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ADC12J1600 Datasheet(PDF) 37 Page - Texas Instruments |
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ADC12J1600 Datasheet(HTML) 37 Page - Texas Instruments |
37 / 98 page ![]() 25 2 N NCO _ FREQ round NCO _ RDIV § · u u ¨ ¸ ¨ ¸ © ¹ (NCO) (STEP) ¦ N ¦ 25 2 N NCO _ FREQ round NCO _ RDIV § · u u ¨ ¸ ¨ ¸ © ¹ (DEVCLK) (STEP) ¦ ¦ NCO _ RDIV 128 § · ¨ ¸ ¨ ¸ © ¹ ADC12J1600, ADC12J2700 www.ti.com SLAS969C – JANUARY 2014 – REVISED JULY 2015 7.3.6.2.4 NCO Frequency Setting (Eight Total) 7.3.6.2.4.1 Basic NCO Frequency-Setting Mode In basic NCO frequency-setting mode, the NCO frequency setting is set by the 32-bit register value, NCO_FREQn (n = preset 0 trough 7, see the NCO Frequency (Preset x) Register section). (n = 0 – 7) ƒ(NCO) = NCO_FREQn × 2 –32 × ƒ (DEVCLK) (3) NOTE Changing the register setting after the JESD204B interface is running results in non- deterministic NCO phase. If deterministic phase is required, the JESD204B link must be re-initialized after changing the register setting. See the Multiple ADC Synchronization section. 7.3.6.2.4.2 Rational NCO Frequency Setting Mode In basic NCO frequency mode, the frequency step size is very small and many frequencies can be synthesized, but sometimes an application requires very specific frequencies that fall between two frequency steps. For example with ƒS equal to 2457.6 MHz and a desired ƒ(NCO) equal to 5.02 MHz the value for NCO_FREQ is 8773085.867. Truncating the fractional portion results in an ƒ(NCO) equal to 5.0199995 MHz, which is not the desired frequency. To produce the desired frequency, the NCO_RDIV parameter is used to force the phase accumulator to arrive at specific frequencies without error. First, select a frequency step size (ƒ(STEP)) that is appropriate for the NCO frequency steps required. The typical value of ƒ(STEP) is 10 kHz. Next, program the NCO_RDIV value according to Equation 4. (4) The result of Equation 4 must be an integer value. If the value is not an integer, adjust either of the parameters until the result in an integer value. For example, select a value of 1920 for NCO_RDIV. NOTE NCO_RDIV values larger than 8192 can degrade the NCO SFDR performance and are not recommended. Now use Equation 5 to calculate the NCO_FREQ register value. (5) Alternatively, the following equations can be used: (6) (7) Copyright © 2014–2015, Texas Instruments Incorporated Submit Documentation Feedback 37 Product Folder Links: ADC12J1600 ADC12J2700 |
Similar Part No. - ADC12J1600_16 |
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Similar Description - ADC12J1600_16 |
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