| 摘要 |
<p>An improved printer apparatus (20) includes a print head having a series of point-like radiation sources (30), such as LED's, arranged in a row for exposing a recording medium (11). Enabling logic (43) is provided for determining which of the point-like radiation sources are to be selected for energization. A current driver responsive to the logic provides electrical current to the radiation sources selected. The current driver includes a current mirror having a master circuit (44a) for generating a reference current and a plurality of slave circuits (44b) for providing respective driver currents to the radiation sources selected for energization. The master circuit includes a series of parallel connected transistors (55) that may be instantaneously reprogrammed by digital control signals to said transistors. The characteristics of the transistors vary so that currents from them are scaled by say powers of two to provide an expanded current control capability. Environmental conditions and/or aging often require change in current to maintain desired recording performance. The need for such change may be automatically sensed and a new digital control word sent to the transistors to adjust current to the radiation sources.</p> |
