A N 5 4 3
16
Rev. 0.9
6.2. Alternate Frequency (AF) Timing
The Si4754/55/56/57 features a flexible FM tune command that allows for a number of operational choices. While
tuned to the current station, the receiver can quickly tune to candidate FM stations and perform one of three
operations.
1. Tune to the FM station and stay tuned.
2. Tune to the FM station; check the selected signal metrics, and jump back to the original station (AF check).
3. Tune to the FM station; check the selected signal metrics, and decide if the receiver is kept tuned to the FM
station (AF Jump) or re-tuned to the original station.
The timing diagrams for AF tune and AF check are shown in Figure 5 and Figure 6, respectively.
Figure 5. AF Tune Diagram
AF Tune
command
issued
AF Tune
Initiated
F
1
F
1
F
2
AF station metrics qualified:
Above thresholds
Tuner stays on AF station
Audio
Audio
F
2
}
F
2
T
2
T
3
T
1
T
1
T
1
~ 0.5 ms
T
2
~ 1 ms
T
3
~ 4.8 ms
