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a
AD8302
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329–4700 www.analog.com
Fax: 781/326-8703 © Analog Devices, Inc., 2001
LF–2.7 GHz
RF/IF Gain and Phase Detector
FUNCTIONAL BLOCK DIAGRAM
MFLT
VMAG
MSET
PSET
VPHS
PFLT
VREF
VIDEO OUTPUT – A
INPA
OFSA
COMM
OFSB
INPB
VPOS
+
–
+
–
60dB LOG AMPS
(7 DETECTORS)
60dB LOG AMPS
(7 DETECTORS)
VIDEO OUTPUT – B
PHASE
DETECTOR
+
–
BIAS
x3
1.8V
AD8302
FEATURES
Measures Gain/Loss and Phase up to 2.7 GHz
Dual Demodulating Log Amps and Phase Detector
Input Range –60 dBm to 0 dBm in a 50 ⍀ System
Accurate Gain Measurement Scaling (30 mV/dB)
Typical Nonlinearity < 0.5 dB
Accurate Phase Measurement Scaling (10 mV/Degree)
Typical Nonlinearity < 1 Degree
Measurement/Controller/Level Comparator Modes
Operates from Supply Voltages of 2.7 V–5.5 V
Stable 1.8 V Reference Voltage Output
Small Signal Envelope Bandwidth from DC to 30 MHz
APPLICATIONS
RF/IF PA Linearization
Precise RF Power Control
Remote System Monitoring and Diagnostics
Return Loss/VSWR Measurements
Log Ratio Function for AC Signals
PRODUCT DESCRIPTION
The AD8302 is an innovative, fully integrated system for mea-
suring gain/loss and phase in numerous receive, transmit, and
instrumentation applications. It requires few external compo-
nents and a single supply of 2.7 V–5.5 V. The ac-coupled input
signals can range from –60 dBm to 0 dBm in a 50 Ω system, from
low frequencies up to 2.7 GHz. The outputs provide an accu-
rate measurement of either gain or loss over a ±30 dB range
scaled to 30 mV/dB, and of phase over a 0°–180° range scaled to
10 mV/degree. Both subsystems have an output bandwidth of
30 MHz, which may optionally be reduced by the addition of
external filter capacitors. The AD8302 can be used in direct
control mode to servo gain and phase of a signal chain toward
predetermined setpoints.
The AD8302 comprises a closely matched pair of demodulating
logarithmic amplifiers, each having a 60 dB measurement range.
By taking the difference of their outputs, a measurement of
the magnitude ratio or gain between the two input signals is
available. These signals may even be at different frequencies,
allowing the measurement of conversion gain or loss. The AD8302
may be used to determine absolute signal level by applying the
unknown signal to one input and a calibrated ac reference signal
to the other. With the output stage feedback connection dis-
abled, a comparator may be realized, using the setpoint pins
MSET and PSET to program the thresholds.
The signal inputs are single-ended, allowing them to be matched
and connected directly to a directional coupler. Their input
impedance is nominally 3 kΩ at low frequencies.
The AD8302 includes a phase detector of the multiplier type,
but with precise phase balance, driven by the fully limited sig-
nals appearing at the outputs of the two logarithmic amplifiers.
Thus, the phase accuracy measurement is independent of signal
level over a wide range.
The phase and gain output voltages are simultaneously available
at loadable ground referenced outputs over the standard output
range of 0 V to 1.8 V. The output drivers can source or sink up
to 8 mA. A loadable, stable reference voltage of 1.8 V is avail-
able for precise repositioning of the output range by the user.
In controller applications, the connection between the gain
output pin VMAG and the setpoint control pin MSET is broken.
The desired setpoint is presented to MSET and the VMAG
control signal drives an appropriate external variable gain device.
Likewise, the feedback path between the phase output pin VPHS
and its setpoint control pin PSET may be broken, to allow
operation as a phase controller.
The AD8302 is fabricated on Analog Devices’ proprietary, high-
performance 25 GHz SOI complementary bipolar IC process. It is
available in a 14-lead TSSOP package and operates over a –40°C
to +85°C temperature range. An evaluation board is available.
