Synchronous demodulation of a RFID signal with a carrier of 134.200kHz

Question

Trivial problem but very difficult solution. I have to define a demodulator for an AM modulated signal. When a passive tag is excited with a sine wave of 134.200kHz (carrier of 3Vp-p) it send back a modulated signal and the level of signal is decreasing with 1/r^3 law, where r is the distance between the antenna and the tag. The depth of modulation is from 1% to 0,01% of amplitude of the carrier and the frequency of the signal of modulation is 4kHz.The difficult is to reach the distance of 40cm or more between the antenna and tag because the amplitude of demodulated signal is comparable with the noise. Now I'm analyzing the features of AD633 and I don't see an example of application to perform AM synchronous demodulation. I ask if someone has already used a AD633 to demodulate an AM signal. No answer to this question in the existing documentation. Thanks in advance of your attention. 
 Mauro

Mausine · Accepted Answer

Hi Sham 
 The way I used the AD633 was correct as explained in the datasheet where is described the synchronous demodulation. But a the end I did a hole in the water. The intrinsic noise of the component is from 8 to 10 mV without any signal to the inputs. So if the signal from the tag decreases under this value is impossible to decode it. It was a bad surprise because I didn't find any information on datasheet about this noisy characteristic of the component. 
 Now i'm evaluating the AD630 as possible alternative. But I don't know which is the mode the component use to perform the synchronous demodulation. So i'm in trouble because I have to decide quickly but i don't have elements to do a complete valuation. If someone is so polite to explain me the priciple of synchronous demodulation by sampling the input signals I will appreciate a lot. 
 Thanks in advance for attention.

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Synchronous demodulation of a RFID signal with a carrier of 134.200kHz

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