Hey all, I'm looking at some schematic for an FM IC. There is a pin that is labled MPX and it is said to be the multiplex output. Is this the mono signal? I'm just curious.
- posted
18 years ago
MPX or MPXO?
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- posted
18 years ago
Read the datasheet!
If you expect use to give you a useful answer, at least give us the part number of the IC, so we can look at the datasheet.
-- Peter Bennett, VE7CEI peterbb4 (at) interchange.ubc.ca new newsgroup users info : http://vancouver-webpages.com/nnq GPS and NMEA info: http://vancouver-webpages.com/peter Vancouver Power Squadron: http://vancouver.powersquadron.ca
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- posted
18 years ago
"MRW" wrote in news: snipped-for-privacy@o13g2000cwo.googlegroups.com:
The chip may have a built-in de-emphasis filter block (75uS?) which also produces some gain to more easily drive a power output stage. This "MPX" output comes in front of that (and therefore lacks the gain) but also has the full bandwidth to carry the added stereo sub-carrier centered at 38KHz.
So, if you want to build a simple, cheap monaural table radio, you ignore the "MPX" output (or maybe attach the 75uS de-emphasis network there) and connect the gain block output to a "power" amplifier chip through a volume controll and you're done.
If you want to go full stereo, you ignore the output gain block, connect the "MPX" output pin to a stereo decoder chip (usually available from the same manufacturer), connect dual de-emphasis networks to the outputs of the stereo demodulator chip then to dual volume controls and dual "power" amplifier chips.
"Power" amplifier chips might be in the neighborhood of 2 Watts with 10% distortion for a small table stereo rig!
HTH
Rick
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- posted
18 years ago
I suspect that that pin is used to indicate stereo signal carrier detected and locked. That is what it meant back in the '70's when i was using FM stereo decoder chips.
-- JosephKK
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- posted
18 years ago
Sorry Peter! The chip is actually a Philips TEA5767. On the datasheet, it just mentions that MPX is just the multiplex output pin. The chip also has outputs for the left and right audio channels, but I only want to use the mono output for now. I guess I can just connect my speaker drive to either one of the left and right channels.
Thanks!