1 MHz to 8 GHz, 70 dB
Logarithmic Detector/Controller
AD8318
FUNCTIONAL BLOCK DIAGRAM
FEATURES
VPSI
ENBL
TADJ
VPSO
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 ns/12 ns (fall/rise)
Integrated temperature sensor
TEMP
SENSOR
GAIN
BIAS
TEMP
SLOPE
VSET
I
I
V
V
VOUT
CLPF
DET
DET
DET
DET
Small footprint LFCSP
INHI
Power-down feature: <1.5 mW at 5 V
Single-supply operation: 5 V @ 68 mA
Fabricated using high speed SiGe process
INLO
CMIP
CMOP
Figure 1.
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
6
APPLICATIONS
5
RF transmitter PA setpoint control and level monitoring
RSSI measurement in base stations, WLAN, WiMAX, and
radars
4
3
2
1
0
GENERAL DESCRIPTION
–1
–2
–3
–4
–5
–6
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 is
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 45 MHz. The device provides unprece-
dented logarithmic intercept stability vs. ambient temperature
conditions. A 2 mV/°C 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.
–65 –60 –55 –50 –45 –40 –35 –30 –25 –20 –15 –10 –5
0
5
10
P
(dBm)
IN
Figure 2. Typical Logarithmic Response and Error vs. Input Amplitude at 5.8 GHz
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 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, Pin VOUT is externally
connected to VSET to produce an output voltage, VOUT, which
is a decreasing linear-in-dB function of the RF input signal
amplitude.
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. Because the output can be used for controller
applications, wideband noise is minimal.
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-lead LFCSP for the operating
temperature range of –40oC to +85oC.
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 registeredtrademarks arethe property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113 ©2004-2007 Analog Devices, Inc. All rights reserved.
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