REV.0
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may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices.
a
AD8347
*
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 www.analog.com
Fax: 781/326-8703 © Analog Devices, Inc., 2001
0.8 GHz–2.7 GHz
Direct Conversion Quadrature Demodulator
FUNCTIONAL BLOCK DIAGRAM
RFIN
VREF
RFIP
VPS2
IMXO
COM3
IOPP
IOFS
IOPN
VCMO
VPS1
LOIN
IAIN
COM2
VDT2
QMXO
QOPP
QOFS
QOPN
VAGC
COM3
VGIN
ENBL
LOIP
COM1
VDT1
QAIN
VPS3
28
27
26
25
24
23
22
21
20
19
18
17
16
15
1
2
3
4
5
6
7
8
9
10
11
12
13
14
AD8347
PHASE
SPLITTER
PHASE
SPLITTER
GAIN
CONTROL
BIAS
DET
FEATURES
Integrated RF and Baseband AGC Amplifiers
Quadrature Phase Accuracy 1H11543 Typ
I/Q Amplitude Balance 0.3 dB Typ
Third Order Intercept (IIP3) +11.5 dBm @ Min Gain
Noise Figure 11 dB @ Max Gain
AGC Range 69.5 dB
Baseband Level Control Circuit
Low LO Drive –8 dBm
ADC Compatible I/Q Outputs
Single Supply 2.7 V–5.5 V
Power-Down Mode
Package 28-Lead TSSOP
APPLICATIONS
Cellular Basestations
Radio Links
Wireless Local Loop
IF Broadband Demodulator
RF Instrumentation
Satellite Modems
GENERAL DESCRIPTION
The AD8347 is a broadband Direct Quadrature Demodulator
with RF and baseband Automatic Gain Control (AGC) amplifiers.
It is suitable for use in many communications receivers,
performing Quadrature demodulation directly to baseband
frequencies. The input frequency range is 800 MHz to 2.7 GHz.
The outputs can be connected directly to popular A-to-D converters
such as the AD9201 and AD9283.
The RF input signal goes through two stages of variable gain
amplifiers prior to two Gilbert-cell Mixers. The LO quadrature
phase splitter employs polyphase filters to achieve high quadra-
ture accuracy and amplitude balance over the entire operating
frequency range. Separate I & Q channel variable-gain amplifiers
follow the baseband outputs of the mixers. The RF and baseband
amplifiers together provide 69.5 dB of gain control. A precision
control circuit sets the Linear-in-dB RF gain response to the gain
control voltage.
Baseband level detectors are included for use in an AGC loop to
maintain the output level. The demodulator dc offsets are
minimized by an internal loop, whose time constant is controlled
by external capacitor values. The offset control can also be
overridden by forcing an external voltage at the offset nulling pins.
The baseband variable gain amplifier outputs are brought off-chip
for filtering before final amplification. By inserting a channel
selection filter before each output amplifier high-level out-of-
channel interferers can be eliminated. Additional internal circuitry
also allows the user to set the dc common-mode level at the
baseband outputs.
*U.S. Patents Issued and Pending