| 摘要 |
<p>A transmitter circuit (10) for transmitting a digital data signal over a bus line (14) in a digital data processing system includes a MOSFET bus driver transistor (11) having a gate to drain capacitance (CGD) which substantially dominates other capacitances at the gate terminal. The bus driver transistor (11) is driven by a buffer circuit (12) having pull-up and pull-down transistors (16, 17), the current through which is controlled by current sources (20, 21). The gate terminal of the driver transistor (11) is connected to, and controlled by, the node (22) between the pull-up and pull-down transistors (16, 17). The drain terminal of the driver transistor (11) is connected to, and controls, a bus line (14). To assert a signal on the bus line (14), the pull-up transistor is turned on to drive current into the node (22) at a rate governed by the current source (20), which increases the voltage level of the node (22). When the voltage level of the node (22) reaches the driver transistor's threshold level, the driver transistor (11) begins to turn on, allowing the voltage level of the bus line (14) to drop. Contemporaneously, current flows into the node (22) from the bus line (14) through the driver transistor's high gate to drain capacitance (CGD), thereby limiting the voltage level of the node (22), and thus the current flow through the driver transistor (11). Thus, current flows through the driver transistor (11) from the bus line (14) in a manner controlled, in part, by the voltage level on the bus line (14). In negating a signal on the bus line (14), the operations are similar, with current flowing out of the node (22) through the pull-down transistor (17) and the driver transistor's gate to drain capacitance (CGD).</p> |
