AD8313 Datasheet, PDF (1/16 Pages) Analog Devices – 0.1 GHz-2.5 GHz, 70 dB Logarithmic Detector/Controller

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0.1 GHz–2.5 GHz, 70 dB
Logarithmic Detector/Controller
AD8313
FEATURES
Wide Bandwidth: 0.1 GHz to 2.5 GHz Min
High Dynamic Range: 70 dB to ؎3.0 dB
High Accuracy: ؎1.0 dB over 65 dB Range (@ 1.9 GHz)
Fast Response: 40 ns Full-Scale Typical
Controller Mode with Error Output
Scaling Stable Over Supply and Temperature
Wide Supply Range: +2.7 V to +5.5 V
Low Power: 40 mW at 3 V
Power-Down Feature: 60 ␮W at 3 V
Complete and Easy to Use
APPLICATIONS
RF Transmitter Power Amplifier Setpoint
Control and Level Monitoring
Logarithmic Amplifier for RSSI Measurement
Cellular Base Stations, Radio Link, Radar
PRODUCT DESCRIPTION
The AD8313 is a complete multistage demodulating logarith-
mic amplifier, capable of accurately converting an RF signal at
its differential input to an equivalent decibel-scaled value at its
dc output. The AD8313 maintains a high degree of log con-
formance for signal frequencies from 0.1 GHz to 2.5 GHz and
is useful over the range of 10 MHz to 3.5 GHz. The nominal
input dynamic range is –65 dBm to 0 dBm (re: 50 Ω), and the
sensitivity can be increased by 6 dB or more with a narrow band
input impedance matching network or balun. Application is
straightforward, requiring only a single supply of 2.7 V–5.5 V
and the addition of a suitable input and supply decoupling.
Operating on a 3 V supply, its 13.7 mA consumption (for T_A =
+25°C) amounts to only 41 mW. A power-down feature is
provided; the input is taken high to initiate a low current
(20 µA) sleep mode, with a threshold at half the supply voltage.
The AD8313 uses a cascade of eight amplifier/limiter cells,
each having a nominal gain of 8 dB and a –3 dB bandwidth of
3.5 GHz, for a total midband gain of 64 dB. At each amplifier
output, a detector (rectifier) cell is used to convert the RF signal
to baseband form; a ninth detector cell is placed directly at the
input of the AD8313. The current-mode outputs of these cells
are summed to generate a piecewise linear approximation to the
logarithmic function, and converted to a low impedance voltage-
mode output by a transresistance stage, which also acts as a low-
pass filter.
VPOS
INHI
INLO
VPOS
FUNCTIONAL BLOCK DIAGRAM
NINE DETECTOR CELLS
+
+
+
+
+ IvV
8dB
8dB
C_INT
8dB
8dB ^LP _VvI
EIGHT 8dB 3.5GHz AMPLIFIER STAGES
AD8313
INTERCEPT
CONTROL
SLOPE
CONTROL
BAND-GAP
REFERENCE
GAIN
BIAS
VOUT
VSET
COMM
PWDN
When used as a log amp, the scaling is determined by a separate
feedback interface (a transconductance stage) that sets the slope
to approximately 18 mV/dB; used as a controller, this stage
accepts the setpoint input. The logarithmic intercept is posi-
tioned to nearly –100 dBm, and the output runs from about
0.45 V dc at –73 dBm input to 1.75 V dc at 0 dBm input. The
scale and intercept are supply and temperature stable.
The AD8313 is fabricated on Analog Devices’ advanced
25 GHz silicon bipolar IC process and is available in a 8-lead
µSOIC package. The operating temperature range is –40°C to
+85°C. An evaluation board is available.
2.0
5
FREQUENCY = 1.9GHz
1.8
4
1.6
3
1.4
2
1.2
1
1.0
0
0.8
–1
0.6
–2
0.4
–3
0.2
–4
0
–5
–80 –70 –60 –50 –40 –30 –20 –10
0
INPUT AMPLITUDE – dBm
Figure 1. Typical Logarithmic Response and Error vs.
Input Amplitude
REV. B
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© Analog Devices, Inc., 1999