Modern wireless system design is usually
a team effort, with RF engineers
working on the front end and the
baseband guys working on the digital
back end. The trouble in receiver
design, though, is at the interface where
the downconverted signal at some IF
must then be digitized and sent to the
baseband section. This is a tricky area
that neither the RF nor baseband engineers
are generally prepared to attack. A
mixed-signal expert is usually needed to
build the critical interface.
With IFs well into the many megahertz
range, special differential amplifier to converter matching circuits and critical
printed-circuit board (PCB) layouts
are required. Recognizing this problem,
Linear Technology has come up with an
IF receiver module that eliminates the
need to design that special interface. The
LTM9001 implements the signal chain
from the filtered and downconverted IF
to the analog-to-digital converter (ADC)
output (see the figure).
This system-in-a-package (SiP) module
consists of a differential input amplifier
with a gain of 20 dB, a 162.5-MHz
LC bandpass filter with a bandwidth of
50 MHz for anti-aliasing, and a 16-bit,
130-Msample/s ADC all on a common
die in a land-grid array (LGA) package
of 11.25 by 11.25 mm. Additionally, it
includes all bypass capacitors and other
needed discretes.
The amplifierâ??s input impedance is
available in 50-, 200-, or 400-Ω versions.
The ADCâ??s signal-to-noise ratio (SNR)
is 72 dB, and its spurious-free dynamic
range (SFDR) is 82 dB. The ADC outputs
are either CMOS or low-voltage
differential signaling (LVDS), pin selectable.
The module operates from a 3.3-V
supply and dissipates 1.65 W.
The really great news about this product
is that it will be available in custom
form. For example, you can select the
input amplifier gain from 8-, 14-, 20-,
or 26-dB choices. The IF range may be
up to 300 MHz, and the ADC can be
had in sampling rates from 10 to 160
Msamples/s. The anti-alias filter may
also be a bandpass or low pass.
If youâ??re designing high-end basestations,
satellite communications receivers,
special communications receivers,
spectrum analyzers, or other wireless test
gear, the LTM9001 is worth an evaluation.
Available now, it costs $82 in quantities
of 1000 units. Contact the company
for more details and quotes on your
custom needs.
LINEAR TECHNOLOGIES
www.linear.com
