AD9860 datasheet(21/32 Pages) AD

21 / 32 page

REV. 0

AD9860/AD9862

–21–

In most systems, the DAC (and each up-converter stage) requires

analog filtering to meet spectral mask and out-of-band spurious

emissions requirements. Digital interpolation (Block C) and

Hilbert filtering (Block E) can be used to relax some of the system

analog filtering.

Digital 2

interpolation with input data rates of up to 64 MSPS or

interpolation with input data rates of 32 MSPS is available

in this mode (or interpolation filters can be bypassed to achieve

a 128 MSPS input data rate). The data bandwidth with 2

interpolation enabled is up to 38% of the input data rate. If

no interpolation is enabled, the data bandwidth will be the full

Nyquist band with Sinc

limitations. The interpolation filters

are configured through the Interpolation Serial register.

The Hilbert filter can be enabled in this mode to suppress the

positive or negative image that naturally occurs with real data.

The single sideband signal when combined with a quadrature

modulator can upconvert the desired signal and suppressed image,

forming a Hartley Image Rejection Architecture (both Tx paths

need to be enabled to produce the Image Rejection Architecture).

The Hilbert filter will provide over 50 dB image suppression for

signals between 12.5% to 38% of the input data rate. The Hil-

bert filter can be enabled and configured using the Hilbert and

Keep –ve Serial registers.

Digital frequency tuning the Tx output is also possible in this

mode using the coarse modulation block. The coarse modulation

block can be used to frequency shift the Tx signal either –fDAC/4,

–fDAC/8, +fDAC/8 or +fDAC/4. The coarse modulator does not

require the Hilbert filter to be enabled, in which case the real

signal and image will shift. If the Hilbert filter is enabled, a

complex mix can be performed on the single sideband signal by

the coarse modulator (Note: the Hilbert filter does not need to

be enabled if single sideband data is provided externally).

The fine modulator can be used to accurately place the output

signal shifting the Tx data spectrum in the positive or negative

direction with a resolution of fDAC/2

26. The fine modulator

requires both 4

interpolation and the Hilbert filter enabled to

be used in this mode. The coarse modulator and fine modulator

can both be used and provide a tuning range between

±68% of

the DAC Nyquist frequency.

If all Tx DSP blocks are bypassed, the AD9860/AD9862 oper-

ates similar to a standard TxDAC. In Single Channel DAC Data

mode, only the Channel A DAC is used; Channel B is powered

down to reduce power consumption.

Two Independent Real Signal DAC Data

The Dual Channel Real DAC Data mode is used to transmit

diversity or dual channel signals. In this mode, 12-/14-bit, dual

channel, interleaved Tx data is provided to the AD9860/AD9862

and latched using either CLKOUT1 or CLKOUT2 edges as

defined in the Clock Overview section of the data sheet. Both

Tx paths are enabled and the two signals will be processed

independently. The Tx digital processing blocks available in this

mode are the Interpolation Filters (Block C) and the Coarse

Modulator (Block D).

As mentioned previously, the interpolation filters can be used to

relax requirements on the external analog filters. The maximum

rate of the Tx interface is 128 MSPS, i.e., 64 MSPS/channel

with interleaved data. Therefore to fully take advantage of the

DACs maximum update rate of 128 MSPS, 2

interpolation is

required. The 4

interpolation filter is recommended for input

data rates equal to or less than 32 MSPS/channel (64 MSPS

interleaved). The data bandwidth with 2

or 4

interpolation

enabled is up to 37.5% of the channel input data rate. If no

interpolation is enabled, the data bandwidth will be the full

Nyquist band with Sinc

limitations. The interpolation filters

are configured through the Interpolation Serial register.

The coarse modulation will perform a real mix of each channel,

independently, with either fDAC/4 or fDAC/8.

Dual Channel Complex DAC Data

The Dual Channel Complex DAC Data (also known as Single

Sideband Data) is used to generate complex Tx signals (i.e., I and

Q). In this mode, 12-/14-bit, interleaved I and Q data is provided

to the AD9860/AD9862 and latched using either CLKOUT1 or

CLKOUT2 edges as defined in the Clock Overview section of

the data sheet. Both Tx paths are enabled and the two signals

will be processed as a complex waveform. The Tx digital pro-

cessing blocks available in this mode are the Fine Modulator

(Block B), the Interpolation Filters (Block C), and the Coarse

Modulator (Block D).

As mentioned previously, the interpolation filters can be used to

relax requirements on the external analog filters. The maximum

rate of the Tx interface is 128 MSPS, i.e., 64 MSPS/channel with

interleaved data (as is the case in this mode). Therefore, to fully

take advantage of the DAC’s maximum update rate of 128 MSPS,

interpolation is required. The 4

interpolation is recommended

for input data rates equal to or less than 32 MSPS/channel

(64 MSPS interleaved). The data bandwidth with 2

or 4

interpolation enabled is up to 37.5% of the channel input data

rate. If no interpolation is enabled, the data bandwidth will be

the full Nyquist band with Sinc

limitations. The interpolation

filters are configured through the Interpolation Serial register.

A complex mix can be performed on the single sideband signal

by the coarse and/or fine modulator. The coarse modulation

block can be used to frequency shift the Tx signal either –fDAC/4,

–fDAC/8, +fDAC/8 or + fDAC/4. The fine modulator can be used to

accurately place the output signal shifting the Tx data spectrum

in the positive or negative direction with a resolution of 1/2

26 of

the DAC update rate. The fine modulator requires 4

interpola-

tion to be enabled. The coarse modulator and fine modulator

can both be used and provide a tuning range between

±70% of

the DAC Nyquist frequency.

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