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#1 2016-02-12 18:56:06

badelvis
Member
Registered: 2016-02-12
Posts: 2

Questions related to RF Frontend

Dear all,

I am writing because I am trying to understand the Proxmark3 schematic (or, more precisely, the RF frontend).

I have a strong engineering background. I got quite a bit of experience with PCB design, hardware and embedded software development and FPGAs. When it comes to analog RF design, I am still a beginner, though. From studying the Proxmark3 schematic and software available on Github, I believe to have found out the following details. I would be glad if you could correct me, if I'm wrong.

1. The LOxxx/HIxxx RX paths are used for 125 MHz/13.56 MHz systems.
2. The xxRAW/zzPKD RX paths are used to sample the raw RF signal/the output of an envelope detector.
3. The analog TX path is only used when the Proxmark3 operates as PCD (i.e. a reader) and not when it is used as PICC (i.e. as tag).

Could you provide feedback for the following points, that I still do not understand?

4. Why are there so many coil drivers?
5. Why are they driven by the FPGA whose output is a square wave with lots of high-frequency components?
6. Is XT1 the crystal responsible for generating the reference clock for the RF signal?
7. When operating as PICC, the Proxmark3 must modulate the antenna load to transfer data back to a PCD. Where in the schematic can I find the load modulation circuit?
8. What are the CROSS_LO and CROSS_HI inputs to the FPGA used for?

In general, what are the main reasons for including an FPGA and a dedicated ADC chip in the design? Using newer hardware, do you think it would be possible the achieve the similar functionality using an ARM-enabled SOC with some analog peripherals (ADC, OpAmps, Comparators)? Higher sampling frequency of the ADC? True parallel processing via the FPGA?

Thanks for open-sourcing this great piece of hardware.
Also, thanks in advance for your help!

Best, badelvis

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#2 2016-02-13 09:58:15

badelvis
Member
Registered: 2016-02-12
Posts: 2

Re: Questions related to RF Frontend

I read system.txt now. It carries a notice that it is outdated, however.

Regarding my questions, I can answer some of the myself.

4: To achieve different output levels (i.e. modulate the amplitude) by driving only some of them.
5: The fact that this produces high-freq. components is accepted.
6: ?
7: ?
8: They are used to recover the RF clock/phase.

Best, badelvis

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#3 2016-03-16 08:07:58

JohannWiles
Member
Registered: 2016-03-16
Posts: 1

Re: Questions related to RF Frontend

Hi everyone. I am new here and have lot of queries with me. I am also a PCB and Hardware design engineer and in the learning stage also.
Can you please tell me what is the Proxmark3 schematics? What are its its specifications and applications?
Can i use them for the design of the high frequency circuits?

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