DAC5687MPZPEP datasheet(58/75 Pages) TI1

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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

Non-Harmonic Clock-Related Spurious Signals

DAC5687-EP

SGLS333 – JUNE 2006

Figure 66. DAC5687 Passive Interface to TRF3701/2 Analog Quadrature Modulator

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

modulator input. For example, the network shown in Figure 67 can produce a 1.5-V common mode at the analog

quadrature modulator input, with a 0.78-VPP single-ended swing (1.56-VPP differential swing), or 0.2-dB insertion

loss.

Figure 67. DAC5687 Passive Interface With 1.5-V Common Mode at AQM Input

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

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

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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