D latch

Latches are designed to be transparent. That is, input signal changes cause immediate changes in output. Flip-flops, on the other hand, have their content change only either at the rising or falling edge of the clock signal. After the rising or falling edge of the clock, the flip-flop content remains constant even if the input changes

The D latch as shown below has an enable input. When the E input is 1, the Q output follows the D input. In this situation, the latch is said to be "open" and the path from the input D to the output Q is "transparent". Thus the circuit is also known as a transparent latch. When E is 0, the latch is disabled or "closed", and the Q output retains its last value independent of the D input.

The truth table and diagram


  • The green switch is a on/off switch (similar to a room light switch).
  • Q0 is the previous state of Q and Q0 is the previous state of Q.
  • Output Q depends on E (Enable)
    • E (Enable) high: Input passes to output
    • E (Enable) low: Latch holds its output
  • The D Latch is level sensitive and transparent.
  • Watch the video to learn how to edit the input (thick) waveforms.

Thank you for learning from electronics-course.com

We do not have a paywall as our mission is to provide everyone from Albania to Zimbabwe, rich or poor, a quality foundational electronics education. With advertising revenues falling despite increasing numbers of learners, we need your help to maintain and improve the course, which takes time, money and hard work.

If everyone who benefits from this course gives as little as $2 via Paypal, we can continue to achieve our mission. Thanks!

Support Our Mission