Re: LMS6002D support of LTE

Hi John, On Sat, Oct 13, 2012 at 11:11 PM, John Orlando <john(a)epiqsolutions.com> wrote: > On Sat, Oct 13, 2012 at 3:47 PM, Alexander Chemeris > <alexander.chemeris(a)gmail.com> wrote: >> Hi Srdjan, >> >> We're looking into re-purposing UmTRX for LTE and there a few things >> which >> we need to understand better. >> >> 1. Is it possible to support 15MHz and 20MHz LTE channel bandwidths? >> To >> achieve this we at least need to sample at 23.04Msps and 30.72Msps >> respectively. LMS6002D datasheet specifies the maximum I/Q samplerate >> of >> 14Msps, which is not enough. But at the same time, datasheet claims >> that ADC >> and DAC are specified up to 50Msps. How does this fits together? > > Alexander, > Can you provide a reference to where the datasheet calls out a max I/Q > sample rate of 14 Msps? The analog low pass filters support a max > bandwidth of 14 MHz (which leads to 28 MHz RF bandwidth assuming > zero-IF operation)...is this what you're referencing? The datasheet is not very clear on this topic. I'm referring to the following line at the Table 1: Baseband Bandwidth 14MHz Originally I read this line as "digital I/Q bus has limitation of 14Msps" and this is what confuses me.

> We run the A/D > converters in the LMS6002d at sample rates greater than 14 Msps all > the time, including 30.72 Msps. Just to be sure - do you mean you feed RX_CLK and TX_CLK of LMS6002D with 61.44MHz clock? It's divided by 2 internally, so if you feed them with 30.72MHz clock you actually get only 15.36Msps out of LMS6002D.