CN-0050 Datasheet, PDF (3/3 Pages) Analog Devices – Stable, Closed-Loop Automatic Power Control for RF Applications

Circuit Note
On the underside of the ADL5330 and AD8318 chip scale
packages, there is an exposed compressed paddle. This paddle is
internally connected to the chip’s ground. Solder the paddle to
the low impedance ground plane on the printed circuit board to
ensure specified electrical performance and to provide thermal
relief. It is also recommended that the ground planes on all
layers under the paddle be stitched together with vias to reduce
thermal impedance.
COMMON VARIATIONS
This circuit can be used to implement a constant power out
function (fixed setpoint with variable input power) or a variable
power out function (variable setpoint with fixed or variable
input power). If a lower output power control range is desired,
the AD8318 log amp (60 dB power detection range) can be
replaced with either the AD8317 (50 dB power detection range)
or the AD8319 (45 dB power detection range). For a constant
output power function, the lowest dynamic range detector
(AD8319) is adequate because the loop always servos the
detector input power to a constant level.
The ADL5330 VGA, which is optimized for transmit applications,
can be replaced by the AD8368 VGA. The AD8368 is optimized
for receive application low frequencies of up to 800 MHz and
provides 34 dB of linear-in-dB voltage-controlled variable gain.
There are a number of DACs suitable for this application. All of
the following DACs have internal references:
Single: AD5660/AD5640/AD5620 (16-bit/14-bit/12-bit),
Dual: AD5663R/AD5643R/AD5623R (16-bit/14-bit/12-bit)
Quad: AD5664R/AD5644R/AD5624R (16-bit/14-bit/12-bit)
CN-0050
LEARN MORE
Dana Whitlow, Design and Operation of Automatic Gain Control
Loops for Receivers in Modern Communications Systems, Analog
Devices Wireless Seminar, Chapter 7, 2006.
MT-031 Tutorial, Grounding Data Converters and Solving the
Mystery of “AGND” and “DGND,” Analog Devices.
MT-073 Tutorial, High Speed Variable Gain Amplifiers, Analog
Devices.
MT-077 Tutorial, Log Amp Basics, Analog Devices.
MT-078 Tutorial, High Speed Log Amps, Analog Devices.
MT-101 Tutorial, Decoupling Techniques, Analog Devices.
Data Sheets
ADL5330
AD8318
AD8317
AD8319
ADL5330 Evaluation Board
AD8318 Evaluation Board
REVISION HISTORY
9/10—Rev. A to Rev. B
Changes to Figure 1 .......................................................................... 1
Changes to Circuit Description Section......................................... 1
Changes to Common Variations Section.......................................3
11/09—Rev. 0 to Rev. A
Updated Format ................................................................. Universal
Changes to Circuit Note Title..........................................................1
10/08—Revision 0: Initial Release
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