ADC bit width and sample rate

[briansune]

Hi,

After reviewing a bit the HW schematic, there are couple of questions come to my mind.

1. NFC usually only require bandwidth of 14kHz so if we filter and demodulate the incoming signal after the narrow band filter. The ADC Nyquist bandwidth should only require less than 100kHz?

2. As this example is using 3MSPS then this also raise a question that the incoming signal is filtered via CIC / IIR / FIR? As we just need a delta in ASK?

I am not sure these questions are incorrect or hard but I guess this could help other developers.

Bests,
Brian

ENJOY~

[WangXuan95]

1. The bit rate is 105.9375 kHz, not 14 kHz.
2. There is a digital median filter in the code (similar to the effect of a low pass filter)

[briansune]

• The bit rate is 105.9375 kHz, not 14 kHz.

Read carefully my friend. Did I written BIT-RATE or bandwidth?

[WangXuan95]

NFC usually only require bandwidth of 14kHz

Since the bitrate is 105khz, how can the signal bandwidth be only 14khz?

[briansune]

@WangXuan95

Bandwidth and bit rate is two store my friend. You can try to calculate or find explanation online.
Here is a short PDF explains NFC support bit-rates and bandwidth.

https://www.andrew.cmu.edu/course/14-760-s20/applications/ln/14760-l19.pdf

[WangXuan95]

After checking, it seems that the bandwidth of NFC is indeed 14kHz. So could you provide more detail of your idea - how to decode NFC ISO14443A signals with ADC less than 200ksps? If this idea is feasible, it may be a good way to reduce costs.

[briansune]

@WangXuan95

Interesting~

You had correct me on wrong bandwidth on RF then you request me to provide more detail, while you then changed the BW is correct.

BTW I appreciate you had answered my 2nd question close this issue and thank you for your time.