What's more important in new product announcements-
new levels of performance, or the availability
of design tools that make those performance levels
accessible? Many designers no longer have the luxury of enough
development time to breadboard, refine, and test circuits assembled
from parts from multiple chip vendors-assuming designers
aren't paying too much of a premium for what the marketing
people call a "platform" or a "solution."
During a recent product briefing with National Semiconductor,
I asked the company rep about the importance of the new
products' reference designs. "Are they really vital, or are they
just sales gimmicks?" I asked.
"No gimmicks," the representative said. "The
designers are as proud of them as they are of the
parts themselves."
"Then lead with the reference designs," I said. But
of course, that didn't happen. Instead, I learned that
the new parts are three energy-efficient, high-speed
differential amplifiers that respectively target communications,
test and instrumentation, and defense and space
applications. Energy efficiency is their claim to fame, so
National has tagged the line "PowerWise" (see the figure).
National quickly moved to a description of the three reference
designs: one for WiMAX and 2G/3G wireless basestations,
one for test and measurement equipment, and one for
high-speed communications systems. National's WaveVision
hardware and software, application specifications, schematic
diagrams, bills of materials, and layout guidelines all support
the boards.
The LMH6552 is a 1.5-GHz, current-feedback differential
amplifier that consumes 112 mW. The LMH6515 is a digitally
controlled variable-gain amplifier (DVGA) with an 8-dB noise
figure and a 40-dBm output intercept point (OIP3) at 70 MHz,
with similarly low power consumption. The LMH6555 differential
amp suits signal conditioning ahead of an 8-bit,
3-Gsample/s data-acquisition system.
The reference designs
The first reference design is
a low-IF receiver subsystem that uses a pair of LMH6552 differential
drivers and a dual analog-to-digital converter (ADC) for
quadrature direct conversion or for a near zero-IF receiver for
signal frequencies from dc to 40 MHz.
With a 1-GHz input bandwidth for the ADC, the design
achieves 73.3 dBFS and a signal-to-noise ratio (SNR) better
than 85 dBFS. The ADC is National's ADC14DS105 dual,
14-bit, 105-Msample/s differential-out chip. Other components
include a low-jitter clock conditioner and several power-
management ICs.
The high-IF receiver reference design highlights the Power-
Wise DVGA and National's ADC14V155 14-bit, 155-Msample/s
ADC. In a wireless infrastructure system or digital spectrum
analyzer, it would provide variable-gain IF amplification
and digitization. Small-signal SNR is 72 dBFS, and
spurious-free dynamic range (SFDR) is greater than
90 dBFS with a 169-MHz input.
Large-signal SNR is 68.3 dBFS, with a 77-dBFS SFDR at
169 MHz. Other chips on the board include a low-jitter precision
clock conditioner with an integrated voltage-controlled
oscillator (VCO) that provides 190-fs jitter over an integration
bandwidth of 100 Hz to 20 MHz, as well as those power-management
ICs.
The final reference design is an 8-bit, 3-Gsample/s dataacquisition
board for test and measurement equipment and
the kind of very high-speed communications systems used in
defense and space applications. It receives an ac- or dc-coupled
analog input and captures the digital output of the ADC
into an FPGA. For evaluation, the captured data can be analyzed
using National's WaveVision software on a Windows PC
via a USB 2.0 connection.
When ac-coupled, the board achieves better than 7-bit
effective number of bits (ENOB) and 53.5-dB SFDR at frequencies
up to 1.4 GHz. The ADC is National's ADC083000
8-bit, 3-Gsample/s performer. Also on the board is the
LMX2531 single-chip phase-locked loop/VCO, which provides
â??116-dBc/Hz phase noise at a 100-kHz offset.
How "PowerWise" are the boards? The high-IF reference
design draws a bit over 600 mA at 5 V; the low-IF draws around
500 mA; and the data-acquisition board draws approximately
600 mA at 12 V.
Pricing
In 1000-unit lots, the LMH6515 costs $5.25
each and the LMH6552 is $3.95. The LMH6555 costs $5.95
each in 100-unit lots. The ADC14V155KDRB (High-IF) and
ADC14DS105KARB (Low-IF) receiver reference-design boards
cost $800 each. The 3-Gsample/s ADC083000RB dataacquisition
board costs $4900.
National Semiconductor
www.national.com