50 Hz to 2.7 GHz
60 dB TruPwr™ Detector
AD8362
FEATURES
FUNCTIONAL BLOCK DIAGRAM
DECL
CHPF
Complete fully calibrated measurement/control system
Accurate rms-to-dc conversion from 50 Hz to 2.7 GHz
Input dynamic range of >60 dB: −52 dBm to +8 dBm in 50 Ω
Waveform and modulation independent:
(Such as GSM/CDMA/TDMA)
INHI
2
x
CLPF
VOUT
ACOM
INLO
Linear-in-decibels output, scaled 50 mV/dB
Law conformance error of 0.5 dB
All functions temperature and supply stable
Operates from 4.5 V to 5.5 V at 24 mA from −40°C to +85°C
Power-down capability to 1.3 mW
2
V
TGT
x
VSET
VPOS
AD8362
APPLICATIONS
Power amplifier linearization/control loops
BIAS
VREF
Transmitter power control
Transmitter signal strength indication (TSSI)
RF instrumentation
COMM
PWDN
Figure 1.
GENERAL DESCRIPTION
The AD8362 is a true rms-responding power detector that has a
60 dB measurement range. It is intended for use in a variety of
high frequency communication systems and in instrumentation
requiring an accurate response to signal power. It is easy to use,
requiring only a single supply of 5 V and a few capacitors. It can
operate from arbitrarily low frequencies to over 2.7 GHz and
can accept inputs that have rms values from 1 mV to at least
1 V rms, with peak crest factors of up to 6, exceeding the
requirements for accurate measurement of CDMA signals.
the input power. Optionally, the voltage at VSET may be a
replica of the RF signal’s amplitude modulation, in which case
the overall effect is to remove the modulation component prior
to detection and low-pass filtering. The corner frequency of the
averaging filter may be lowered without limit by adding an
external capacitor at the CLPF pin. The AD8362 can be used to
determine the true power of a high frequency signal having a
complex low frequency modulation envelope (or simply as a
low frequency rms voltmeter). The high-pass corner generated
by its offset-nulling loop can be lowered by a capacitor added
on the CHPF pin.
The input signal is applied to a resistive ladder attenuator
that comprises the input stage of a variable gain amplifier.
The 12 tap points are smoothly interpolated using a proprietary
technique to provide a continuously variable attenuator, which
is controlled by a voltage applied to the VSET pin. The resulting
signal is applied to a high performance broadband amplifier. Its
output is measured by an accurate square-law detector cell. The
fluctuating output is then filtered and compared with the output
of an identical squarer, whose input is a fixed dc voltage applied
to the VTGT pin, usually the accurate reference of 1.25 V
provided at the VREF pin.
Used as a power measurement device, VOUT is strapped to
VSET, and the output is then proportional to the logarithm of
the rms value of the input; that is, the reading is presented
directly in decibels and is conveniently scaled 1 V per decade,
that is, 50 mV/dB; other slopes are easily arranged. In controller
modes, the voltage applied to VSET determines the power level
required at the input to null the deviation from the setpoint.
The output buffer can provide high load currents.
The AD8362 is powered down by a logic high applied to the
PWDN pin, i.e., the consumption is reduced to about 1.3 mW. It
powers up within about 20 µs to its nominal operating current
of 20 mA at 25°C. The AD8362 is supplied in a 16-lead TSSOP
package for operation over the industrial temperature range of
−40°C to +85°C. An evaluation board is available.
The difference in the outputs of these squaring cells is
integrated in a high gain error amplifier, generating a voltage at
the VOUT pin with rail-to-rail capabilities. In a controller
mode, this low noise output can be used to vary the gain of a
host system’s RF amplifier, thus balancing the set point against
Rev. B
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.326.8703
www.analog.com
© 2004 Analog Devices, Inc. All rights reserved.
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