Analog-digital converting circuit having high resolution and low power consumption

An analog-digital converting circuit comprises an analog amplifying circuit having an input connected to an analog signal input terminal and having a plurality of outputs for generating a corresponding number of analog signals amplified by different amplification factors. A first selector is connected at its a corresponding number of inputs to receive the plurality of amplified analog signals, respectively. The first selection circuit outputs one analog signal selected from the received amplified analog signals, to an analog-digital converter. A second selector is connected at its an input to receive a digital signal from the analog-digital converter and has a plurality of outputs for outputting the received digital signal from one sequentially alternatively selected from the plurality of outputs. A coefficient multiplying circuit has a corresponding number of inputs connected to the plurality of outputs of the second selector, respectively, and a plurality of outputs for generating a corresponding number of multiplied digital signals which are obtained by the plurality of outputs of the second selector by different coefficients, respectively. A third selector is connected at its corresponding number of inputs to the plurality of outputs of the coefficient multiplying circuit so as to output, as a digital signal, one selected from the plurality of outputs of the coefficient multiplying circuit. A controller is connected to receive the plurality of outputs of the second selector for monitoring respective levels of the plurality of outputs of the second selector and for supplying a selection signal to the third selector so as to cause to select, from the plurality of outputs of the coefficient multiplying circuit, one multiplied digital signal in correspondence to a level of the analog signal.inputted to the analog signal input terminal.