AD9549 datasheet(69/78 Pages) AD

69 / 78 page

Preliminary Technical Data

AD9549

Rev. PrA | Page 69 of 78

0106; S Divider (continued)

[0] Divide by 2: Setting this bit enables an additional /2 pre-scalar. See “Feedback Divider (Divide-by-S)” on Page 23. If the

desired feedback ratio is greater than 65536, or if the feedback signal on FDBK_IN is greater than 400 MHz, then this bit must

be set. An example of this case is when the PLL is locking to an image of the DAC output that is above the Nyquist frequency.

[6:1] Unused

[7] Falling Edge Triggered: Setting this bit inverts the reference clock before the S divider.

Digital PLL Loop Filter

0107; P Divider

[4:0] Divide Ratio: Controls the ratio of DAC sample rate to loop filter sample rate. See “Digital Loop Filter” on Page 24.

Loop filter sample rate = DAC Sample rate / 2^(Divide Ratio[4:0]). For the default case of 1 GHz DAC sample rate, and

P Divider [4:0] of 5, the loop filter sample rate is 31.25 MHz. Note: The DAC sample rate is the same as System Clock.

0108 – 0109; Loop Coefficients (See ”Digital Loop Filter Coefficients” on Page 28.)

(Note : The AD9549 evaluation software will derive these values.)

[11:0] Alpha-0: Linear coefficient for “alpha” coefficient

010A; Loop Coefficients (continued)

[4:0] Alpha-1: Power of 2 multiplier for “alpha” coefficient

010B; Loop Coefficients (continued)

[3:0] Alpha-2: Power of 2 divider for “alpha” coefficient

010C – 010D; Loop Coefficients (continued)

[11:0] Beta-0: Linear coefficient for “beta” coefficient

010E; Loop Coefficients (continued)

[2:0] Beta-1: Power of 2 divider for “beta” coefficient

010F – 0110; Loop Coefficients (continued)

[11:0] Gamma-0: Linear coefficient for “gamma” coefficient

0111; Loop Coefficients (continued)

[2:0] Gamma -1: Power of 2 divider for “gamma” coefficient

0112 – 0114; Reserved

0115 – 011A; FTW Estimate (Read-Only)

[47:0] FTW Estimate: This is frequency estimate from frequency estimator circuit, and is informational only. It’s useful for

verifying the input reference frequency. See “Frequency Estimator“ on Page 47 for a description.

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