AD9861 Analog Devices, AD9861 Datasheet - Page 26

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AD9861

Manufacturer Part Number
AD9861
Description
Manufacturer
Analog Devices
Datasheet

Specifications of AD9861

Resolution (bits)
10bit
# Chan
2
Sample Rate
80MSPS
Interface
Par
Analog Input Type
Diff-Uni
Ain Range
2 V p-p
Adc Architecture
Pipelined
Pkg Type
CSP

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AD9861
Clock Input Configuration
The quality of the clock and data input signals is important in
achieving optimum performance. The external clock driver
circuitry provides the AD9861 with a low jitter clock input that
meets the min/max logic levels while providing fast edges.
When a driver is used to buffer the clock input, it should be
placed very close to the AD9861 clock input, thereby negating
any transmission line effects such as reflections due to
mismatch.
Programmable PLL
CLKIN can function either as an input data rate clock (PLL
enabled) or as a DAC data rate clock (PLL disabled).
The PLL clock multiplier and distribution circuitry produce the
necessary internal timing to synchronize the rising edge trig-
gered latches for the enabled interpolation filters and DACs.
This circuitry consists of a phase detector, charge pump, voltage
controlled oscillator (VCO), and clock distribution block, all
under SPI port control. The charge pump, phase detector, and
VCO are powered from PLL_AVDD, while the clock distribu-
tion circuits are powered from the DVDD supply.
To ensure optimum phase noise performance from the PLL
clock multiplier circuits, PLL_AVDD should originate from a
clean analog supply. The speed of the VCO within the PLL also
has an effect on phase noise.
The PLL locks with VCO speeds as low as 32 MHz up to
350 MHz, but optimal phase noise with respect to VCO speed is
achieved by running it in the range of 64 MHz to 200 MHz.
Power Dissipation
The AD9861 Tx path power is derived from three voltage
supplies: AVDD, DVDD, and DRVDD.
IDRVDD and IDVDD are very dependent on the input data
rate, the interpolation rate, and the activation of the internal
digital modulator. IAVDD has the same type of sensitivity to
data, interpolation rate, and the modulator function, but to a
much lesser degree (< 10%).
Sleep/Power-Down Modes
The AD9861 provides multiple methods for programming
power saving modes. The externally controlled TxPWRDWN
or SPI programmed sleep mode and full power-down mode are
the main options.
TxPWRDWN is used to disable all clocks and much of the
analog circuitry in the Tx path when asserted. In this mode, the
biases remain active, therefore reducing the time required for
re-enabling the Tx path. The time of recovery from power-
down for this mode is typically less than 10 µs.
Rev. 0 | Page 26 of 52
The sleep mode, when activated, turns off the DAC output
currents, but the rest of the chip remains functioning. When
coming out of sleep mode, the AD9861 immediately returns to
full operation.
A full power-down mode can be enabled through the SPI
register, which turns off all Tx path related analog and digital
circuitry in the AD9861. When returning from full power-down
mode, enough clock cycles must be allowed to flush the digital
filters of random data acquired during the power-down cycle.
Interpolation Stage
Interpolation filters are available for use in the AD9861 transmit
path, providing 1× (bypassed), 2×, or 4× interpolation.
The interpolation filters effectively increase the Tx data rate
while suppressing the original images. The interpolation filters
digitally shift the worst-case image further away from the
desired signal, thus reducing the requirements on the analog
output reconstruction filter.
There are two 2× interpolation filters available in the Tx path.
An interpolation rate of 4× is achieved using both interpolation
filters; an interpolation rate of 2× is achieved by enabling only
the first 2× interpolation filter.
The first interpolation filter provides 2× interpolation using a
39-tap filter. It suppresses out-of-band signals by 60 dB or more
and has a flat pass-band response (less than 0.1 dB ripple)
extending to 38% of the input Tx data rate (19% of the DAC
update rate, f
channel when using 2× interpolation.
The second interpolation filter provides an additional 2× interpola-
tion for an overall 4× interpolation. The second filter is a 15-tap
filter, which suppresses out-of-band signals by 60 dB or more.
The flat pass-band response (less than 0.1 dB attenuation) is
38% of the Tx input data rate (9.5% of f
input data rate per channel is 50 MSPS per channel when using
4× interpolation.
Latch/Demultiplexer
Data for the dual-channel Tx path can be latched in parallel
through two ports in half-duplex operations (HD20 mode) or
through a single port by interleaving the data (FD, HD10, and
Clone modes). See the Flexible I/O Interface Options section in
the Digital Block description and the Clock Distribution Block
section for further descriptions of each mode.
DAC
). The maximum input data rate is 80 MSPS per
DAC
). The maximum

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