AD9136-EBZ datasheet(65/117 Pages) AD

65 / 117 page

Data Sheet

AD9135/AD9136

Rev. C | Page 65 of 117

DIGITAL DATAPATH

Figure 73. Block Diagram of Digital Datapath

The block diagram in Figure 73 shows the functionality of the

digital datapath (all blocks can be bypassed). The digital processing

includes three half-band interpolation filters, an inverse sinc filter,

and gain, offset, and group delay adjustment blocks.

Note that the pipeline delay changes when digital datapath

functions are enabled/disabled. If fixed DAC pipeline latency

is desired, do not reconfigure these functions after initial

configuration.

DAC PAGING

Digital datapath registers are paged to allow configuration of

either DAC independently or both simultaneously. Table 60 shows

how to use the DAC paging bits.

Table 60. Paging Modes

DAC_PAGE, Register 0x008[1:0]

DACs Paged

DAC0

DAC1

3 (default)

DAC0 and DAC1

Several functions are paged by DAC, such as input data format,

downstream protection, interpolation, inverse sinc, digital gain,

dc offset, group delay, datapath PRBS, and LMFC sync.

DATA FORMAT

BINARY_FORMAT (Register 0x110[7]), paged as described in

the DAC Paging section) controls the expected input data

format. By default it is 0, which means the input data must be in

twos complement. It can also be set to 1, which means the input

data is in offset binary. For the AD9136, 0x0000 is negative full

scale and 0xFFFF is positive full scale. For the AD9135, 0x0000

is negative full scale and 0xFFE0 is positive full scale.

Though the AD9135 is an 11-bit resolution DAC at the output, the

input to the part must still be 16-bits wide for proper 8-bit/10-bit

decoding. The AD9135 uses a 16-bit datapath that is truncated

to 11 bits before going into the DAC core. Either 11-bit zero-

padded data or full 16-bit data can be sent into the device, with

the latter having slightly better spectral performance by minimizing

quantization error along the datapath.

INTERPOLATION FILTERS

The transmit path contains three half-band interpolation filters,

which each provide a 2× increase in output data rate and a low-

pass function. The filters can be cascaded to provide a 4× or 8×

interpolation ratio. Table 61 shows how to select each available

interpolation mode, their usable bandwidths, and their

maximum data rates. Note that fDATA = fDAC/Interpolation Factor.

Interpolation mode is paged as described in the DAC Paging

section. Register 0x030[0] is high if an unsupported

interpolation mode is selected.

Table 61. Interpolation Modes and Usable Bandwidth

Interpolation

Mode

INTERP_MODE,

Reg. 0x112[2:0]

Usable

Bandwidth

Maximum

fDATA (MHz)

1× (bypass)1

0x00

0.5 × fDATA

21202

2×

0x01

0.4 × fDATA

10602

4×

0x03

0.4 × fDATA

700

8×

0x04

0.4 × fDATA

350

1 Mode 8 and Mode 11 can only use 1× interpolation. 2×, 4×, and 8×

interpolation are only available in Mode 9, Mode 10, Mode 12, and Mode 13.

2 The maximum speed for 1× and 2× interpolation is limited by the JESD204B

interface. See Table 4 for the appropriate supply levels.

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. This is

shown for each filter in Figure 74.

The usable bandwidth (as shown in Table 61) 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.

Figure 74. All Band Responses of Interpolation Filters

Filter Performance Beyond Specified Bandwidth

The interpolation filters are specified to 0.4 × fDATA (with pass

band). The filters can be used slightly beyond this ratio at the

expense of increased pass-band ripple and decreased interpolation

image rejection.

INTERPOLATION

MODES

1×, 2×, 4×, 8×

INV

SINC

DIGITAL GAIN,

DC OFFSET,

AND

GROUP DELAY

ADJUSTMENT

–20

–40

–60

–80

–100

0.2

0.4

0.6

0.8

1.0

FREQUENCY (×

fDAC)

2×

4×

8×

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