AD8348 Datasheet, PDF (1/13 Pages) Analog Devices – 50-1000 MHz Quadrature Demodulator

PRELIMINARY TECHNICAL DATA
a
50–1000 MHz
Quadrature Demodulator
Preliminary Technical Data
AD8348
Features
Integrated I/Q demodulator with IF VGA Amplifier
Operating IF Frequency 50–1000 MHz
(3dB IF BW of 500MHz driven from Rs=200ohms)
Demodulation Bandwidth 60MHz
Linear-in-dB AGC Range 45dB
Third Order Intercept
IIP3 +26 dBm @ min gain (FIF=450MHz)
IIP3 -7 dBm @ max gain (FIF=450MHz)
Quadrature Demodulation Accuracy
Phase Accuracy 0.6^o RMS
Amplitude Balance 0.3 dB
Noise Figure 12.5dB @ max gain (FIF=500MHz)
LO Input -10 dBm
Single Supply 2.7-5.5V
Power down mode
Compact 28-pin TSSOP package
Applications
QAM/QPSK Demodulator
W-CDMA/CDMA/GSM/NADC
Wireless Local Loop
LMDS/MMDS
General Description
The AD8348 is a broadband quadrature demodulator with an
integrated intermediate frequency (IF) variable-gain amplifier
(VGA) and integrated baseband amplifiers. It is suitable for
use in communications receivers, performing quadrature
demodulation from IF directly to baseband frequencies. The
baseband amplifiers have been designed to directly interface
with dual channel A-to-D converters such as the AD9201,
AD9283, and AD9218 for digitizing and post-processing.
The IF input signal is fed into two Gilbert-cell mixers through
an X-AMP VGA. The IF VGA provides 45dB of gain
control. A precision gain-control circuit sets a linear-in-dB
gain characteristic for the VGA and provides temperature
compensation. The LO quadrature phase splitter employs a
divide-by-two frequency divider to achieve high quadrature
accuracy and amplitude balance over the entire operating fre-
quency range.
Optionally, the IF VGA can be disabled and bypassed. In this
mode, the IF signal is applied directly to the quadrature mixer
inputs via pins MXIP and MXIN.
Functional Block Diagram
Separate I & Q-channel baseband amplifiers follow the
baseband outputs of the mixers. The DC common-mode
voltage level at the baseband outputs is set by the voltage
applied to the VCMO pin. Typically VCMO is connected to
the internal VREF voltage but it can also be connected to an
external voltage. This flexibility allows the user to maximize
the input dynamic range to the A-to-D converter. Connecting
a bypass capacitor at each offset compensation input (IOFS &
QOFS) nulls DC offsets produced in the mixer. Offset
compensation can be overridden by applying an external
voltage at the offset compensation inputs.
The mixers’ outputs are brought off-chip for optional filtering
before final amplification. Inserting a channel selection filter
before each baseband amplifier increases the baseband
amplifiers’ signal handling range by reducing the amplitude of
high-level, out-of-channel interferers before the baseband
signal is fed into the baseband amplifiers. The single-ended
mixer output is amplified and converted to a differential signal
for driving ADCs.
Rev. PrF 2/11/03
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