AD9166 datasheet(52/138 Pages) AD

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AD9166

Data Sheet

Rev. 0 | Page 52 of 138

NORMALIZED FREQUENCY (Rad/Sample)

–140

–120

–100

–80

–60

–40

–20

Figure 74. Fourth 2× Half-Band 11.25% Filter Response

NORMALIZED FREQUENCY (Rad/Sample)

–140

–120

–100

–80

–60

–40

–20

Figure 75. FIR85 2× Half-Band 45% Filter Response

DIGITAL MODULATION

The AD9166 has digital modulation features to modulate the

baseband quadrature signal to the desired DAC output

frequency.

The AD9166 is equipped with several NCO modes. The default

NCO is a 48-bit, integer NCO. The A/B ratio of the dual-modulus

NCO allows the output frequency to be synthesized with very

fine precision. NCO mode is selected, as shown in Table 35.

Table 35. Modulation Mode Selection

Modulation Mode

Modulation Type

Bit 6

Bit 2

None

0b0

48-Bit Integer NCO

0b1

0b0

48-Bit Dual-Modulus NCO

0b1

32-Bit FFH NCO1

0b1

1 The FFH NCOs are enabled by writing a nonzero word to their frequency

tuning word registers when the main 48-bit NCO is enabled (see the Fast

Frequency Hopping (FFH) section). The modulus can be enabled or disabled.

If the modulus is enabled, the same modulus ratio applies to all the NCOs.

48-Bit Dual Modulus NCO

This modulation mode uses an NCO, a phase shifter, and a

complex modulator to modulate the signal by a programmable

carrier signal as shown in Figure 76. This configuration allows

output signals to be placed anywhere in the output spectrum

with very fine frequency resolution.

The NCO produces a quadrature carrier to translate the input

signal to a new center frequency. A quadrature carrier is a pair of

sinusoidal waveforms of the same frequency, offset 90° from

each other. The frequency of the quadrature carrier is set via an

FTW. The quadrature carrier is mixed with the I and Q data and

then summed into the I and Q datapaths, as shown in Figure 76.

Integer NCO Mode

The main 48-bit NCO can be used as an integer NCO by using

the following formula to create the FTW:

−fCLK/2 ≤ fCARRIER < + fCLK /2

FTW = (fCARRIER/fCLK) × 248

where:

fCARRIER is the carrier frequency.

FTW is a 48-bit, twos complement number.

When in 2× NRZ mode (FIR85 enabled with Register 0x111,

Bit 0 = 1), the frequency tuning word is calculated as

0 ≤ fCARRIER < fCLK

FTW = (fCARRIER/fCLK) × 248

where FTW is a 48-bit binary number.

This method to calculate the FTW for 2× NRZ mode allows the

tone to correctly move from 0 Hz toward fCLK when the FTW is

incremented. Use this method only for 2× NRZ mode. If the

desired tone is placed between fCLK/2 and fCLK and the FIR85

enable bit is set to 0b0 without adjusting the FTW, the tone may

appear to change location to a new frequency.

The FTW is set as shown in Table 36.

Table 36. NCO FTW Registers

Address

Value

Description

0x114

FTW[7:0]

8 LSBs of FTW

0x115

FTW[15:8]

Next 8 bits of FTW

0x116

FTW[23:16]

Next 8 bits of FTW

0x117

FTW[31:24]

Next 8 bits of FTW

0x118

FTW[39:32]

Next 8 bits of FTW

0x119

FTW[47:40]

8 MSBs of FTW

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