max5890 Maxim Integrated Products, Inc., max5890 Datasheet - Page 11

• Manufacturer Part Number: max5890
• Description: Max5890 14-bit, 600msps, High-dynamic-performance Dac With Lvds Inputs
• Manufacturer: Maxim Integrated Products, Inc.

To achieve the best possible jitter performance, the
MAX5890 features flexible differential clock inputs
(CLKP, CLKN) that operate from a separate clock
power supply (AV
the DAC’s phase noise and wideband noise. To
achieve the best DAC dynamic performance, the
CLKP/CLKN input source must be designed carefully.
The differential clock (CLKN and CLKP) input can be
driven from a single-ended or a differential clock
source. Use differential clock drive to achieve the best
dynamic performance from the DAC. For single-ended
operation, drive CLKP with a low noise source and
bypass CLKN to CGND with a 0.1µF capacitor.
Figure 4 shows a convenient and quick way of applying
a differential signal created from a single-ended source
using a wideband transformer. Alternatively, drive
CLKP/CLKN from a CMOS-compatible clock source.
Use sinewave or AC-coupled differential ECL/PECL
drive for best dynamic performance.
Figure 4. Differential Clock-Signal Generation
Figure 5. Differential-to-Single-Ended Conversion Using a Wideband RF Transformer
CLOCK SOURCE
SINGLE-ENDED
14-Bit, 600Msps, High-Dynamic-Performance
PERFORMS SINGLE-ENDED-TO-
WIDEBAND RF TRANSFORMER
DATA INPUTS
DIFFERENTIAL CONVERSION
D0–D13
LVDS
1:1
Applications Information
CLK
______________________________________________________________________________________
). Use a low-jitter clock to reduce
AGND
MAX5890
AGND
25Ω
25Ω
Clock Interface
0.1µF
0.1µF
OUTP
OUTN
TO DAC
CLKP
CLKN
50Ω
100Ω
50Ω
Use a pair of transformers (Figure 5) or a differential
amplifier configuration to convert the differential voltage
existing between OUTP and OUTN to a single-ended
voltage. Optimize the dynamic performance by using a
differential transformer-coupled output and limit the out-
put power to < 0dBm full scale. To achieve the best
dynamic performance, use the differential transformer
configuration. Terminate the DAC as shown in Figure 5,
and use 50Ω termination at the transformer single-
ended output. This will provide double 50Ω termination
for the DAC output network. With the double-terminated
output and 20mA full-scale current, the DAC will pro-
duce a full-scale signal level of approximately -2dBm.
Pay close attention to the transformer core saturation
characteristics when selecting a transformer for the
MAX5890. Transformer core saturation can introduce
strong 2nd-order harmonic distortion especially at low
output frequencies and high signal amplitudes. For best
results, connect the center tap of the transformer to
ground. When not using a transformer, terminate each
DAC output to ground with a 25Ω resistor. Additionally,
place a 50Ω resistor between the outputs (Figure 6).
For a single-ended unipolar output, select OUTP as the
output and connect OUTN to AGND. Operating the
MAX5890 single-ended is not recommended because
it degrades the dynamic performance.
The distortion performance of the DAC depends on the
load impedance. The MAX5890 is optimized for 50Ω
differential double termination. Using higher termination
impedance degrades distortion performance and
increases output noise voltage.
T1, 1:1
DAC with LVDS Inputs
Differential Output Coupling Using a
WIDEBAND RF TRANSFORMER T2 PERFORMS THE
DIFFERENTIAL-TO-SINGLE-ENDED CONVERSION
T2, 1:1
Wideband RF Transformer
V
OUT
, SINGLE-ENDED
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