| 摘要 |
The gate drive voltage of the PMOS pull-up output transistor P1 is not dependent on the input-output voltage supply VDDIO. Hence the pull-up slew rate does not vary when the supply VDDIO is changed. An earth-referred current source Ip is enabled by a high data signal A to pass a constant current through a resistor R1 coupled to the supply VDDIO and so generate a gate-source drive voltage which is invariant of VDDIO. The pull-down transistor N1 is driven by a second switched constant current. The voltage supply VDD for the pull-down control circuit 204 is lower than VDDIO and is typically a fixed core supply voltage. The output driver may be used in a solid-state imager IC (figure 4), which may be part of a digital camera or other imaging system (figure 5). The stabilized output current drive and slew rate reduces switching noise without the need for thicker tracks. |
