Dual-range analog-to-digital convertor

Claim 1

An electronic computing scale comprising: load cell means for providing a raw analog voltage representative of weight bearing on said load cell means; analog-to-digital convertor ("ADC") means, having an ADC input terminal adapted to receive an analog input voltage, for providing a digital ADC output signal representative of the input voltage at said ADC input terminal, said ADC means operating to provide unique digital output signals for input voltages lying within a predetermined permissible range; first transform means, responsive to the raw voltage, for providing a first transformed voltage lying within a first voltage sub-range contained within said permissible range when the weight is in a low sub-range; second transform means, responsive to the raw voltage, for providing a second transformed voltage lying within a second voltage sub-range contained within said permissible range when the weight is in a high sub-range; said first and second transformed voltages being characterized by respective first and second variations as a function of weight, the first characteristic variation exceeding the second characteristic variation; a range flag having at least first and second states; switch means, responsive to the state of said range flag, for applying said first transformed voltage to said ADC input terminal when said range flag is in its first state and said second transformed voltage to said ADC input terminal when said range flag is in its second state; and logic means, responsive to said ADC output signal and to the state of said range flag, for controlling said range flag so that if said range flag is in its first state and said ADC output signal corresponds to an input voltage outside said first voltage sub-range, said range flag is set to its second state, and if said range flag is in its second state and said ADC output signal corresponds to an input voltage outside said second voltage sub-range, said range flag is set to its first state.