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This circuit uses an LM329, LM334, and an LT1056 to form a temperature to frequency converter. The LM334 temperature sensor pulls a temperature dependent current (0.33%/°C) from the LT1056's positive input node. This point, biased from the LM329-driven resistor string, responds with a varying, temperature-dependent voltage. The voltage varies the operating point of the LT1056, configured as a self-resetting integrator. The LT1056 integrates the LM329 referenced current into its summing point, producing a negative going ramp at its output. When the ramp amplitude becomes large enough, the transistors turn on, resetting the feedback capacitor and forcing the LT1056's output to zero. When the capacitor's reset current goes to zero, the transistors go off and the LT1056 begins to integrate negatively again. The frequency of this oscillation action is dependent on the LT1056's DC operating point, which varies with the LM334's temperature. The circuit's DC biasing values are arranged so that 0°C to 100°C sensor temperature excursion produces 0kHz to 1kHz at the output. This circuit has a stable 0.1°C resolution with a +/- 1.0°C accuracy.
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