Alternative RF front-end chip and clock of the baseband

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Alternative RF front-end chip and clock of the baseband

Postby creese » Tue Jul 22, 2008 9:05 am

I have two question:
1st: What should I do if I wannt to change the zarlink gp2015 RF front-end chip into another one, for example the NJ1006AH/AK(Nemerix), STA5620(ST), SE4110L(SiGe). the same point of these chips is that they all have mag, sign and clock for the baseband part. but the IF frequence of them is 4.188/4.092MHz and clock is 16.368MHz, which is different from gp2015, 1.405MHz and 40MHz. I have read the verilog code of tracking module, there are some questions:
1)should I still use 40MHz, which will not be supply by RF front-end, for the tracking module using other RF front-end chip, even though the IF is 4.188/4.092MHz.
2)the frequence of "sample_enable" in accumulator.v is 5.714MHz, which is the same as the sample clock output to the gp2015 for a/d sample. but in other RF front-end chip, the a/d sample clock is 16.368MHz, so should I still use 5.714MHz sample_enable in accumulator.v if I change the gp2015?

2nd: the value of mag and sign is not mentioned in gp2015 datasheet and STA5620(ST), SE4110L(SiGe), I have read the verilog code and found sign 0 is -ve and 1 is +ve, I also read gp2021 datasheet and found it just show the truth table of mag and sign without +ve or -ve, so how do you know the sign of this input signal?
I guess it is unchangeable algorithmic of a/d transform and the value of the sign and mag is fixed. but when I saw NJ1006AH/AK(Nemerix), it sign is opposite to our code, that means its sign 0 is +ve and 1 is -ve, so I am lost...:CCC

thanks very much
creese
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Re: Alternative RF front-end chip and clock of the baseband

Postby agri » Tue Jul 22, 2008 3:22 pm

1) You are changing the time for the accumulation counter and the tic counter if you change the frontend clock. I would not recommend this, the change has to be accounted for in software. There is no need to do this until your frontend A/D converter samples with less than 40MHz.

2) The GP2015 is delivering new data with 5.7MHz, to avoid sampling the same data twice it is restricted here to only take every seventh sample. If you want to use a frontend with a higher sampling rate, it would be wise to change the sample_enable to accumulate all samples of this specific frontend. The values in the accumulator are much larger then, you have to make sure your software knows about that.

2nd You could just use !sign as input into the baseband module of course to avoid getting lost.
agri
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Re: Alternative RF front-end chip and clock of the baseband

Postby creese » Thu Jul 24, 2008 7:06 am

Thanks agri.
en...In fact I wannt to not only change the front-end chip, but also the nios cpu into New one - a opensource risc. It will be run over 100MHz. I dont know how many work need to be done...by the way it's a pretty time communicate with you. best wishes.
creese
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