Single/dual-channel wideband passive mixers
for communications apps
Analog Devices, Inc. has introduced ADL5811 single-channel
and ADL5812 dual-channel wideband passive mixers for communications
applications. The ADL5811 single-channel and ADL5812 dual-channel
mixers designed to deliver high linearity, low distortion
and low noise for a wide range of frequency band. The new
devices can be used for designing multiband, single-board
receivers by combining a wideband LO (local oscillator)
amplifier, a programmable RF balun, a high-linearity mixer
core, a programmable IF filter, and an IF amplifier.
ADI's new passive mixers extend across a 700-MHz to 2800-MHz
frequency range in a single device while delivering input
IP3 (third order intercept) of 24 dBm, an 11 dB SSB noise
figure and 7 dB of power conversion gain. These performance
specifications are maintained across the full operating
frequency range. The ADL5811 and ADL5812 passive mixers
are designed for wideband wireless infrastructure applications
and software-defined radio applications, including multi-band/multi-standard
cellular base station receivers, wideband radio link down
converters, multi-mode cellular repeaters, and picocells
applications.
"Wireless receiver designers typically have had to
choose between an active mixer, which offers excellent wideband
operation and moderate spurious-free dynamic range, or a
passive mixer, which has greater SFDR performance but much
narrower operating bandwidth," said Peter Real, vice
president, Linear and RF products, Analog Devices. "The
ADL5811 and ADL5812 passive mixers eliminate the need for
this trade off by giving engineers the linearity, distortion
and noise performance they need while also supporting true
wideband frequency operation."
ADI says the high performance across 700 MHz to 2800 MHz
of the new passive mixers is the result of three technical
advances, most significantly the development of a limiting
LO amplifier capable of generating a high-voltage, fast-rise-time,
square wave over a wide bandwidth with no DC current penalty
compared to existing narrow band mixers. The second technique
involves the integration of a tuned,RF balun structure to
ensure a well-balanced RF signal is applied to the FET mixer.
Previously, narrowband mixers incorporated an RF balun consisting
of a magnetic or transmission line transformer, which provided
low loss but only moderate bandwidth, according to ADI.
A third technique addresses the potential for the passive
mixer's structure to generate a composite signal that could
result in the early compression of the IF amplifier. ADI
said it has reduced the amplitude of the unwanted sideband
into a load by designing a tuned filter network to provide
the proper sum termination as a function of the RF and LO
frequencies.
The frequencies of the ADL5811 and ADL5812 can be changed
using a three-wire SPI (serial port interface), which allows
designers to tune the mixers with no need for external impedance
matching components. Performance can be further optimized
by digitally adjusting the DC bias voltage to the passive
mixer gates. To minimize power dissipation, each channel
of the dual-channel ADL5812 can be enabled or disabled independent
of the other. For DPD (digital pre-distortion) transmit
observation receivers or non-diversity applications, the
single-channel ADL5811 can implement a single receiver chain
in a multi-channel or multi-band platform.