AD9172 datasheet(52/146 Pages) AD

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Data Sheet

AD9172

DIGITAL DATAPATH

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Rev. C | 52 of 146

CHANNEL DIGITAL DATAPATH

Figure 65. Block Diagram of the Channel Digital Datapath per the Main DAC Output

Each main DAC output has three optional channelizers, or channel

datapaths, that are selected based on the JESD204B mode select-

ed. The channel datapaths also have the option to be bypassed

(1× interpolation selected), which bypasses all of the digital features

included in each channelizer. Each channelizer consists of a digital

gain stage, complex interpolation block, and complex 48-bit NCO

with modulus. The interpolation selection is the same for all three

channelizers; however, the gain stage and complex NCO values

can all be independently configured. The controls for these blocks

are paged by the channel paging mask in the CHANNEL_PAGE

bits (Register 0x008, Bits[5:0]), as described in Table 36. Each bit of

the page mask corresponds to a channel datapath. These channels

can be paged individually to set the values for each channel

uniquely, or can be paged simultaneously to set all channels to the

same value for the control being configured.

Table 36. Channel Page Mask

CHANNEL_PAGE

(Register 0x008,

Bits[5:0])

Channel Paged

Channel Datapath Updated

0x01 (Bit 0)

Channel 0

Channel 0 of DAC0

0x02 (Bit 1)

Channel 1

Channel 1 of DAC0

0x04 (Bit 2)

Channel 2

Channel 2 of DAC0

0x08 (Bit 3)

Channel 3

Channel 0 of DAC1

0x10 (Bit 4)

Channel 4

Channel 1 of DAC1

0x20 (Bit 5)

Channel 5

Channel 2 of DAC1

Each of the digital blocks in the channels is described in more detail

in the following sections.

Digital Gain

The AD9172 has individual channel gain controls that allow unique

gain scaling capabilities for each complex data input channel. The

gain code for each channel is 12-bit resolution, located in Register

0x146 and Register 0x147, and can be calculated by the following

formula:

0 ≤ Gain ≤ (212 − 1)/211

−∞ dB < dBGain ≤ +6.018 dB

Gain = Gain Code × (1/2048)

dBGain = 20 × log10 (Gain)

Gain Code = 2048 × Gain = 211 ×10(dBGain/20)

The gain code control (CHNL_GAIN) is paged with the channel

page mask (CHANNEL_PAGE) in Register 0x008, Bits[5:0]. The

digital gain feature is available in all modes, except when 1×

channel interpolation is used because the channel datapaths are

bypassed in that mode. The summing node that combines the three

channels may clip the summed signals if the combined amplitude

is too large. For example, if all three channels are being used and

all three data streams are >1/3 full-scale amplitude, clipping may

occur. The sum of the data values when any number of channels is

used must be between −215 and +215.

Channel Interpolation

The channel interpolation options available are bypass (1×), 2×, 3×,

4×, 6×, and 8×. Each of the half-band filters used for interpolation

has 80% bandwidths with 85 dB of stop band rejection. The chan-

nel half-band cascaded configuration is shown in Figure 66, with

each of the useable bandwidths of the channel interpolation filters

listed in Table 37.

Figure 66. Channel Interpolation Half-Band Filter Block Diagram

Table 37. Channel Interpolation Useable Bandwidths and Rejection

Half-Band Filter

Bandwidth (×fIN_FILTER)

(%)

Stop Band Rejection (dB)

HB0

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