Fast, Voltage-Out DC–440 MHz,
95 dB Logarithmic Amplifier
AD8310
FEATURES
FUNCTIONAL BLOCK DIAGRAM
Multistage demodulating logarithmic amplifier
Voltage output, rise time <15 ns
AD8310
VPOS
ENBL
BFIN
BAND GAP REFERENCE
AND BIASING
8mA
ENABLE
SUPPLY
5
7
6
High current capacity: 25 mA into grounded RL
95 dB dynamic range: −91 dBV to +4 dBV
Single supply of 2.7 V min at 8 mA typ
DC–440 MHz operation, 0.4 dB linearity
Slope of +24 mV/dB, intercept of −108 dBV
Highly stable scaling over temperature
Fully differential dc-coupled signal path
100 ns power-up time, 1 mA sleep current
SIX 14.3dB 900MHz
AMPLIFIER STAGES
BUFFER
INPUT
INHI
+INPUT
–INPUT
8
1
1.0kΩ
INLO
3
MIRROR
2µA
dB
3kΩ
COMM
+
–
VOUT
4
3
OUTPUT
/
2
3kΩ
NINE DETECTOR CELLS
SPACED 14.3dB
1kΩ
COMM
2
COMMON
COMM
OFLT
33pF
OFFSET
FILTER
INPUT-OFFSET
COMPENSATION LOOP
COMM
APPLICATIONS
Figure 1.
Conversion of signal level to decibel form
Transmitter antenna power measurement
Receiver signal strength indication (RSSI)
Low cost radar and sonar signal processing
Network and spectrum analyzers
The fully differential input offers a moderately high impedance
(1 kΩ in parallel with about 1 pF). A simple network can match
the input to 50 Ω and provide a power sensitivity of −78 dBm to
+17 dBm. The logarithmic linearity is typically within 0.4 dB
up to 100 MHz over the central portion of the range, but it is
somewhat greater at 440 MHz. There is no minimum frequency
limit; the AD8310 can be used down to low audio frequencies.
Special filtering features are provided to support this wide
range.
Signal-level determination down to 20 Hz
True-decibel ac mode for multimeters
GENERAL DESCRIPTION
The AD8310 is a complete, dc–440 MHz demodulating
logarithmic amplifier (log amp) with a very fast voltage mode
output, capable of driving up to 25 mA into a grounded load in
under 15 ns. It uses the progressive compression (successive
detection) technique to provide a dynamic range of up to 95 dB
to 3 dB law conformance or 90 dB to a 1 dB error bound up
to 100 MHz. It is extremely stable and easy to use, requiring no
significant external components. A single-supply voltage of
2.7 V to 5.5 V at 8 mA is needed, corresponding to a power
consumption of only 24 mW at 3 V. A fast-acting CMOS-
compatible enable pin is provided.
The output voltage runs from a noise-limited lower boundary
of 400 mV to an upper limit within 200 mV of the supply
voltage for light loads. The slope and intercept can be readily
altered using external resistors. The output is tolerant of a wide
variety of load conditions and is stable with capacitive loads of
100 pF.
The AD8310 provides a unique combination of low cost, small
size, low power consumption, high accuracy and stability, high
dynamic range, a frequency range encompassing audio to UHF,
fast response time, and good load-driving capabilities, making
this product useful in numerous applications that require the
reduction of a signal to its decibel equivalent.
Each of the six cascaded amplifier/limiter cells has a small-
signal gain of 14.3 dB, with a −3 dB bandwidth of 900 MHz.
A total of nine detector cells are used to provide a dynamic
range that extends from −91 dBV (where 0 dBV is defined as
the amplitude of a 1 V rms sine wave), an amplitude of about
40 ꢀV, up to +4 dBV (or 2.2 V). The demodulated output
is accurately scaled, with a log slope of 24 mV/dB and an
intercept of –108 dBV. The scaling parameters are supply-
and temperature-independent.
The AD8310 is available in the industrial temperature range of
–40°C to +85°C in an 8-lead MSOP package.
Rev. D
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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