AD8347_15 Datasheet, PDF (1/28 Pages) Analog Devices – 0.8 GHz to 2.7 GHz Direct Conversion Quadrature Demodulator

0.8 GHz to 2.7 GHz Direct Conversion
Quadrature Demodulator
AD8347
FEATURES
Integrated RF and baseband AGC amplifiers
Quadrature phase accuracy 1° 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 to 5.5 V
Power-down mode
28-lead TSSOP package
APPLICATIONS
Cellular base stations
Radio links
Wireless local loop
IF broadband demodulators
RF instrumentation
Satellite modems
GENERAL DESCRIPTION
The AD8347¹ 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
quadrature accuracy and amplitude balance over the entire
operating frequency range. Separate I and 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.
FUNCTIONAL BLOCK DIAGRAM
LOIN 1
VPS1 2
IOPN 3
IOPP 4
VCMO 5
IAIN 6
COM3 7
IMXO 8
COM2 9
RFIN 10
RFIP 11
VPS2 12
IOFS 13
VREF 14
AD8347
PHASE
SPLITTER
PHASE
SPLITTER
DET
BIAS
GAIN
CONTROL
Figure 1.
28 LOIP
27 COM1
26 QOPN
25 QOPP
24 QAIN
23 COM3
22 QMXO
21 VPS3
20 VDT1
19 VAGC
18 VDT2
17 VGIN
16 QOFS
15 ENBL
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 are eliminated. Additional internal
circuitry also allows the user to set the dc common-mode level
at the baseband outputs.
1 _{U.S. patents issued and pending.}
Rev. A
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