50 MHz to 1000 MHz
Quadrature Demodulator
AD8348
FEATURES FUNCTIONAL BLOCK DIAGRAM
VREF IMXO IOFS IAIN IOPP IOPN
Integrated I/Q demodulator with IF VGA amplifier
14 8 13 6 4 3
Operating IF frequency 50 MHz to 1000 MHz
BIAS
VREF
ENBL 15
CELL
(3 dB IF BW of 500 MHz driven from R = 200 )
S
5 VCMO
Demodulation bandwidth 75 MHz
VCMO
DIVIDE 1 LOIP
Linear-in-decibel AGC range 44 dB
BY 2
IFIP 11
PHASE
Third-order intercept
IFIN 10
SPLITTER
28 LOIN
IIP3 +28 dBm @ minimum gain (FIF = 380 MHz)
AD8348
IIP3 8 dBm @ maximum gain (FIF = 380 MHz)
GAIN
VGIN 17
CONTROL
Quadrature demodulation accuracy
VCMO
Phase accuracy 0.5
18 19 24 21 16 23 25 26
MXIP MXIN ENVG QXMO QOFS QAIN QOPP QOPN
Amplitude balance 0.25 dB
Figure 1.
Noise figure 11 dB @ maximum gain (F = 380 MHz)
IF
LO input 10 dBm
Single supply 2.7 V to 5.5 V
Power-down mode
Compact, 28-lead TSSOP package
APPLICATIONS
QAM/QPSK demodulator
W-CDMA/CDMA/GSM/NADC
Wireless local loop
LMDS
GENERAL DESCRIPTION
The AD8348 is a broadband quadrature demodulator with an Separate I- and Q-channel baseband amplifiers follow the baseband
integrated intermediate frequency (IF), variable gain amplifier outputs of the mixers. The voltage applied to the VCMO pin sets
(VGA), and integrated baseband amplifiers. It is suitable for use in the dc common-mode voltage level at the baseband outputs.
communications receivers, performing quadrature demodulation Typically, VCMO is connected to the internal VREF voltage, but
from IF directly to baseband frequencies. The baseband amplifiers it can also be connected to an external voltage. This flexibility
are designed to interface directly with dual-channel ADCs, such allows the user to maximize the input dynamic range to the ADC.
as the
AD9201, AD9283, and AD9218, for digitizing and post- Connecting a bypass capacitor at each offset compensation input
processing. (IOFS and QOFS) nulls dc offsets produced in the mixer. Offset
compensation can be overridden by applying an external voltage
The IF input signal is fed into two Gilbert cell mixers through
at the offset compensation inputs.
an X-AMP VGA. The IF VGA provides 44 dB of gain control.
A precision gain control circuit sets a linear-in-decibel gain char- The mixers outputs are brought off-chip for optional filtering
acteristic for the VGA and provides temperature compensation. before final amplification. Inserting a channel selection filter
The LO quadrature phase splitter employs a divide-by-2 frequency before each baseband amplifier increases the baseband amplifiers
divider to achieve high quadrature accuracy and amplitude balance signal handling range by reducing the amplitude of high level,
over the entire operating frequency range. out-of-channel interferers before the baseband signal is fed into
the I/Q baseband amplifiers. The single-ended mixer output is
Optionally, the IF VGA can be disabled and bypassed. In this
amplified and converted to a differential signal for driving ADCs.
mode, the IF signal is applied directly to the quadrature mixer
inputs via the MXIP and MXIN pins.
Rev. A
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Last Content Update: 02/23/2017
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AN-924: Digital Quadrature Modulator Gain
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