AD8318_06 Datasheet, PDF (1/24 Pages) Analog Devices – 1 MHz to 8 GHz, 60 dB Logarithmic Detector/Controller

1 MHz to 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 ns/12 ns (fall/rise)
Integrated temperature sensor
Small footprint CSP package
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 radar
TEMP
FUNCTIONAL BLOCK DIAGRAM
VPSI
ENBL
TADJ
VPSO
TEMP
SENSOR
GAIN
BIAS
SLOPE
IV
VSET
INHI
INLO
DET
DET
CMIP
DET DET
Figure 1.
IV
VOUT
CLPF
CMOP
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.
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 magni-
tude 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 package, for the
operating temperature range of –40^oC to +85^oC.
Rev. A
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