ADF4368 datasheet(21/54 Pages) AD

21 / 54 page

Data Sheet

ADF4368

THEORY OF OPERATION

analog.com

Rev. 0 | 21 of 54

Output Invert (INV_CLKOUT)

The output invert (INV_CLKOUT) is used to shift the output signal

180°. INV_CLKOUT is located inside the PLL loop. Any change

to INV_CLKOUT results in the PLL losing lock for few loop time

constants. Use the INV_CLKOUT bit found in register REG0011 to

directly program the output phase.

Feedback Divider (N)

The feedback divider allows a division ratio in the PLL feed-

back path. Determine the division ratio by the N_INT bit fields,

Bits[11:0] (REG0011 and REG0010), the FRAC1WORD bit fields,

Bits[24:0] (REG0015, REG0014, REG0013, and REG0012), the

FRAC2WORD bit fields, Bits[23:0] (REG0019, REG0018, and

REG0017), and the MOD2WORD bit fields, Bits[23:0] (REG001C,

REG001B, and REG001A) values that this divider comprises to-

gether with the fixed modulus MOD1WORD, which is equal to 225.

The 24-bit variable MOD2WORD and the 25-bit fixed MOD1WORD

forms a 49-bit combined fractional modulus. For the relationship be-

tween the N_INT bit fields, Bits[11:0], the FRAC1WORD bit fields,

Bits[24:0], MOD1WORD, the FRAC2WORD bit fields, Bits[23:0],

the MOD2WORD bit fields, Bits[23:0], and the CLKOUT_DIV bits,

together with R, D, and the fREF, fPFD, fVCO, and fOUT frequencies,

see the Output Frequency section.

RF Output Buffer

Figure 42. Simplified RF Output Buffer Schematic

The low noise, differential output buffer in Figure 42 a differential

output voltage. The output amplitude level and common mode volt-

age are settable with the CLK1_OPWR bits and the CLK2_OPWR

bits. Each output can be either AC-coupled or DC-coupled and

terminated with 100 Ω differentially. If a single-ended output is

desired, each side of the output must be individually AC-coupled

and terminated with 50 Ω.

The lowest four CLKx_OPWR settings can be used without any

external pull-up inductor. External inductors are required to achieve

the higher output power. A 3.4 nH 0302 package or smaller inductor

is recommended. For more details on the evaluation board sche-

matic, refer to the EVAL-ADF4368 user guide.

ADF4368 Datasheet(PDF) 21 Page - Analog Devices