MAX5874 Maxim Integrated Products, MAX5874 Datasheet - Page 13

• Manufacturer Part Number: MAX5874
• Description: Dual DAC with LVDS Inputs
• Manufacturer: Maxim Integrated Products

Use a pair of transformers (Figure 6) or a differential
amplifier configuration to convert the differential voltage
existing between OUTIP/OUTQP and OUTIN/OUTQN to
a single-ended voltage. Optimize the dynamic perfor-
mance by using a differential transformer-coupled output
to limit the output power to <0dBm full scale. Pay close
attention to the transformer core saturation characteris-
tics when selecting a transformer for the MAX5874.
Transformer core saturation can introduce strong 2nd-
order harmonic distortion, especially at low output fre-
quencies and high signal amplitudes. For best results,
center tap 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 7).
Figure 5. Differential Clock-Signal Generation
Figure 6. Differential-to-Single-Ended Conversion Using a Wideband RF Transformer
CLOCK SOURCE
(e.g., HP 8662A)
SINGLE-ENDED
Differential-to-Single-Ended Conversion
14-Bit, 200Msps, High-Dynamic-Performance,
PERFORMS SINGLE-ENDED-TO-
WIDEBAND RF TRANSFORMER
DIFFERENTIAL CONVERSION
DATA13–DATA0
Using a Wideband RF Transformer
1:1
14
______________________________________________________________________________________
GND
MAX5874
GND
25Ω
25Ω
0.1µF
0.1µF
OUTIP/OUTQP
OUTIN/OUTQN
TO DAC
CLKP
CLKN
Dual DAC with CMOS Inputs
50Ω
100Ω
50Ω
For a single-ended unipolar output, select OUTIP
(OUTQP) as the output and ground OUTIN (OUTQN) to
GND. Driving the MAX5874 single-ended is not recom-
mended since additional noise and distortion will
be added.
The distortion performance of the DAC depends on the
load impedance. The MAX5874 is optimized for 50Ω
differential double termination. It can be used with a
transformer output as shown in Figure 6 or just one 25Ω
resistor from each output to ground and one 50Ω resis-
tor between the outputs (Figure 7). This produces a full-
scale output power of up to -2dBm, depending on the
output current setting. Higher termination impedance
can be used at the cost of degraded distortion perfor-
mance and increased output noise voltage.
Grounding and power-supply decoupling can strongly
influence the MAX5874 performance. Unwanted digital
crosstalk couples through the input, reference, power
supply, and ground connections, and affects dynamic
performance. High-speed, high-frequency applications
require closely followed proper grounding and power-
supply decoupling. These techniques reduce EMI and
internal crosstalk that can significantly affect the
MAX5874 dynamic performance.
Use a multilayer printed circuit (PC) board with sepa-
rate ground and power-supply planes. Run high-speed
signals on lines directly above the ground plane. Keep
digital signals as far away from sensitive analog inputs
and outputs, reference input sense lines, and clock
inputs as practical. Use a controlled-impedance sym-
metric design of clock input and the analog output lines
to minimize 2nd-order harmonic distortion components,
T1, 1:1
Grounding, Bypassing, and Power-
WIDEBAND RF TRANSFORMER T2 PERFORMS THE
DIFFERENTIAL-TO-SINGLE-ENDED CONVERSION
T2, 1:1
V
OUT
, SINGLE-ENDED
Supply Considerations
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