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FIR1

FIR2

FIR3

FIR4

IOUTB1

IOUTB2

16-Bit

DAC

DA[15:0]

DB[15:0]

y2

B Gain

B

Offset

FIR1

FIR2

FIR3

FIR4

y2

y2

y2

y2

y2

y2

y2

FIR5

x

sin(x)

+

+/−

cos

sin

sin

cos

DEMUX

Serial Interface

DAC5686

SLWS147B – APRIL 2003 – REVISED AUGUST 2004

DETAILED DESCRIPTION (continued)

NCO mixing frequencies are programmed through 32-bit freq (4 registers); 16-bit phase adjustments are

programmed through phase (2 registers). The NCO operates at the DAC update rate; thus, increased amounts

of interpolation allow for higher IFs. More details for the NCO are provided in the NCO section. For mixing to

nco in register config_msb while in single-sideband or quadrature modulation mode.

Figure 23. Data Path in Quadrature Modulation Mode

In quadrature modulation mode, only one output from the complex mixer stage is routed to the B DAC. The

output can be expressed as:

B(t) = I(t)sin(

ω

or

B(t) = I(t)cos(

ω

Single-sideband up-conversion is achieved when I and Q are Hilbert transform pairs. Upper- or lower-sideband

up-conversion is selected by ssb in the config_msb register, which selects the output from the mixer stage that

is routed out.

The offset and gain features for the B DAC, as previously described, are functional in the quadrature mode.

The serial port of the DAC5686 is a flexible serial interface that communicates with industry-standard

microprocessors and microcontrollers. The interface provides read/write access to all registers used to define the

operating modes of the DAC5686. It is compatible with most synchronous transfer formats and can be configured

as a 3- or 4-pin interface by sif4 in register config_msb. In both configurations, SCLK is the serial-interface

input clock and SDENB is the serial-interface enable. For the 3-pin configuration, SDIO is a bidirectional pin for

both data-in and data-out. For the 4-pin configuration, SDIO is data-in only and SDO is data-out only.

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