CN-0178 Datasheet, PDF (1/5 Pages) Analog Devices – Software-Calibrated, 50 MHz to 9 GHz, RF Power Measurement System

Circuit Note
CN-0178
Circuits from the Lab™ reference circuits are engineered and
tested for quick and easy system integration to help solve today’s
analog, mixed-signal, and RF design challenges. For more
information and/or support, visit www.analog.com/CN0178.
Devices Connected/Referenced
ADL5902 50 MHz to 9 GHz, 65 dB TruPwr™ Detector
AD7466 Micropower, 12-Bit, 200 kSPS SAR ADC
Software-Calibrated, 50 MHz to 9 GHz, RF Power Measurement System
EVALUATION AND DESIGN SUPPORT
Circuit Evaluation Boards
CN-0178 Circuit Evaluation Board (EVAL-CN0178-SDPZ)
System Demonstration Platform (EVAL-SDP-CB1Z)
Design and Integration Files
Schematics, Layout Files, Bill of Materials
CIRCUIT FUNCTION AND BENEFITS
This circuit uses the ADL5902 TruPwr™ detector to measure the
rms signal strength of RF signals with varying crest factors
(peak-to-average ratio) over a dynamic range of approximately
65 dB and operates at frequencies from 50 MHz up to 9 GHz.
+5V
C3
0.1µF
+5V
C7
0.1µF
C4
100pF
C5
100pF
The measurement result is provided as serial data at the output
of a 12-bit ADC (AD7466). A simple 4-point system calibration
at ambient temperature is performed in the digital domain.
The interface between the RF detector and the ADC is
straightforward, consisting of two signal scaling resistors and
no active components. In addition, the ADL5902 internal 2.3 V
reference voltage provides the supply and reference voltage for
the micropower ADC. The AD7466 has no pipeline delay and
is operated as a read-only SAR ADC.
The overall circuit achieves temperature stability of
approximately ±0.5 dB.
VPOS
3
VPOS
10
ADL5902
TEMPERATURE
SENSOR
8 TEMP
RFIN
R3
60.4Ω
C10
100pF
INHI
14
INLO
15
C12
100pF
LINEAR-IN-dB VGA
(NEGATIVE SLOPE)
NC 2
I_DET
X²
X²
I_TGT
VSET
7
V_IN
R10
1.21kΩ
3 T/H
G=5
6
R11
VOUT
2kΩ
NC 16
NC 13
BIAS AND POWER-
DOWN CONTROL
VREF
2.3V
26pF
CLPF
5
C9
0.1µF
1
11
12
9
4
TADJ
VREF
VTGT
COMM COMM
R12
301Ω
R9
1430Ω
R10
3.74kΩ
R11
2kΩ
C9A
0.1µF
V_DD
1
C10A
10µF
12-BIT
SUCCESSIVE
APPROXIMATION
ADC
CONTROL
LOGIC
AD7466
2
GND
SCLK
4
SDATA
5
CS
6
CLK
DATA
CS
DGND
Figure 1. Software-Calibrated RF Power Measurement System
Rev.A
Circuits from the Lab™ circuits from Analog Devices have been designed and built by Analog Devices
engineers. Standard engineering practices have been employed in the design and construction of
each circuit, and their function and performance have been tested and verified in a lab environment at
room temperature. However, you are solely responsible for testing the circuit and determining its
suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices
be liable for direct, indirect, special, incidental, consequential or punitive damages due to any cause
whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page)
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone]
www.analog.com
Fax: [phone] ©2010–2011 Analog Devices, Inc. All rights reserved.