Leader-follower flip-flop

Leader-follower D flip-flops¹ are flip-flops that consist of two gated D-latches where the first is a leader, and the second is a follower. Observe the patterns in the timing diagram.² The leader changes at the clock’s positive edge, while the follower changes state at the clock’s negative edge. This is so that the leader will track the $D$ input signal and the follower won’t change when the clock is at 1. $Q_m$ follows any changes in $D$, and $Q_s$ will remain constant.

Then, when the clock changes to 0, the leader stops following changes. Since $Q_m$ doesn’t change during this period, the follower output can only change at most one time.

The output of the circuit follows the negative edge of the clock.

Footnotes

1. Historically called “master-slave flip-flops”. Not anymore for obvious reasons. ↩

2. From Prof Korst’s lecture notes. ↩