AD8318 Datasheet, PDF (1/24 Pages) Analog Devices – 1 MHz - 8 GHz, 60 dB Logarithmic Detector/Controller

1 MHz – 8 GHz, 60 dB
Logarithmic Detector/Controller
AD8318
FEATURES
Wide bandwidth: 1 MHz to 8 GHz
High accuracy: ±1.0 dB over 55 dB range (f < 5.8 GHz)
Stability over temperature: ±0.5 dB
Low noise measurement/controller output VOUT
Pulse response time 10/12 ns (fall/rise)
Integrated temperature sensor
Small footprint CSP package
Power-down feature: <1.5 mW at 5 V
Single-supply operation: 5V @ 68 mA
Fabricated using high speed SiGe process
APPLICATIONS
RF transmitter PA setpoint control and level monitoring
RSSI measurement in base stations, WLAN, radar
GENERAL DESCRIPTION
The AD8318 is a demodulating logarithmic amplifier, capable of
accurately converting an RF input signal to a corresponding
decibel-scaled output voltage. It employs the progressive
compression technique over a cascaded amplifier chain, each
stage of which is equipped with a detector cell. The device can be
used in measurement or controller mode. The AD8318
maintains accurate log conformance for signals of 1 MHz to
6 GHz and provides useful operation to 8 GHz. The input range
is typically 60 dB (re: 50 Ω) with error less than ±1 dB. The
AD8318 has a 10 ns response time that enables RF burst
detection to beyond 60 MHz. The device provides
unprecedented logarithmic intercept stability versus ambient
temperature conditions. A 2 mV/K slope temperature sensor
output is also provided for additional system monitoring. A
single supply of +5 V is required. Current consumption is
typically 68 mA. Power consumption decreases to <1.5 mW
when the device is disabled.
The AD8318 can be configured to provide a control voltage to a
VGA, such as a power amplifier or a measurement output, from
pin VOUT. Since the output can be used for controller
FUNCTIONAL BLOCK DIAGRAM
TEMP
VPSI
ENBL
TADJ
TEMP
SENSOR
GAIN
BIAS
SLOPE
INHI
INLO
DET
DET
CMIP
DET DET
Figure 1.
VPSO
IV
VSET
IV
VOUT
CLPF
CMOP
applications, special attention has been paid to minimize
wideband noise. In this mode, the setpoint control voltage is
applied to VSET. The feedback loop through an RF
amplifier is closed via VOUT; the output of which regulates
the amplifier’s output to a magnitude corresponding to VSET.
The AD8318 provides 0 V to 4.9 V output capability at the
VOUT pin, suitable for controller applications. As a
measurement device, VOUT is externally connected to
VSET to produce an output voltage VOUT that is a decreasing
linear-in-dB function of the RF input signal amplitude.
The logarithmic slope is nominally −25 mV/dB, but can be
adjusted by scaling the feedback voltage from VOUT to the
VSET interface. The intercept is +20 dBm (re: 50 Ω, CW
input) using the INHI input. These parameters are very
stable against supply and temperature variations.
The AD8318 is fabricated on a SiGe bipolar IC process and
is available in a 4 mm × 4 mm, 16-pin LFCSP package, for
the operating temperature range of –40^oC to +85^oC.
Rev. 0
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: [phone]
www.analog.com
Fax: [phone] © 2003 Analog Devices, Inc. All rights reserved.