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AD9174

Data Sheet

Rev. A | Page 52 of 164

DIGITAL DATAPATH

The AD9174 has two independent digital datapaths, each

typically supplying data samples to the respective DACx core.

However, there are modulator switch configurations that allow

additional ways to route the samples to either DAC0, DAC1, or

both DACs. See the Modulator Switch section for more details.

Each digital datapath consists of multiple channel datapaths

(channelizers) that sum into a single datapath (main datapath),

which in turn connects to its respective DAC core by default

(see Figure 1). The channelizers and the main datapaths are

fully bypassable, depending on the JESD204B mode selected by

the user. There are a variety of digital processing blocks

available within the channelizers and the main datapaths,

including interpolation filters, bypassable NCOs that allow

either digital I/Q modulation of samples or standalone (DDS)

operation, PA protection blocks (power detection and

protection (PDP) block), and digital gain blocks to ramp or set

the sample gain.

TOTAL DATAPATH INTERPOLATION

The AD9174 contains two stages of interpolation filters: one

stage is located within each channel datapath and is set to a single

value across all channels, and one stage is located within each main

datapath. The total interpolation for a complete digital datapath

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 interpolation filters

covers 80% of the total bandwidth (BW) occupied by the incoming

data. Therefore, if using interpolation (total interpolation > 1), the

available signal BW is 80% of the data rate. If the interpolation

stages are bypassed (total interpolation = 1), the available signal

BW is 50% of the data rate because complex data is not used.

The signal bandwidth is calculated as follows:

Signal BW = 0.8 × fDATA, if total interpolation > 1

Signal BW = 0.5 × fDATA, if total interpolation = 1

The interpolation values are programmed as shown in the Table 34.

Table 34. Interpolation Factor Register Settings

Interpolation

Factor

Main Datapath,

Bits[7:4]

Channel Datapath,

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)

0.5 × fDATA

fDAC

2×, 4×, 6×, 8×, 12×,

16×, 18×, 24×,

32×, 36×, 48×, 64×

0.8 × fDATA

fDAC/total interpolation

Filter Performance

The interpolation filters interpolate the incoming data samples

so that changes in the incoming data are minimized, while

suppressing any 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 70 and Figure 71. The maximum

pass-band amplitude of all filters is the same. In Figure 70 and

Figure 71, the amplitudes are intentionally shown to be different

to improve understanding, and in reality the amplitude across

all filters is constant and uniform regardless of the interpolation

rate selected by the user.

–2000

–1000

1000

2000

3000

4000

FREQUENCY (MHz)

1× (MAX DAC = 6GHz)

2× (MAX DAC = 8GHz, 12 BITS)

2× (MAX DAC = 6GHz, 16 BITS)

4× (MAX DAC = 12GHz)

6× (MAX DAC = 12GHz)

Figure 70. Band Responses of Total Interpolation Rates for 1×, 2×, 4×, and 6×

at Each Respective Maximum Achievable DAC Rate and Resolution

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