DAC38RF83IAAV.B datasheet(64/160 Pages) TI2

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placement between 0 and fDAC/2. The NCOs are enabled by fields NCOAB_ENA and NCOCD_ENA in

FREQ_NCOCD (7.5.26)) and 16-bit phase registers (PHASE_NCOAB (7.5.23) and PHASE_NCOCD (7.5.24))

that generate the sine and cosine terms for the complex mixing. The NCO block diagram is shown in Figure

7-22.

Frequency

Accumulator

RESET

CLK

FDAC

NCO SYNC

via

syncsel_NCO(3:0)

Phase

Look Up

Table

sin

cos

Figure 7-22. NCO Block Diagram

Synchronization of the NCOs occurs by resetting the NCO accumulators to zero. The synchronization source is

selected by fields SYNCSEL_NCOAB and SYNCSEL_NCOCD in register SYNCSEL1 (7.5.29). The frequency

word in the FREQ_NCOAB and FREQ_NCOCD registers are added to the accumulators every clock cycle, fDAC.

The frequency and phase offset of the NCOs are:

NCOAB or CD

u DAC

FREQ

NCOAB or CD

(1)

AB or CD

PHASE

NCOAB or CD

(2)

Treating the complex channels as complex vectors of the form I + j Q, the output of the DQM is:

MIXERAB GAIN

INPUTAB

NCOAB

INPUTAB

NCOAB

Output

cos

ŒI

VLQ

ŒI

(3)

MIXERCD GAIN

INPUTCD

NCOCD

INPUTCD

NCOCD

Output

cos

ŒI

VLQ

ŒI

(4)

Where t is the time since the last resetting of the NCO accumulator and the fields MIXERAB_GAIN and

MIXERCD_GAIN in register MULTIDUC_CFG2 (7.5.13) are either 0 or 1.

The maximum output amplitude of the DQM occurs if IIN(t) and QIN(t) are simultaneously full scale amplitude and

the sine and cosine arguments are equal to an integer multiple of π/4.

With MIXERAB_GAIN or MIXERCD_GAIN = 0, the gain through the DQM is sqrt(2)/2 or -3 dB. This loss in

signal power is in most cases undesirable, and it is recommended that the gain function be used to increase

the signal by 3 dB to compensate. With MIXERAB_GAIN or MIXERCD_GAIN = 1, the gain through the DQM

is sqrt(2) or +3 dB, which can cause clipping of the signal if IIN(t) and QIN(t) are simultaneously near full scale

amplitude and should therefore be used with caution.

7.3.16.5 Low Power Coarse Resolution Mixing Modes

In addition to the NCO the DAC38RFxx also has a coarse mixer block capable of shifting the input signal

spectrum by the fixed mixing frequencies ±N x fDAC/8. Using the coarse mixer instead of the full mixers will result

in lower power consumption.

DAC38RF80, DAC38RF83, DAC38RF84

DAC38RF85, DAC38RF90, DAC38RF93

SLASEA3D – DECEMBER 2016 – REVISED DECEMBER 2023

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DAC38RF83IAAV.B Datasheet(PDF) 64 Page - Texas Instruments

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