AD9857AST Analog Devices Inc, AD9857AST Datasheet - Page 35

• Manufacturer Part Number: AD9857AST
• Description: IC QUADRATURE DGTL UPCONV 80LQFP
• Manufacturer: Analog Devices Inc
• Series: AD9857r

Specifications of AD9857AST

• Rohs Status: RoHS non-compliant
• Function: Upconverter
• Frequency: 5MHz ~ 200MHz
• Rf Type: HFC Cable Network
• Package / Case: 80-LQFP

Supply Voltage
This affects power dissipation and junction temperature
because power dissipation equals supply voltage multiplied by
supply current. It is recommended that the user design for a
3.3 V nominal supply voltage in order to manage the effect of
supply voltage on the junction temperature of the AD9857.
Clock Speed
This directly and linearly influences the total power dissipation
of the device and, therefore, junction temperature. As a rule, the
user should always select the lowest internal clock speed
possible to support a given application to minimize power
dissipation. Typically, the usable frequency output bandwidth
from a DDS is limited to 40% of the system clock rate to keep
reasonable requirements on the output low-pass filter. This
means that for the typical DDS application, the system clock
frequency should be 2.5 times the highest output frequency.
Operating Modes
The AD9857 has three operating modes that consume
significantly different amounts of power. When operating in
the quadrature modulation mode, the AD9857 dissipates about
twice the power as when operating as a single-tone DDS. When
operating as a quadrature modulator, the AD9857 has features
that facilitate power management tactics. For example, the
TxENABLE pin may be used in conjunction with the auto
power-down bit to frame bursts of data and automatically
switch the device into a low power state when there is no data to
be modulated.
Rev. C| Page 35 of 40
Equivalent I/O Circuits
SUPPORT
Applications assistance is available for the AD9857 and the
AD9857/PCB evaluation board. Please call 1-800-ANALOGD
or visit www.analog.com/dds.
DAC OUTPUTS
IOUT IOUTB
V
DD
Figure 35. Equivalent I/O Circuits
V
DD
DIGITAL
OUT
DIGITAL
IN
AD9857
V
DD