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ASK Demodulator

Discussion in 'General Electronics Discussion' started by shaikss, Jun 26, 2013.

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  1. shaikss


    Aug 17, 2011

    I am designing an ASK demodulator for RFID Tags. I have attached the circuit diagram. This is the ckt from IEEE paper.
    If you look at the ckt, the first stage is the inverter kind of thing. I didn't get why second NMOS is used for Stage I. Similarly, the second stage is also inverter with two NMOS. Again, the question is why second NMOS. But when I checked the output of that stage, it is acting like a latch. The last stage is buffer.

    I generated ASK modulated signal and fed as input to the demodulator. I expected that whenever modulated signal is present, demod output is '1' and when no signal is present, it is '0'. To my great surprise, it is always '1'. I tried to give the input by delaying it. So, for the very first time, because of the delay, I could see a logic '0`' at the output. After the delay, there is signal and so the output is logic '1'. Afterwards, though there is no signal, I don't see logic 0 at the output. Its always high. I assumed that the second NMOS at second stage is acting like a latch. Please let me know how can I redesign it? Or Is my understanding wrong? I have attached the simulated results.

    Attached Files:

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