1 MHz to 10 GHz, 50 dB
Log Detector/Controller
AD8317
Rev. 0
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FEATURES
Wide bandwidth: 1 MHz to 10 GHz
High accuracy: ±1.0 dB over temperature
50 dB dynamic range up to 8 GHz
Stability over temperature ±0.5 dB
Low noise measurement/controller output VOUT
Pulse response time: 8/10 ns (fall/rise)
Small footprint 2 mm x 3 mm CSP package
Supply operation: 3.0 V to 5.5 V @ 22 mA
Fabricated using high speed SiGe process
APPLICATIONS
RF transmitter PA setpoint control and level monitoring
Power monitoring in radiolink transmitters
RSSI measurement in base stations, WLAN, WiMAX, radar
GENERAL DESCRIPTION
The AD8317 is a demodulating logarithmic amplifier, capable
of accurately converting an RF input signal to a corresponding
decibel-scaled output. 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
either measurement or controller modes. The AD8317 maintains
accurate log conformance for signals of 1 MHz to 8 GHz and
provides useful operation to 10 GHz. The input dynamic range
is typically 50 dB (re: 50 ) with error less than ±1 dB. The AD8317
has 8/10 ns response time (fall time/rise time) that enables RF
burst detection to a pulse rate of beyond 50 MHz. The device
provides unprecedented logarithmic intercept stability vs. ambient
temperature conditions. A supply of 3.0 V to 5.5 V is required to
power the device. Current consumption is typically 22 mA, and it
decreases to 200 A when the device is disabled.
The AD8317 can be configured to provide a control voltage to
a power amplifier or a measurement output from the VOUT
pin. Because the output can be used for controller applications,
special
attention has been paid to minimize wideband noise. In this
mode, the setpoint control voltage is applied to the VSET pin.
FUNCTIONAL BLOCK DIAGRAM
GAIN
BIAS
SLOPE
DET DET DET DET
INHI
INLO
IV
VOUT
IV
VSET
CLPF
TADJVPOS
COMM
05541-001
Figure 1.
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 V
SET
. The AD8317 provides 0 V to (V
POS
− 0.1 V)
output capability at the VOUT pin, suitable for controller applica-
tions. As a measurement device, VOUT is externally connected to
VSET to produce an output voltage V
OUT
that is a decreasing
linear-in-dB function of the RF input signal amplitude.
The logarithmic slope is −22 mV/dB, determined by the VSET
interface. The intercept is +15 dBm (re: 50 Ω, CW input) using
the INHI input. These parameters are very stable against supply
and temperature variations.
The AD8317 is fabricated on a SiGe bipolar IC process and is
available in a 2 mm × 3 mm, 8-lead LFCSP_VD package for an
operating temperature range of −40
o
C to +85
o
C.
