MAX5876 Maxim Integrated Products, MAX5876 Datasheet - Page 15

• Manufacturer Part Number: MAX5876
• Description: Dual DAC with LVDS Inputs
• Manufacturer: Maxim Integrated Products

Use a pair of transformers (Figure 7) 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 out-
put and limit the output power to <0dBm full scale. Pay
close attention to the transformer core saturation char-
acteristics when selecting a transformer for the
MAX5876. Transformer core saturation can introduce
strong 2nd-order harmonic distortion especially at low
output frequencies 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 8).
For a single-ended unipolar output, select OUTIP
(OUTQP) as the output and ground OUTIN (OUTQN).
Driving the MAX5876 single-ended is not recommended
since additional noise and distortion will be added.
The distortion performance of the DAC depends on the
load impedance. The MAX5876 is optimized for 50Ω
differential double termination. It can be used with a
transformer output as shown in Figure 7 or just one 25Ω
resistor from each output to ground and one 50Ω resis-
tor between the outputs (Figure 8). 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.
Figure 7. Differential-to-Single-Ended Conversion Using a Wideband RF Transformer
Differential-to-Single-Ended Conversion
12-Bit, 250Msps, High-Dynamic-Performance,
DATA11–DATA0
Using a Wideband RF Transformer
12
______________________________________________________________________________________
MAX5876
GND
OUTIP/OUTQP
OUTIN/OUTQN
Dual DAC with LVDS Inputs
50Ω
100Ω
50Ω
Grounding and power-supply decoupling can strongly
influence the MAX5876 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
MAX5876 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, differential design of clock input and the analog
output lines to minimize 2nd-order harmonic distortion
components, thus optimizing the DAC’s dynamic per-
formance. Keep digital signal paths short and run
lengths matched to avoid propagation delay and data
skew mismatches.
The MAX5876 requires five separate power-supply inputs
for analog (AV
DV
pins must be connected to their proper supply. Decouple
each AV
0.1µF capacitor as close to the device as possible with
the shortest possible connection to the ground plane
(Figure 9). Minimize the analog and digital load capaci-
tances for optimized operation. Decouple all three power-
supply voltages at the point they enter the PC board with
T1, 1:1
DD3.3
), and clock (AV
DD
, DV
Grounding, Bypassing, and Power-
DD1.8
DD
WIDEBAND RF TRANSFORMER T2 PERFORMS THE
DIFFERENTIAL-TO-SINGLE-ENDED CONVERSION
T2, 1:1
, and AV
and AV
V
CLK
OUT
Supply Considerations
CLK
, SINGLE-ENDED
DD3.3
) circuitry. All power-supply
input pin with a separate
), digital (DV
www.DataSheet4U.com
DD1.8
and
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