DAC5687IPZP datasheet(59/79 Pages) TI

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B0046-01

TRF3701

TRF3702

GND

205

Ω

205

Ω

15.4

Ω

15.4

Ω

15.4

Ω

15.4

Ω

GND

205

Ω

205

Ω

5 V

Ω

5 V

Ω

B0046-02

AQM

205

Ω

205

Ω

205

Ω

205

Ω

5 V

66.5

Ω

66.5

Ω

5 V

66.5

Ω

66.5

Ω

0 V

Nonharmonic Clock-Related Spurious Signals

DAC5687

SLWS164E – FEBRUARY 2005 – REVISED SEPTEMBER 2006

Figure 68. DAC5687 Passive Interface to TRF3701/2 Analog Quadrature Modulator

Changing the voltage levels and resistor values enables other common-mode voltages at the analog quadrature

modulator input. For example, the network shown in Figure 69 can produce a 3.3-V common mode for the

TRF3703-33, with a 0.96-VPP single-ended swing (1.56-VPP differential swing).

Figure 69. DAC5687 Passive Interface to TRF3703-33 Analog Quadrature Modulator

In interpolating DACs, imperfect isolation between the digital and DAC clock circuits generates spurious signals

at frequencies related to the DAC clock rate. The digital interpolation filters in these DACs run at subharmonic

frequencies of the output rate clock, where these frequencies are fDAC/2

N, N = 1 – 3. For example, for X2 mode

there is only one interpolation filter running at fDAC/2; for X4 and X4L modes, on the other hand, there are two

interpolation filters running at fDAC/2 and fDAC/4. In X8 mode, there are three interpolation filters running at fDAC/2,

fDAC/4, and fDAC/8. These lower-speed clocks for the interpolation filter mix with the DAC clock circuit and create

spurious images of the wanted signal and second Nyquist-zone image at offsets of fDAC/2

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