| 摘要 |
<p>A DC-coupled active pull-down ECL circuit ('LS-APD') has a pull-down drive that self adjusts to lead conditions. A current source (Q3) sinks emitter current from first (Q1) and second (Q2) bipolar transistors. The input signal (IN) is coupled to the base of the first transistor, whose collector signal is coupled to the base of a pull-up transistor (Qpu) whose emitter is the LS-APD output voltage node (OUT). The pull-up transistor is coupled between the upper rail (Vcc) and the second transistor's collector load resistor (R2). A pull-down transistor (Qpd) has its base coupled to the second transistor's collector, its collector coupled to the LS-APD output node, and its emitter coupled to a node receiving a regulated (Vreg) voltage. As load capacitance increases, the output voltage takes longer to drop sufficiently to turn off the pull-down transistor.</p> |
