DAC5682Z datasheet(49/59 Pages) TI

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DUAL CHANNEL REAL IF OUTPUT RADIO

DAC-A

DAC-B

100

opt.

PLL

Loop

Filter

DLL

DAC5682ZDAC

FPGA

PLL

÷1

÷4

ClockDivider /

Distribution

CDCM7005

100

250 MHz

1000 MHz

PLL/

DLL

VCO

N-

Divider

R-

Div

PFD

CPOUT

VCTRL_IN

TRF3761-XPLL/VCO

Loop

Filter

Div

1/2/4

DCLKP/N

SYNCP/N

D0P/N

D15P/N

375 MHzMinto 2380 MHzMax

(Dependsondividerand

“dash #” ofTRF3761)

10 MHz

OSC

Note : Forclarity, onlysignalpathsareshown.

Loop

Filter

VCXO

3.3V

Processing

Interleaved

A/BData

DIRECT CONVERSION RADIO

DAC5682Z

www.ti.com ........................................................................................................................................................ SLLS853C – AUGUST 2007 – REVISED JUNE 2009

APPLICATIONS EXAMPLES (continued)

Refer to Figure 50 for an example Dual Channel Real IF Output Radio. The DAC5682Z receives an interleaved

A/B input data stream and increases the sample rate through interpolation by a factor of 2 or 4. By performing

digital interpolation on the input data, undesired images of the original signal can be push out of the band of

interest and more easily suppressed with analog filters. Real mixing is available at each stage of interpolation

using the CMIX0 and CMIX1 blocks to up-convert the signal. (See Dual-Channel Real Upconversion section)

Both DAC output signals would typically be terminated with a transformer (see the Analog Current Output

section). An IF filter, either LC or SAW, is used to suppress the DAC Nyquist zone images and other spurious

signals before being mixed to RF with a mixer. The TRF3671 Frequency Synthesizer, with integrated VCO, may

be used to drive a common LO input of the mixers for frequencies between 375 and 2380 MHz. Alternatively, two

separate TRF3761 synthesizers could be used for independent final RF frequency placement.

Figure 50. System Diagram of a Dual Channel Real IF Output Radio

Refer to Figure 51 for an example Direct Conversion Radio. The DAC5682Z receives an interleaved complex I/Q

baseband input data stream and increases the sample rate through interpolation by a factor of 2 or 4. By

performing digital interpolation on the input data, undesired images of the original signal can be push out of the

band of interest and more easily suppressed with analog filters.

For a Zero IF (ZIF) frequency plan, complex mixing of the baseband signal is not required. Alternatively, for a

Complex IF frequency plan the input data can be placed at an pre-placed at an IF within the bandwidth

limitations of the interpolation filters. In addition, complex mixing is available at each stage of interpolation using

the CMIX0 and CMIX1 blocks to up-convert the signal to a frequency placement at a multiples ±Fdac/8 or

±Fdac/4. The output of both DAC channels is used to produce a Hilbert transform pair and can be expressed as:

A(t) = I(t)cos(

ct) – Q(t)sin(ωct) m(t)

(3)

A(t) = I(t)cos(

ct) – Q(t)sin(ωct) mh(t)

(4)

where m(t) and mh(t) connote a Hilbert transform pair and

ωc is the sum of the CMIX0 and CMIX1 frequencies.

The complex output is input to an analog quadrature modulator (AQM) such as the Texas Instruments

TRF3703-33 for a single side-band (SSB) up conversion to RF. A passive (resistor only) interface to the AQM is

recommended, with an optional LC filter network. The TRF3671 Frequency Synthesizer with integrated VCO may

be used to drive the LO input of the TRF3703-33 for frequencies between 375 and 2380 MHz. Upper

single-sideband upconversion is achieved at the output of the analog quadrature modulator, whose output is

expressed as:

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