Meeting the need for analog-to-digital converter (ADC) sampling at
rates beyond 135 Msamples/s in WiMAX applications, Analog Devices'
AD9640 is the first dual 14-bit analog-todigital converter (ADC) to offer 150 Msamples/s. It provides two ADCs in the same
footprint as previous single ADCs with the
same performance. Also, it offers an onchip clock divider and digital inputs to the
receiver-system automatic gain control
(AGC) circuitry ().
That AGC block monitors the incoming
composite signal power so receivers that
use the chip can implement fast or slow
AGC. "Slow" mode is for conventional
AGC. "Fast detect" (FD) mode enables
the system to detect an input over-range
condition in as little as two clock cycles
so it can immediately reduce gain to
avoid overdriving the analog front end. In
addition to providing clipping information, the FD bits have programmable
thresholds that are useful in optimizing
the receiver AGC loop.
The on-chip clock divider in the
AD9640 simplifies system layout and
takes another chip off the board. In
basestation transmitters, the digital-toanalog converters (DACs) usually operate
at a higher clock rate than the ADC, and
the DAC clock is divided down for the
ADC. By implementing the clock divider
on-chip, the AD9640 eliminates the need
for an external divider.
Besides WiMAX, the AD9640 can support W-CDMA, cdma2000, and TDSCDMA. Sampling now, production quantities will be available in April. It will be
available in 12- and 14-bit resolutions
with sample rates of 80, 105, 125, and
150 Msamples/s.
In 1000-piece lots, 14-bit versions of
the AD9604 cost between $37.50 and
$87.50, and 12-bit versions cost between
$25.05 and $47.97, depending on sample rate.
Analog Devices
www.analog.com