Gain Amplifier & demodulator

[surjo_dm]

Hi guys,
can anybody explain me what is a Gain Amplifier and a demodulator in an IR receiving unit of TVs and VCRs? Does the Gain Amplifier refer to the usual voltage or current amplifier.
Thanks,
Surya

 

[Nigel Goodwin]

Hi guys,
can anybody explain me what is a Gain Amplifier and a demodulator in an IR receiving unit of TVs and VCRs? Does the Gain Amplifier refer to the usual voltage or current amplifier.
Thanks,
Surya

The amplifier does both voltage and current (as most do). An IR receiver in a TV has to do a number of different jobs:

1) Pickup the IR signal.

2) Amplify it.

3) Apply AGC to take account of very wide variations in signal strength.

4) Demodulate the signal.

5) Compare the frequency of the signal to the specified modulation frequency.

6) Switch the output high or low, depending on the result of 5).

The small 3 pin devices work extemely well, it takes IR modulated at about 38KHz and gives a logic output. Be aware that all the internal processing takes time - pulse widths out of the receiver IC are narrower that those transmitted, this makes it difficult using simple RS232 type communciations with them. Usually specific IR protcols are used, the Sony SIRC's system is particularly nice and easy to do.