AD9175 datasheet(59/150 Pages) AD

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Data Sheet

AD9175

Rev. A | Page 59 of 150

NCO ONLY MODE

The AD9175 NCOs can operate in standalone mode, where the

JESD204B link is disconnected (or disabled) and one or more NCO

tones are output from DAC0 and/or DAC1. The correct JESD204B

mode must still be selected to configure the corresponding

channelizer and/or main datapath clock domains. In NCO only

mode, a single-tone sine wave is generated by each NCO by

modulating the NCO output with dc samples that are generated

internally. The amplitude of the dc samples directly corresponds

to the amplitude of the NCO tone output by the DAC core. All

NCOs are modulated by the same set of dc samples and, therefore,

their amplitude cannot be independently controlled as shown in

Figure 82. If independent amplitude control is desired, consider

establishing a JESD204B link to provide dc samples from an

external data source.

The data source of the digital datapaths in NCO only mode is the

dc data word, meaning that whether the JESD204B link is

initially brought up or not, the data from the link is not passed

to the datapaths. However, the input to the datapaths is easily

switched between the dc data input and SERDES block input, by

either Register 0x130 or Register 0x1E6, depending on the data-

path. The connection can be made on-the-fly, assuming that a

JESD204B link is previously configured and proper data samples

are supplied. During the transition, sensitive external components

can be protected using the PA protection block as described

previously.

To use any of the NCOs in NCO only mode, the user can elect to

configure the AD9175 to operate in JESD204B Mode 0, Mode 1,

or Mode 2, depending on the desired number of channel NCOs.

Any other JESD204B mode can be selected instead, as long as

the NCO is not bypassed (interpolation = 1). To enable the

NCOs that connect to DAC1, a dual-link JESD204B mode can

be configured. It is not necessary to establish the JESD204B link

with an external source, such as an FPGA, and instead only a few

SPI register writes are needed to enable the necessary JESD204B

mode, to set up the clock domains corresponding to each NCO.

In general, NCO only mode is a useful to bring up a transmitter

radio signal chain without requiring a digital data source initially,

or in applications where a sine wave output is all that is required

(also known as DDS mode), such as in LO or radar applications.

There is an additional optional calibration NCO block that can

be used as part of the initial system calibration without otherwise

making changes to the configuration of the digital datapath.

MODULATOR SWITCH

For added flexibility, the final NCO block (NCO0 and NCO1,

to correspond to the DAC core they feed by default, in

Configuration 0) includes a modulator switch that allows the

user to route the desired I and/or Q sample to one or all DAC

cores. NCOx are located near the output of their respective

main digital datapaths. The switch has four configurations, as

shown in Figure 83 through Figure 86.

DAC

CORE

PA PROTECT

RAMP

UP/DOWN

GAIN

NCO

CALIBRATION

32-BIT NCO

REG 0x1E2 TO REG 0x1E5

MAIN 48-BIT

NCO

REG 0x114 TO REG 0x119

NCO

DDSC_EN_DC_INPUT

REG 0x130, BIT 0

NCO

DC AMPLITUDE LEVEL

(REG 0x148 TO REG 0x149)

CHANNEL

GAIN

CHANNEL

GAIN

CHANNEL

GAIN

DDSM_EN_CAL_DC_INPUT

REG 0x1E6, BIT 1

DDSM_EN_CAL_ACC

REG 0x1E6, BIT 2

DDSM_EN_CAL_FREQ_TUNING

REG 0x1E6, BIT 0

DDSC_EN_DC_INPUT

REG 0x130, BIT 0

DDSC_EN_DC_INPUT

REG 0x130, BIT 0

Figure 82. DC Amplitude Injection for NCO Only Mode Block Diagram

NCO

DAC0 I DATA

DAC0 NCO REAL DATA

TO DAC0 CORE

DAC0 Q DATA

NCO

DAC1 I DATA

DAC1 NCO REAL DATA

TO DAC1 CORE

DAC0 MOD SWITCH CONFIGURATION

DAC1 MOD SWITCH CONFIGURATION

DAC1 Q DATA

Figure 83. Configuration 0—DAC0 = I0, DAC1 = I1

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