Satellaview AV Selector
The satellaview AV selector was conceived in order to prepare the decoded satellite signal for the satellaview, prevent the super famicom from monopolizing the TV's AV input, and allow for the use of a second BS decoder along with the one provided by ST. Giga. As is evident in the following diagram, the selector's internal circuit can be divided in three discrete units, each responsible of executing different functions:
*Bitstream division
This part allows the satellite signal to be used by tuners other than the Satellaview, in case somebody wishes to use other satellite-receiving equipment with the same television and tuner. This is done by an NJM2904 dual operational amplifier in a -so far- unknown configuration.
*Video signal search
An NJM2268 dual video amplifier handles this part. The patent which describes the AV selector includes a schematic of this very section, according to which the amplifiers are used in a comparator configuration:
(Note that since this schematic is sourced from the patent, the actual circuit might differ)
The purpose of this section is the generation of a control signal intended for the AV switching section.
*AV switching
This is handled by an NJM2284 2-input 3-channel video switch. According to the patent, it is capable of switching between the video signal generated by the Satellaview/Super Famicom, and the video signal provided by the BS tuner, depending on the value of the control signal generated by the video signal search section. This allows for using only one AV input both for playing satellaview/super famicom games and for watching conventional satellite broadcasts.
Further reading
Satellaview patent which describes the AV selector