coupled to the control terminal of the variable heater, wherein the differential absolute-temperature comparator is configured to:
• source a first current to the control terminal of the variable heater that increases with an increase in temperature;
• and
• sink a second current from the control terminal of the variable heater that decreases with an increase in temperature,
• wherein the first current equals the second current at the predetermined temperature.