AD9761 Datasheet, PDF (1/23 Pages) Analog Devices – Dual 10-Bit TxDAC+™ with 2x Interpolation Filters

a
Dual 10-Bit TxDAC+™
with 2؋ Interpolation Filters
AD9761
FEATURES
Complete 10-Bit, 40 MSPS Dual Transmit DAC
Excellent Gain and Offset Matching
Differential Nonlinearity Error: 0.5 LSB
Effective Number of Bits: 9.5
Signal-to-Noise and Distortion Ratio: 59 dB
Spurious-Free Dynamic Range: 71 dB
2؋ Interpolation Filters
20 MSPS/Channel Data Rate
Single Supply: +2.7 V to +5.5 V
Low Power Dissipation: 200 mW (+3 V Supply @
40 MSPS)
On-Chip Reference
28-Lead SSOP
PRODUCT DESCRIPTION
The AD9761 is a complete dual channel, high speed, 10-bit
CMOS DAC. The AD9761 has been developed specifically for
use in wide bandwidth communication applications (e.g., spread
spectrum) where digital I and Q information is being processed
during transmit operations. It integrates two 10-bit, 40 MSPS
DACs, dual 2× interpolation filters, a voltage reference, and
digital input interface circuitry. The AD9761 supports a
20 MSPS per channel input data rate that is then interpolated
by 2× up to 40 MSPS before simultaneously updating each
DAC.
The interleaved I and Q input data stream is presented to the
digital interface circuitry, which consists of I and Q latches as well
as some additional control logic. The data is de-interleaved back
into its original I and Q data. An on-chip state machine ensures the
proper pairing of I and Q data. The data output from each latch is
then processed by a 2× digital interpolation filter that eases the
reconstruction filter requirements. The interpolated output of each
filter serves as the input of their respective 10-bit DAC.
The DACs utilize a segmented current source architecture com-
bined with a proprietary switching technique to reduce glitch
energy and to maximize dynamic accuracy. Each DAC provides
differential current output thus supporting single-ended or
differential applications. Both DACs are simultaneously up-
dated and provide a nominal full-scale current of 10 mA. Also,
the full-scale currents between each DAC are matched to within
0.07 dB (i.e., 0.75%), thus eliminating the need for additional
gain calibration circuitry.
The AD9761 is manufactured on an advanced low cost CMOS
process. It operates from a single supply of 2.7 V to 5.5 V and
consumes 200 mW of power. To make the AD9761 complete it
also offers an internal 1.20 V temperature-compensated bandgap
reference.
TxDAC+ is a trademark of Analog Devices, Inc.
FUNCTIONAL BLOCK DIAGRAM
DCOM DVDD CLOCK ACOM AVDD
SLEEP
DAC DATA
INPUTS
(10 BITS)
WRITE INPUT
SELECT INPUT
LATCH
"I"
2؋
"I"
DAC
REFERENCE
LATCH
"Q"
MUX
CONTROL
BIAS
GENERATOR
2؋
"Q"
DAC
AD9761
IOUTA
IOUTB
REFLO
FSADJ
REFIO
COMP1
COMP2
COMP3
QOUTA
QOUTB
PRODUCT HIGHLIGHTS
1. Dual 10-Bit, 40 MSPS DACs: A pair of high performance
40 MSPS DACs optimized for low distortion performance
provide for flexible transmission of I and Q information.
2. 2× Digital Interpolation Filters: Dual matching FIR interpo-
lation filters with 62.5 dB stop band rejection precede each
DAC input thus reducing the DACs’ reconstruction filter
requirements.
3. Low Power: Complete CMOS Dual DAC function operates
on a low 200 mW on a single supply from 2.7 V to 5.5 V.
The DAC full-scale current can be reduced for lower power
operation, and a sleep mode is provided for power reduction
during idle periods.
4. On-Chip Voltage Reference: The AD9761 includes a 1.20 V
temperature-compensated bandgap voltage reference.
5. Single 10-Bit Digital Input Bus: The AD9761 features a
flexible digital interface allowing each DAC to be addressed
in a variety of ways including different update rates.
6. Small Package: The AD9761 offers the complete integrated
function in a compact 28-lead SSOP package.
7. Product Family: The AD9761 Dual Transmit DAC has a
pair of Dual Receive ADC companion products, the AD9281
(8 bits) and AD9201 (10 bits).
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
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© Analog Devices, Inc., 2000