sig_gen extension

Hi John,

I'm trying to perform some receive system fault finding, and I'd like to understand how the sig_gen extension works a bit better.

Where exactly does it inject the signal into the Kiwi ?

Is it an actual RF signal injected into the antenna port before the LPF, or is it a bit further down the chain ?

Does it actually make use of the ADC, or is it routed internally in the FGPA simulating an ADC output and therefore entirely bypassing the whole ADC stage ?

No need for a detailed reply, just a quick answer would be fine. I'm just trying to understand the basics.




  • It's all digital inside the FPGA. It's just a DDS that gets switched in place of the ADC input.

  • Hi John,

    OK thanks for that.

    Just to clarify, if the ADC was faulty, the internal signal generator would still give the correct levels ?



  • Yes. The ADC XO (separate part from ADC itself) has to be working. But otherwise bad outputs from the ADC itself shouldn't affect things when in sig gen mode.

  • As I understand it, sig-gen is an FPGA software tool. What if we try to use a free GPIO and generate a hardware PWM signal to test the ADC?

  • Yes. That's a very good idea and has not gone unnoticed..

  • edited July 15

    Thanks, John. We always ready to give you new ideas. And I really hope that you will be able to implement them.

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