AD9173 datasheet(56/144 Pages) AD

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Data Sheet

AD9173

DIGITAL DATAPATH

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Rev. C | 56 of 144

Table 42. PDP Threshold and Power Calculation Controls

Bits

Control

0x583

[7:0]

LONG_PA_THRESHOLD[7:0]

0x584

[4:0]

LONG_PA_THRESHOLD[12:8]

0x586

[7:0]

LONG_PA_POWER[7:0]

0x587

[4:0]

LONG_PA_POWER[12:8]

0x588

[7:0]

SHORT_PA_THRESHOLD[7:0]

0x589

[4:0]

SHORT_PA_THRESHOLD[12:8]

0x58B

[7:0]

SHORT_PA_POWER[7:0]

0x58C

[4:0]

SHORT_PA_POWER[12:8]

Main Datapath Interpolation

The main digital datapath interpolation options available are bypass

(1×), 2×, 4×, 6×, 8× and 12×. Each of the half-band filters used

for interpolation have 80% bandwidths with 85 dB of stop band

rejection. The channel half-band cascaded configuration is shown

in Figure 75, with each of the useable bandwidths of the channel

interpolation filters listed in Table 43.

Figure 75. Main Datapath Interpolation Half-Band Filter Block Diagram

Table 43. Main Datapath Interpolation Useable Bandwidths and Rejection

Half-Band Filter

Bandwidth

(×fIN_FILTER)

Stop Band Rejection (dB)

HB3

80%

HB4

40%

TB1

27%

HB5

20%

Main Digital Modulation

The AD9173 has digital modulation features to modulate the base-

band quadrature signal to a desired frequency. There are two

stages of complex digital modulation available in the AD9173; chan-

nel modulation and main modulation. Each main DAC has a final

main NCO that can individually modulate each main DAC datapath

with a unique frequency and phase offset. The AD9173 is equipped

with several NCO modes. The default NCO is a 48-bit, integer

NCO. There is an additional modulus option for each main DAC

datapath NCO where 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 44. These controls are

paged per the main DAC page masks, MAINDAC_PAGE (Register

0x008, Bits [7:6]).

Table 44. Main Modulation Mode Selection

Modulation Mode

Modulation Type

None

0b0

48-Bit Integer NCO

0b1

0b0

Table 44. Main Modulation Mode Selection

Modulation Mode

Modulation Type

48-Bit Dual Modulus NCO

0b1

The main NCO blocks also contain sideband selection controls as

well as options for how the FTW and phase offset controls are

updated.

Calculate the phase offset word control as follows:

−180° ≤ Degrees Offset ≤ +180°

Degrees Offset = 180° × (DDSM_NCO_PHASE_OFFSET/215)

where DDSM_NCO_PHASE_OFFSET is a 16-bit twos complement

value programmed in the registers listed in Table 45.

Table 45. Main Datapath NCO Phase Offset Registers

Address

Value

Description

0x11C

DDSM_NCO_PHASE_OFFSET[7:0]

8 LSBs of phase offset

0x11D

DDSM_NCO_PHASE_OFFSET [15:8] 8 MSBs of phase offset

48-Bit Dual Modulus NCO

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

plex modulator to modulate the signal by a programmable carrier

signal, as shown in Figure 71. This configuration allows output

signals to be placed anywhere in the output spectrum up to ±fNCO/2

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 a 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 71.

Integer NCO Mode

The channel 48-bit NCOs can be used as integer NCOs. The FTW

for the channel NCOs depends on the speed at which the main

NCO block is running (fDAC), which is the same rate as the DAC

sample rate (12.6 GSPS, maximum) and can be calculated by

using the following formula:

fDAC = fDATA × Channel Interpolation × Main Interpolation

The FTWs for each individual channel can be programmed sepa-

rately and are calculated using the following formula:

−fDAC/2 ≤ fCARRIER < +fDAC/2

DDSM_FTW = (fCARRIER/fDAC) × 248

where DDSM_FTW is a 48-bit, twos complement number.

The frequency tuning word is set as shown in Table 46.

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