Datasheet

AD9737A/AD9739A Data Sheet
Rev. | Page 56 of 64
CLOCK INPUT CONSIDERATIONS
D
D
Q
V
CC
V
EE
V
T
Q
V
REF
50Ω 50Ω
50Ω
50Ω
50Ω
DACCLK_P
DACCLK_N
100Ω
10nF
10nF
ADCLK914
AD9737A/AD9739A
10nF
10nF
50Ω
09616-092
Figure 173. ADCLK914 Interface to the AD9737A/AD9739A CLK Input
VCO
PLL
ADF4350
FREF
1.8V p-p
V
VCO
1nF
1nF
3.9nH
RF
OUT
A–
RF
OUT
A+
RF
OUT
A–
RF
OUT
A+
100Ω
DACCLK_P
DACCLK_N
DIV-BY-2
N
N = 0 – 4
09616-093
AD9737A/AD9739A
Figure 174. ADF4350 Interface to the AD9737A/AD9739A CLK Input
The quality of the clock source and its drive strength are important
considerations in maintaining the specified ac performance.
The phase noise and spur characteristics of the clock source
should be selected to meet the target application requirements.
Phase noise and spurs at a given frequency offset on the clock
source are directly translated to the output signal. It can be shown
that the phase noise characteristics of a reconstructed output
sine wave are related to the clock source by 20 × log10(f
OUT
/f
CLK
)
when the DAC clock path contribution, along with thermal and
quantization effects, are negligible.
The AD9737A/AD9739A clock receiver provides optimum jitter
performance when driven by a fast slew rate originating from
the LVPECL or CML output drivers. For a low jitter sinusoidal
clock source, the ADCLK914 can be used to square-up the signal
and provide a CML input signal for the AD9737A/AD9739A
clock receiver. Note that all specifications and characterization
presented in the data sheet are with the ADCLK914 driven by a
high quality RF signal generator with the clock receiver biased at
an 800 mV level.
Figure 174 shows a clock source based on the ADF4350 low phase
noise/jitter PLL. The ADF4350 can provide output frequencies
from 140 MHz up to 4.4 GHz with jitter as low as 0.5 ps rms.
Each single-ended output can provide a squared-up output
level that can be varied from −4 dBm to +5 dBm, allowing for
>2 V p-p output differential swings. The ADF4350 also includes
an additional CML buffer that can be used to drive another
AD9737A/AD9739A device.
ESD
DACCLK_P
DACCLK_N
VDDC
VSSC
CLKx_OFFSET
DIR_x = 0
CLKx_OFFSET
DIR_x =
0
4-BIT PMOS
IOUT ARRAY
4-BIT NMOS
IOUT ARRAY
09616-094
Figure 175. Clock Input and Common-Mode Control
C