JPS6484922A - Sequential comparison type a/d converter - Google Patents

Abstract

PURPOSE:To quickly detect an overflow without necessitating the trouble of adding an additional circuit for detecting the overflow by providing an inexpensive weighting resistor having prescribed accuracy and a switching circuit for detecting the overflow. CONSTITUTION:In a final stage after a sequential comparison A-D converting operation is executed N-times, a reference signal generator 3 sets only a switching circuit S0 to a conducting state and applies a reference signal V to a weighting resistor R0, by which the resistor R0 outputs a reference signal V/2<n>, and also, switching circuits T connected to digital signals D1-DN of '1' become a conducting state, respectively, and since an output exists in weighting registers R1-RN connected to them, respectively, an adder 4 outputs a reference signal value adding their maximum (N+1) pieces, and a comparator 1 compares it with an analog input signal A and when the signal A is larger, a positive signal is generated. When the signals D1-DN of a digital signal register 2 are all '1', and the comparator 1 has generated the positive signal, A>=V is formed, therefore, an overflow detecting circuit 5 detects it as an overflow and generates an overflow signal O.