I am trying to implement a FSK demodulator using a uC. I want to multiply the FSK modulated signal by its delayed version (delayed by 448 usec). How can I implement the delay block and multiplier block using discrete components (opamps, transistors etc)

 

It sounds to me like you are mixing analog and digital. I am no pro, but I think you need to work either in analog or in digital, not both.

 

This uses uC: http://www.ti.com/lit/an/slaa037/slaa037.pdf

 

Well FSK is sort of Digital to analog conversion, and there are various ways to demodulate it one of which requires to multiply a FSK signal by its delayed version and then filtering it to get the digital data so in short how to multiply an analog signal with its delayed version, sort of a delay multiplier
http://en.wikipedia.org/wiki/Carrier_wave

 

Well, forget the delay for a second, you will need an analog multiplier that works on the frequency used. What are the two frequencies that you want to demodulate?

 

Well, forget the delay for a second, you will need an analog multiplier that works on the frequency used. What are the two frequencies that you want to demodulate?

1200 Hz (binary 1) and 2200 Hz (binary 0)

 

And what is the bitrate, i.e. how many cycles does one bit last? You could simply use a comparator and measure the period between cycles and decide whether it is 1200 or 2200 hz.

 

And what is the bitrate, i.e. how many cycles does one bit last? You could simply use a comparator and measure the period between cycles and decide whether it is 1200 or 2200 hz.

bitrate is 1200 bits/ second, I did some reading, it is more noise tolerant this way

 

there were circuits using pll chips for this in the old signetics books. some of the 5xx series chips.

 

there were circuits using pll chips for this in the old signetics books. some of the 5xx series chips.

Yes, they had tone decoders - used for push-button telephones and such. The 567 and ???

At 1200 and 2200 Hz, you could connect your pulses to an input pin of the micro and look for zero-crossings - then use the timer to count cycles to see if you have delay between pulses for 1200 or 2200 (you could even count the pulses and determine how many make each bit).

 

We used to use an XR2211 for FSK