[USRP-users] Sample rates and bandwidths on B210?

Ian Buckley ianb at ionconcepts.com
Thu Apr 16 15:20:11 EDT 2015


Tyler,
(If you care about the internals of the radio then ADI's document UG-570 "AD9361 Reference Manual" is recommended reading though it still leaves a lot to be guessed.)

In short:
The 61.44MHz maximum value is a limit on the sample rate of data fed to the Radio IC (31.72MHz in 2x2 MIMO mode). Ettus research call this the master_clock_rate, in contrast to the sample_rate, which is the sample clock between host computer and USRP. The actual radio IC contains a lot of configurable digital filters and the converters use a sigma-delta design style that typically runs at 100's of MHz. In addition the FPGA offers more configurable digital filtering. The decimation/interpolation range in the FPGA ranges from 1 through 512, however certain values should be avoided (Generally all odd values except 1) . The Radio IC has decimation/interpolation between 1 and 48 ( typical values is around 8->16 for sample rates commonly used). Every decimation/interpolation stage includes filtration thats as close to the Nyquist limit as practically possible. In addition there are 2 stages of analog baseband filter which are programmable with fine granularity, and these are what is being referred to via the "*_bandwidth" API calls. Until recently get_rx_bandwidth always returned a hardcoded 56e6, but now returns the actual programmed bandwidth..you are advised to work with recent versions of UHD with the B2x0.

-Ian


On Apr 16, 2015, at 10:23 AM, "Weaver, Tyler via USRP-users" <usrp-users at lists.ettus.com> wrote:

> Signed PGP part
> When I run get_rx_rates on my b210 I get values that seem to be integer decimations of 64 MS/s vs the 61.44 MS/s value that I see in the documentation.  It also seems that the minimum decimation is 2 as the maximum value is 32e6 (64/2).  Is the correct?  Is there an up sampling stage in the B210 similar to to the N210 after the ADC?
> 
> Also when I run get_x_bandwidth_range there are only two values 200e3 and 56e6 that are output.  Are these my only two options for filters before the 64/61.44 MS/s ADC?
> 
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