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AD9175

Data Sheet

Rev. A | Page 52 of 150

CHANNEL DIGITAL DATAPATH

2×

3×

TO MAIN

DATAPATH

NCO

DIGITAL

GAIN

1×

2×

3×

NCO

DIGITAL

GAIN

2×

3×

NCO

DIGITAL

GAIN

Figure 74. Block Diagram of the Channel Digital Datapath per the Main DAC Output

Whether one or all of the channelizers in each datapath are

enabled is defined by the JESD204B mode selected by the

user. Each channelizer consists of a digital gain stage, complex

interpolation block, and a complex 48-bit modulus NCO. The

channelizers and the summing node can be fully bypassed (1×

interpolation selected). The interpolation rate selection is applied to

all channelizers and cannot be independently controlled.

However, the gain stage and complex NCO settings can all be

controlled independently. 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. The

channelizers can be either paged individually to apply settings

that are unique to a specific channel, or can be paged as a group

to address multiple channelizers using a single set of SPI writes.

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

Each channelizer has an independent gain control that allows

unique gain scaling for each complex data stream. The gain

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

by the following formula:

0 ≤ Gain ≤ (212 − 1)/211

−∞ dB < dB Gain ≤ +6.018 dB

Gain = Gain Code × (1/2048)

dB Gain = 20 × log10 (Gain)

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

The gain code control (CHNL_GAIN) is paged with the

channel page mask (CHANNEL_PAGE) in Register 0x008,

Bits[5:0].

Because the output of all three channels is summed ahead of the

main datapath, extra care must be used when setting the gain to

avoid sample clipping if the combined amplitude exceeds full

scale after being summed. For example, if all three channels are

used and all three data streams contain samples that are >1/3

full scale, clipping may occur. In other words, at any specific

point in time, the sum of the samples at the output of all

enabled channels must be between −215 and +(215 − 1).

The digital gain feature is available in all JESD204B modes,

except when 1× channel interpolation is used because the

channel digital processing features are bypassed in that mode,

as shown in Figure 75.

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