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From: | Marcus Müller |
Subject: | Re: [Discuss-gnuradio] USRP phase to sample index relation in the DDC/DUC chain |
Date: | Mon, 3 Jul 2017 21:02:18 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 |
Hello Nicolas, sorry for the delayed reaction! So, the signal chain looks roughly like this: RX: ADC (@Master Clock Rate (MCR) --> Rotator (@MCR) -->
decimator --> Host (@user-requested sampling rate) TX: Host (@user sampling rate) --> interpolator --> Rotator (@MCR) --> DAC (@MCR) The two rotators here are the CORDICs you're referring to. UHD just calculates by how much of the master clock rate you need to rotate per sample – e.g. if you tune digitally by 1 MHz, and your MCR is 200 MHz, then each sample needs to be phase-shifted by ; ie. you need a multiplicator that takes the input sample, and multiplies it with a complex factor ; and after each sample, that needs to be incremented by . Thus, what UHD calculates is exactly that factor of 2π/200 and sends it to the CORDIC unit on the FPGA, which then uses that value as phase increase. Best regards, Marcus On 06/09/2017 11:04 AM, Nicolas GALLAND
wrote:
Hello everyone, |
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