AD9546SLASHPCBZ datasheet(125/205 Pages) AD

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Data Sheet

AD9546

Rev. 0 | Page 125 of 205

DIGITAL

LOOP

FILTER

DPLL0

FROM

DIGITAL PFD

NCO

LOOP

FILTER

COEFFICIENTS

0 1

FAST

ACQ 0

PHASE LOCK

DETECT

ADJ

DIGITAL

LOOP

FILTER

DPLL1

FROM

DIGITAL PFD

NCO

LOOP

FILTER

COEFFICIENTS

PHASE LOCK

DETECT

LF1

ADJ

FAST

ACQ 1

REG 0x1207 TO 0x1204, BITS[31:0]

REG 0x1203, BIT 7

REG 0x0C17 TO 0x0C0C, BITS[95:0]

REG 0x0C0B TO 0x0C00, BITS[95:0]

LOOP FILTER 0

COEFFICIENTS

LOOP FILTER 1

COEFFICIENTS

NOTES

1. A RANGE OF BITS USES A COLON SEPARATOR

2. EXCEPT FOR LF0 AND LF1, REGISTER ADDRESSES ARE SPECIFIC TO TRANSLATION PROFILE 0.0 AND 1.1

0 1

REG 0x1603, BIT 7

REG 0x1607 TO 0x1604, BITS[31:0]

REG 0x160F TO 0x160C, BITS[31:0]

REG 0x120F TO 0x120C, BITS[31:0]

LF0

Figure 90. Digital Loop Filter Block Diagram

DPLL Loop Filter Bandwidth

Because the base coefficients establish a normalized frequency

response, the loop filter requires a scale factor to set the

absolute frequency response. The scale factor, which sets the

bandwidth (BW), resides in the translation profiles (see the

Translation Profiles section), as shown in Figure 90. The scale

factor is Bits[31:0] (unsigned) residing in the appropriate

translation profile at the start address shown in Table 74 plus an

offset of 4 to 7 (decimal).

The frequency units associated with the scale factor depend on the

normalization of the LF0 and LF1 base coefficients (see the DPLL

Loop Filter Base Coefficients section). In the case of the default

base coefficients, the normalized frequency units are µHz

(10−6 Hz) for both LF0 and LF1.

To calculate the scale factor necessary to set the 0 dB open-loop

bandwidth, divide the desired loop bandwidth by the

normalized frequency associated with the selected set of base

coefficients, LF0 or LF1. In the case of the default LF0 and LF1

values, the normalized frequency is 10−6 Hz.

For example, given a desired loop bandwidth of 50 Hz, the

required scale factor is

Scale Factor = 50 Hz/10−6 Hz

= 50,000,000

= 0x 02FA F080 (hexadecimal)

Note that the 32-bit scale factor implies a maximum DPLL loop

bandwidth of nearly 4.3 kHz (232 × 10−6 Hz). However, the

presence of the NCO gain tuning word filter in the loop (see the

NCO Gain Tuning Word Filter Bandwidth section) puts a

constraint on the maximum DPLL loop filter bandwidth. Table 80

relates the maximum DPLL loop filter bandwidth as a function of

the value of the selected NCO gain filter bandwidth. The active

translation profile of the DPLL determines whether the LF0 or

LF1 column applies for a given DPLL channel.

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