a
FEATURES
Multistage Demodulating Logarithmic Amplifier
Voltage Output, Rise-Time <15 ns
High-Current Capacity: 25 mA into Grounded R
L
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 A Sleep Current
APPLICATIONS
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
Signal-Level Determination Down to 20 Hz
True-Decibel AC Mode for Multimeters
Fast, Voltage-Out DC-440 MHz
95 dB Logarithmic Amplifier
AD8310
FUNCTIONAL BLOCK DIAGRAM
AD8310
8mA
BANDGAP REFERENCE
AND BIASING
SIX 14.3dB 900MHz
AMPLIFIER STAGES
MIRROR
3
NINE DETECTOR CELLS
SPACED 14.3dB
COMMON
COMM
INPUT-OFFSET
COMPENSATION LOOP
2
2 A
/dB
3k
COMM
+
–
3k
1k
OFLT
33pF
COMM
OFFSET
FILTER
VOUT
OUTPUT
ENBL
ENABLE
BUFFER
INPUT
VPOS
SUPPLY
BFIN
+INPUT
–INPUT
INHI
1.0k
INLO
COMM
PRODUCT 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 consump-
tion of only 24 mW at 3 V. A fast-acting CMOS-compatible
enable pin is provided.
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 ampli-
tude of a 1 V rms sine wave) that is, an amplitude of about
±
40
µV,
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 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 to –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 is somewhat greater at 440 MHz. There
is no minimum frequency limit; the AD8310 may be used down
to low audio frequencies. Special filtering features are provided
to support this wide range.
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, small 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 requiring the reduction
of a signal to its decibel equivalent.
The AD8310 is available in the industrial temperature range of
–40°C to +85°C, in an 8-lead Mini_SO package.
REV. A
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1999
AD [ ANALOG DEVICES ]
