Patent ID: 7382150

Claim:
A sensitivity switchable detection circuit, comprising: a first detection circuit having a first gain with respect to an input quantity, the first detection circuit outputting a first signal proportional to the input quantity; a second detection circuit having a second gain with respect to the input quantity, the second detection circuit outputting a second signal proportional to the input quantity; and an output switching circuit that outputs a detected signal associated with the input quantity by switching between the first signal and the second signal based on amplitudes thereof, thereby narrowing dynamic range of the detected signal, wherein the first gain defined as a ratio of the amplitude of the first signal to the input quantity is set higher than the second gain defined as a ratio of the amplitude of the second signal to the input quantity, the output switching circuit has a high gain region where only the first signal is selected for outputting the detected signal, a low gain region where only the second signal is selected for outputting the detected signal, and a middle gain region where a weighting function having a weighting factor outputs the detected signal by using both the first signal and the second signal as input variables so that the detected signal varies as a function of both the first signal and the second signal, and the output switching circuit uses the high gain region when the first signal or the second signal is smaller than a predetermined lower limit, the low gain region when the first signal or the second signal is larger than a predetermined upper limit, and the middle gain region when the first signal or the second signal is larger than the predetermined lower limit and smaller than the predetermined upper limit.