For portable applications as diverse
as medical imaging units, professional
video cameras, batterypowered
software-defined radios,
and industrial test and measurement
designs, the 14-bit,
125-Msample/s LTC2261 analogto-
digital converter (ADC) from
Linear Technology dissipates
127 mW—less than one-third
the power of alternative chips.
The company acknowledges
that much of the power savings
arises from running the
LTC2261 at 1.8 V (see the figure).
But Linear also points out
that its engineers achieved that low-voltage operation without
sacrificing ac performance. This ADC offers signal-to-noise
ratio (SNR) performance of 73.4 dB and spurious free dynamic
range (SFDR) of 85 dB at baseband. Ultra-low jitter of 0.17
psRMS enables the undersampling of IF frequencies with
excellent noise performance.
Other helpful features include a data randomizer that simplifies
life for designers routing digital outputs on circuit
boards. With high-speed ADCs, it’s often hard to avoid digital
noise coupling back and distorting the analog reading. When
that happens, interference from digital feedback is visible as
unwanted tones in the ADC output spectrum. By randomizing
the digital output, the LTC2261 reduces the amplitude of these
unwanted tones by spreading this energy into the noise floor.
This can reduce the digital feedback effect by 10 to 15 dB.
The LTC2261’s digital outputs can be set to full-rate CMOS,
double-data-rate (DDR) CMOS, or DDR low-voltage differential
signaling (LVDS). DDR outputs reduce the number of data
lines needed by half. A separate output power supply allows the
CMOS output swing to range from 1.2 to 1.8 V. There’s also a
clock duty cycle stabilizer circuit to facilitate non-50% clock
duty cycles, programmable digital output timing, programmable
LVDS output current, and optional LVDS output termination.
These features combine to make the data transmission
between the ADC and the microcontroller more flexible.
Still, the main focus of the LTC2261 and its sister parts is the
marriage of low power at lithium-cell voltages with high performance,
lowering the power budget for high-speed data acquisition
and making it possible to “cut the cord” and migrate products
into the portable world. Supporting that is the device’s
6- by 6-mm quad flat no-lead (QFN) packaging.
The LTC2261 family parts that comprises six pin-compatible
members, offering 14-bit resolution at 125, 105, and
80 Msamples/s and 12-bit resolution at 125, 105, and 80
Msamples/s. Pricing starts at $9.50 each.
DON TUITE
LINEAR TECHNOLOGYwww.linear.com