JPS57201328A - Binary-coded weighting constant current source circuit - Google Patents

Abstract

PURPOSE:To produce a binary-coded weighting constant current source which can form an integrated circuit by providing a titled circuit with plural variable constant current sources in accordance to the outputs of plural sample holding circuits in addition to a current adding circuit and a differential circuit. CONSTITUTION:In the 1st status, a current adding circuit 3 supplies only an output of a standard constant current source 2 to a differential circuit 17 as an output 24 by a control signal 23 of a controlling circuit 4. The differential circuit 17 transmits the difference between an output of a variable constant current source 6 and the output 24 to a sample holding circuit 5 on the basis of a control signal 22. By an output 18 of the controlling circuit 4, the circuit 5 is turned to sampling status, a current source 6 is changed and, when the current value of the current source 6 coincides with that of the constant current source 2, the circuit 5 is turned to holding status. In the 2nd status, the adding circuit 3 adds outputs of the current sources 2, 6 according to the control signal 23 and supplies to the added value the differential circuit 17. The differential circuit 17 transmits the difference between the output 24 of the adding circuit 3 and an output of a current source 9 to a sample holding circuit 8, so that the the circuit 8 is turned to sample status the output of the current source 9 is made coincide with the sum of outputs of the current sources 6, 2, twice the current value of the current source 6. In the same manner, outputs of current sources 12, 15 become 4 and 8 times the current value of the current source 6.