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AD8318 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer AD8318
Beschreibung Logarithmic Detector/Controller
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 25 Seiten
AD8318 Datasheet, Funktion
1 MHz to 8 GHz, 70 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 ns/12 ns (fall/rise)
Integrated temperature sensor
Small footprint LFCSP
Power-down feature: <1.5 mW at 5 V
Single-supply operation: 5 V @ 68 mA
Fabricated using high speed SiGe process
APPLICATIONS
RF transmitter PA setpoint control and level monitoring
RSSI measurement in base stations, WLAN, WiMAX, and
radars
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 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.
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.
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.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
TEMP
FUNCTIONAL BLOCK DIAGRAM
VPSI
ENBL
TADJ
VPSO
TEMP
SENSOR
GAIN
BIAS
SLOPE
IV
VSET
INHI
INLO
DET
DET
DET
DET
IV
VOUT
CLPF
CMIP
Figure 1.
CMOP
2.4 6
2.2 5
2.0 4
1.8 3
1.6 2
1.4 1
1.2 0
1.0 –1
0.8 –2
0.6 –3
0.4 –4
0.2 –5
0 –6
–65 –60 –55 –50 –45 –40 –35 –30 –25 –20 –15 –10 –5 0 5 10
PIN (dBm)
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 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.
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.






AD8318 Datasheet, Funktion
Parameter
VSET INTERFACE
Nominal Input Range
Logarithmic Scale Factor
Bias Current Source
TEMPERATURE REFERENCE
Output Voltage
Temperature Slope
Current Source/Sink
POWER-DOWN INTERFACE
Logic Level to Enable Device
ENBL Current When Enabled
ENBL Current When Disabled
POWER INTERFACE
Supply Voltage
Quiescent Current
vs. Temperature
Supply Current when Disabled
vs. Temperature
Conditions
VSET (Pin 7)
PIN = 0 dBm; measurement mode2
PIN = −65 dBm; measurement mode2
PIN = −10 dBm; VSET = 2.1 V
TEMP (Pin 13)
TA = 25°C, RLOAD = 10 kΩ
−40°C ≤ TA +85°C, RLOAD = 10 kΩ
TA = 25°C
ENBL (Pin 16)
ENBL = 5 V
ENBL = 0 V; sourcing
VPSI (Pin 3 and Pin 4), VPSO (Pin 9)
ENBL = 5 V
−40°C ≤ TA ≤ +85°C
ENBL = 0 V, total currents for VPSI and VPSO
−40°C ≤ TA ≤ +85°C
1 Controller mode.
2 Gain = 1. For other gains, see the Measurement Mode section.
AD8318
Min Typ
0.5
2.1
−0.04
2.5
0.57 0.6
2
10/0.1
1.7
<1
15
4.5 5
50 68
150
260
350
Max Unit
V
dB/mV
μA
0.63 V
mV/°C
mA
V
μA
μA
5.5 V
82 mA
μA/°C
μA
μA
Rev. B | Page 5 of 24

6 Page









AD8318 pdf, datenblatt
THEORY OF OPERATION
The AD8318 is a 9-stage demodulating logarithmic amplifier
that provides RF measurement and power amplifier control
functions. The design of the AD8318 is similar to the AD8313
logarithmic detector/controller. However, the AD8318 input
frequency range extends to 8 GHz with a 60 dB dynamic range.
Other improvements include: reduced intercept variability vs.
temperature, increased dynamic range at higher frequencies,
low noise measurement and controller output (VOUT),
adjustable low-pass corner frequency (CLPF), temperature
sensor output (TEMP), negative transfer function slope for
higher accuracy, and 10 ns response time for RF burst detection
capability. A block diagram is shown in Figure 22.
VPSI
ENBL
TADJ
VPSO
TEMP
TEMP
SENSOR
GAIN
BIAS
SLOPE
IV
VSET
INHI
INLO
DET
DET
DET
DET
IV
VOUT
CLPF
CMIP
Figure 22. Block Diagram
CMOP
A fully differential design, using a proprietary high speed SiGe
process, extends high frequency performance. Input INHI
receives the signal with a low frequency impedance of nominally
1200 Ω in parallel with 0.7 pF. The maximum input with ±1 dB
log conformance error is typically 0 dBm (re: 50 Ω). The noise
spectral density referred to the input is 1.15 nV/Hz, which is
equivalent to a voltage of 118 μV rms in a 10.5 GHz bandwidth,
or a noise power of −66 dBm (re: 50 Ω). This noise spectral
density sets the lower limit of the dynamic range. However, the
low end accuracy of the AD8318 is enhanced by specially
shaping the demodulating transfer characteristic to partially
compensate for errors due to internal noise.
AD8318
CMIP, the input system common pin, provides a quality low
impedance connection to the printed circuit board (PCB)
ground via four package pins. Ground the package paddle,
which is internally connected to the CMIP pin, to the PCB to
reduce thermal impedance from the die to the PCB.
The logarithmic function is approximated in a piecewise
fashion by nine cascaded gain stages. For a more complete
explanation of the logarithm approximation, refer to the
AD8307 data sheet. The cells have a nominal voltage gain of
8.7 dB each and a 3 dB bandwidth of 10.5 GHz.
Using precision biasing, the gain is stabilized over temperature
and supply variations. Because the cascaded gain stages are
dc-coupled, the overall dc gain is high. An offset compensation
loop is included to correct for offsets within the cascaded cells.
At the output of each of the gain stages, a square-law detector
cell rectifies the signal. The RF signal voltages are converted to a
fluctuating differential current with an average value that
increases with signal level. Along with the nine gain stages and
detector cells, an additional detector is included at the input of
the AD8318, altogether providing a 60 dB dynamic range. After
the detector currents are summed and filtered, the function
ID × log10(VIN/VINTERCEPT)
(1)
is formed at the summing node,
where:
ID is the internally set detector current.
VIN is the input signal voltage.
VINTERCEPT is the intercept voltage (that is, when VIN = V ,INTERCEPT
the output voltage would be 0 V if capable of going to 0 V).
Rev. B | Page 11 of 24

12 Page





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