CN-0150 Datasheet, PDF (1/5 Pages) Analog Devices – Software-Calibrated, 1 MHz to 8 GHz, 60 dB RF Power Measurement System Using a Logarithmic Detector

Circuit Note
CN-0150
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/CN0150.
Devices Connected/Referenced
AD8318
1 MHz to 8 GHz, 70 dB, Logarithmic
Detector/Controller
AD7887
2.7 V to 5.25 V, Micropower, 2-Channel,
125 kSPS, 12-Bit ADC in 8-Lead MSOP
ADR421 Precision, Low Noise, 2.5 V Reference
Software-Calibrated, 1 MHz to 8 GHz, 60 dB RF Power
Measurement System Using a Logarithmic Detector
EVALUATION AND DESIGN SUPPORT
Circuit Evaluation Boards
CN-0150 Circuit Evaluation Board (EVAL-CN0150A-SDPZ)
System Demonstration Platform (EVAL-SDP-CB1Z)
Design and Integration Files
Schematics, Layout Files, Bill of Materials
CIRCUIT FUNCTION AND BENEFITS
This circuit measures RF power at any frequency from
1 MHz to 8 GHz over a range of approximately 60 dB. The
measurement result is provided as a digital code at the output of
a 12-bit ADC with serial interface and integrated reference. The
output of the RF detector has a glueless interface to the ADC and
uses most of the ADC’s input range without further adjustment.
A simple two-point system calibration is performed in the
digital domain.
The AD8318 maintains accurate log conformance for signals of
1 MHz to 6 GHz and provides useful operation to 8 GHz.
The device provides a typical output voltage temperature
stability of ±0.5 dB.
The AD7887 ADC can be configured for either dual or single
channel operation via the on-chip control register. There is a
default single-channel mode that allows the AD7887 to be operated
as a read-only ADC, thereby simplifying the control logic.
Typical data is shown for the two devices operating over a
−40°C to +85°C temperature range.
PULSED RF
INPUT
R_FIN
+5V
V_POS
R1
52.3Ω
R4
499Ω
C1 1nF
C2 1nF
12
11
10
9
CMIP CMIP TADJ VPSO
13 TEMP
CMOP 8
14 INHI
15 INLO
VSET 7
AD8318
VOUT 6
16 ENBL
CLPF 5
CMIP CMIP VPSI VPSI
1
2
3
4
C5
0.1µF
10µF
0.1µF
C6
100pF
V_OUT
SEE
TEXT
0.1µF
V_DD
AD7887
AIN0
SCLK
SERIAL
INTERFACE
AIN1/
V_REF
DOUT
DIN
C9
0.1µF
GND
CS
C7
100pF
V_POS
C8
0.1µF
Figure 1. Software-Calibrated RF Measurement System (Simplified Schematic: All Connections Not Shown)
µC/µP
Rev. C
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