fO − Output Frequency − MHz

−70

−60

−50

−40

−30

−20

−10

0

0

25

50

75

100

125

150

175

G020

IF − fDAC/2

IF

± fDAC/8

IF − fDAC y 3/4

IF

± fDAC/4

fO − Output Frequency − MHz

−70

−60

−50

−40

−30

−20

−10

0

0

25

50

75

100

125

150

175

G021

IF − fDAC/2

IF

± fDAC/8

IF − fDAC y 3/4

IF

± fDAC/4

DAC5686

www.ti.com ............................................................................................................................................................ SLWS147F – APRIL 2003 – REVISED JUNE 2009

(a)

(b)

Figure 29. Typical Amplitude of Clock-Related Spurious Signals in (a) External-Clock Mode and (b) PLL

Mode

The amplitudes in Figure 29 are typical values and will vary by a few dB across different parts, supply voltages,

and temperatures. Figure 28 and Figure 29 can be used to estimate the non-harmonic clock-related harmonic

signals. Take the example for using the DAC5686 in external-clock mode, fDAC = 500 MHz, 4× interpolation, and

IF = 85 MHz with a real output. Figure 28(b) and Figure 29(a) predict the spurious signals shown in Table 4.

Table 4. Predicted Frequency and Amplitude for

fDAC – 500 MHz, 4× Interpolation, IF = 85 MHz in

External-Clock Mode

Spurious Signal

Frequency (MHz)

Amplitude (dBc)

IF – fDAC/2

165

–47

IF + fDAC/4

210

–64

IF – fDAC/4

40

–64

IF – fDAC × 3/4

> 250

N/A

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