DAC5686IPZP datasheet(17/46 Pages) TI

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IOUTA1

IOUTA2

16-Bit

DAC

DA[15:0]

DB[15:0]

2 – 16 y Fdata

Fdata

y2 – y16

A Gain

Offset

FIR5

sin(x)

cos

sin

y2 – y16

+/−

IOUTB1

IOUTB2

16-Bit

DAC

B Gain

Offset

sin(x)

sin

cos

DEMUX

DAC5686

SLWS147B – APRIL 2003 – REVISED AUGUST 2004

DETAILED DESCRIPTION (continued)

Figure 19. Data Path in SSB Mode

Figure 20 shows the DAC5686 interfaced to an RF quadrature modulator. The outputs of the complex mixer

stage can be expressed as:

A(t) = I(t)cos(

ct) – Q(t)sin(ωct) = m(t)

B(t) = I(t)sin(

ct) + Q(t)cos(ωct) = mh(t)

where m(t) and mh(t) connote a Hilbert transform pair. Upper single-sideband up-conversion is achieved at the

output of the analog quadrature modulator, whose output is expressed as:

IF(t) = A(t)cos(

c+ ω1)t – B(t)sin(ωc+ ω1)t

Flexibility is provided to the user by allowing for the selection of –B(t) out, which results in lower-sideband

up-conversion. This option is selected by ssb in the config_msb register. Figure 21 depicts the magnitude

spectrum along the signal path during single-sideband up-conversion for real input. Further flexibility is provided

to the user by allowing for the inverse of sin to be used in the complex mixer by programming rspect in the

config_usb register. The four combinations of rspect and ssb allow the user to select one of four complex

spectral bands to input to a quadrature modulator (see Figure 22).

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