| 摘要 |
PURPOSE:To decrease the number of a circuit element to simplify the constitution of a control circuit and to realize the big reduction of cost by using a D/A converting circuit using an inverting circuit in time division to obtain a time division differential current. CONSTITUTION:The output code of a counter 8b is supplied to multiplexers 4a and 4b to select two pieces of conductors which flow a current. Then, the output code of a counter 8a is changed and also inverted synchronously with the time division timing to be supplied to a D/A converting circuit 6. Thus a differential current is obtained and supplied to said two conductors. Then the output code of the counter 8b is converted to select the two pieces of conductors. Hereafter the same operation is repeated. As a result, the changing differential current is supplied successively and in time division to the conductors on an input screen 3. Thus the relative error of the differential current is reduced and the coordinate accuracy is improved.
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