| 摘要 |
PURPOSE:To reduce the maximum instantaneous current in a reset period and approximating the middle point of the analog signal of output of an integrator to an earth level, by receiving a constant current source which is integrated just for a period corresponding to the digital data and a current source set in the current direction and setting said current source under a conduction mode just for a fixed period. CONSTITUTION:The digital data is set to a counter 3, and a current switch 4 is closed just for a conduction period 33 corresponding to the data. Therefore the current of a constant current source 5 flows to an integrator 12, and an output 10 is turned into an analog waveform 30. While the current of a constant current source 26 flows to the integrator 12 since a switch 27 is closed just for a fixed period by a control circuit 28. Then the output 10 is turned into an analog waveform 31. In fact an analog waveform 29 is obtained by adding both waveforms 30 and 31 together since both switches 4 and 27 conduct at a time. Both the current value of the source 26 and the conduction period of switches are decided by defining the analog waveform of output of the integrator 12 as the middle point of an earth level. In such a way the reduction of a dynamic range is prevented and needs no overcurrent that performs the instantaneous charging in a reset period. |
