1. Field of Invention
The present invention relates to a sensing circuit and, in particular, to a humidity sensing circuit with temperature compensation.
2. Related Art
FIG. 1 is a schematic diagram of a conventional temperature-humidity sensing circuit 1, which includes a humidity sensing unit 11, a temperature sensing unit 12, two analog-to-digital converters (A/D converters) 13 and 14, and a detecting unit 15. The humidity sensing unit 11 has an operation amplifier 111, a plurality of resisters R, and a plurality of sensors O. In the humidity sensing unit 11, the humidity signal detected by the sensor O is processed by the resistors R and operation amplifier 111 so as to output an analog signal S1 with respective to the humidity. Then, the analog-to-digital converter 13 converts the analog signal S1 to a digital signal S2. Meanwhile, the temperature sensing unit 12 measures the temperature to correspondingly output an analog signal S3, and then the analog-to-digital converter 14 converts the analog signal S3 to a digital signal S4. The detecting unit 15, which includes a comparison table and a microprocessor, receives the digital signals S2 and S4 with respective to the humidity and temperature respectively. The microprocessor outputs a suitable control signal S5 based on the comparison table in view of the digital signals S2 and S4.
The conventional temperature-humidity sensing circuit must detect the current temperature and humidity respectively, and then output the control signal through the detecting unit, so that two analog-to-digital converters are necessary. However, the analog-to-digital converter is a large and complicated circuit for converting the detected analog signal to a digital signal, and the digital signals with respective to the temperature and humidity must be integrated by the microprocessor. Accordingly, the entire temperature-humidity sensing circuit has a very complex circuit and involves large amount of electronic components, so that the manufacturing cost as well as the total volume is increased. Therefore, it is an important aspect of the present invention to provide a humidity sensing circuit with temperature compensation that has simple circuit design for detecting both temperature and humidity, thereby being suitable for further circuit design and application.