Theory of Operation
2715 Spectrum Analyzer Service Manual 3-85
5. Steps 2 and 4 are repeated, retriggering eith ert he POS or ROS, until the
switch has stabilized in the closedposition.
6. Each single shot then times out approximately50 ms after the last valid
trigger.
7. Now the switch is released anda negative edge is presented to both the POS
and the ROS.
8. This edge triggers the ROS and its output becomesactive.
9. With the ROS output active andP OS output inactive,the POS is held in the
reset state by a NAND gate.
10. The ROS is retriggered, by each falling edge of the bouncing switch, until
the switch has stabilized in the openstate.
11. After approximately 50 ms, the ROS times out and its output becomes
inactive.
12. The POS and the ROS are ready for another key press.
Figure 3--27 shows the three possible scenarios of key presses and how the
debounce circuit reacts to each one.
(a) (b) (c)
POS
ROS
KEYINKEYIN
POS
ROS
NOTE: The dottedlines denote retrigger points relative to the KEY IN pulse transitions.
KEYIN
POS
ROS
Figure 3- 27: How the Debounce Circuit Reacts to Key Closure