Digital Logic Fundamentals Unit 7 – Tri-State Output
Exercise 2 – Source and Sink Current
EXERCISE OBJECTIVE
When you have completed this exercise, you will be able to demonstrate how a tri-state buffer
output can source and sink current by using the TRI-STATE OUTPUT circuit block. You will
verify your results with an oscilloscope and by observing the output LEDs.
EXERCISE DISCUSSION
- The discussion uses conventional current flow.
- Transistor-transistor logic (TTL) circuits function as current devices.
- When enabled (not high-Z) the TTL tri-state buffer can source or sink current.
- Current from a device is a source current: the device supplies current to an output load.
- Current from an output load is a sink current: the device provides a current path from the
load to ground.