Datasheet

f
O
− Output Frequency − MHz
−70
−60
−50
−40
−30
−20
−10
0
0 25 50 75 100 125 150 175
Amplitude − dBc
G020
IF − f
DAC
/2
IF ± f
DAC
/8
IF − f
DAC
y 3/4
IF ± f
DAC
/4
f
O
− Output Frequency − MHz
−70
−60
−50
−40
−30
−20
−10
0
0 25 50 75 100 125 150 175
Amplitude − dBc
G021
IF − f
DAC
/2
IF ± f
DAC
/8
IF − f
DAC
y 3/4
IF ± f
DAC
/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, f
DAC
= 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
f
DAC
– 500 MHz, 4 × Interpolation, IF = 85 MHz in
External-Clock Mode
Spurious Signal Frequency (MHz) Amplitude (dBc)
IF – f
DAC
/2 165 – 47
IF + f
DAC
/4 210 – 64
IF – f
DAC
/4 40 – 64
IF – f
DAC
× 3/4 > 250 N/A
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