Integrated I/Q demodulator with IF VGA amplifier
Operating IF frequency 50 MHz to 1000 MHz
(3 dB IF BW of 500 MHz driven from RS = 200 Ω)
Demodulation bandwidth 75 MHz
Linear-in-decibel AGC range 44 dB
IIP3 +28 dBm @ minimum gain (FIF = 380 MHz)
IIP3 −8 dBm @ maximum gain (FIF = 380 MHz)
Quadrature demodulation accuracy
Phase accuracy 0.5°
Amplitude balance 0.25 dB
Noise figure 11 dB @ maximum gain (FIF = 380 MHz)
LO input −10 dBm
Single supply 2.7 V to 5.5 V
Compact, 28-lead TSSOP package
Wireless local loop
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
are designed to interface directly with dual-channel ADCs, such
as the AD9201, AD9283, and AD9218, for digitizing and post-
The IF input signal is fed into two Gilbert cell mixers through
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-
acteristic for the VGA and provides temperature compensation.
The LO quadrature phase splitter employs a divide-by-2 frequency
divider to achieve high quadrature accuracy and amplitude balance
over the entire operating frequency 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 the MXIP and MXIN pins.
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
50 MHz to 1000 MHz
FUNCTIONAL BLOCK DIAGRAM
MXIP MXIN ENVG
Separate I- and Q-channel baseband amplifiers follow the baseband
outputs of the mixers. The voltage applied to the VCMO pin sets
the dc common-mode voltage level at the baseband outputs.
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 ADC.
Connecting a bypass capacitor at each offset compensation input
(IOFS and 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 I/Q baseband amplifiers. The single-ended mixer output is
amplified and converted to a differential signal for driving ADCs.
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