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Data Sheet

AD9173

DIGITAL DATAPATH

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Rev. C | 49 of 144

The full digital datapath of the AD9173 consists of channel data-

paths that are bypassable, as well as a main DAC datapath leading

up to the analog DAC core. There is a variety of different digital

feature blocks available within each of the channel and main DAC

datapaths.

TOTAL DATAPATH INTERPOLATION

The AD9173 contains two separate blocks of interpolation: one

located in each of the channelizer datapaths, and a second inter-

polation stage located in the main DAC datapath. The total interpo-

lation for the chip can be determined by multiplying the channel

interpolation factor by the main datapath interpolation factor. The

relationship between the DAC sample rate and input data rate is

shown in the following equation:

Total Interpolation = (Channel Interpolation × Main Interpolation)

fDATA = fDAC/(Channel Interpolation × Main Interpolation)

Each of the various cascaded half-band filters has 80% signal

bandwidth capabilities. Therefore, if using interpolation (not bypass

or 1× total interpolation for both channel and main datapaths), the

available signal bandwidth (BW) with respect to the input data rate

is calculated as follows:

SignalBW = 0.8 × (fDATA/2)

where the total interpolation > 1.

SignalBW = (fDATA/2)

where the total interpolation = 1.

The interpolation values are programmed as shown in Table 34.

Table 34. Interpolation Factor Register Settings

Interpolation

Factor

Main Datapath, Register

0x111, Bits[7:4]

Channel Datapath, Register

0x111, Bits[3:0]

1×

0x1

2×

0x2

3×

Not applicable

0x3

4×

0x4

6×

0x6

8×

0x8

12×

0xC

Not applicable

Table 35. Interpolation Modes and Useable Bandwidth

Total Interpolation

Available Signal

Bandwidth

fDATA

1× (Bypass)

fDATA/2

fDAC

2×, 4×, 8×, 12×, 16×, 18×,

24×, 32×, 36×, 48×, 64×

80% × fDATA /2

fDAC/total interpolation

Filter Performance

The interpolation filters interpolate between existing data in such

a way that they minimize changes in the incoming data while

suppressing the creation of interpolation images.

The usable bandwidth, as shown in Table 35 is defined as the

frequency band over which the filters have a pass-band ripple of

less than ±0.001 dB and an image rejection of greater than 85 dB.

Conceptual drawings that shows the relative bandwidth of each of

the filters are shown in Figure 66 and Figure 67. The maximum

pass-band amplitude of all filters is the same; they are different in

the illustration to improve understanding.

Figure 66. Band Responses of Total Interpolation Rates for 1×, 2×, and 4× at

Each Respective Maximum Achievable DAC Rate , 11-Bit Resolution

Figure 67. Band Responses of Total Interpolation Rates for 8×, 12×, 16×, 18×,

24×, 32×, 36×, 48×, and 64× at a 12 GHz DAC Rate, 16-Bit Resolution (Unless

Otherwise Noted)

NCO Only Mode

The AD9173 is capable of operating in a mode with only the NCO

enabled. In this mode, a single-tone sine wave is generated using

a programmable internal dc amplitude level that is injected into the

NCO block to modulate the data into a single tone. This internal dc

level is injected into either the channel or main datapaths through

various controls, as shown in Figure 68. Mode 3 and Mode 4 can

be used to generate a single-channel or dual channel NCO only

mode of operation, respectively. It is not necessary to bring up the

JESD204B link in this mode. This mode is a useful option to bring

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