Analog-digital converting circuit having high resolution and low power

Abstract

An analog-digital converting circuit comprises an analog amplifying circuit having different amplification factors and an input connected to an analog signal input terminal. A first selector is connected at 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 is connected to the outputs of the second selector, and generates multiplied digital signals obtained by multiplying the outputs of the second selector by different coefficeints. 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. y