AD9832BRU Analog Devices Inc, AD9832BRU Datasheet - Page 13

• Manufacturer Part Number: AD9832BRU
• Description: D/A Converter (D-A) IC
• Manufacturer: Analog Devices Inc

Specifications of AD9832BRU

• No. Of Pins: 16
• Peak Reflow Compatible (260 C): No
• No. Of Bits: 10 Bit
• Leaded Process Compatible: No
• Mounting Type: Surface Mount
• Interface Type: Serial
• Package / Case: 16-TSSOP
• Rohs Status: RoHS non-compliant
• Resolution (bits): 10 b
• Master Fclk: 25MHz
• Tuning Word Width (bits): 32 b
• Voltage - Supply: 2.97 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With: EVAL-AD9832EBZ - BOARD EVAL FOR AD9832
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

CIRCUIT DESCRIPTION
The AD9832 provides an exciting new level of integration
for the RF/communications system designer. The AD9832
combines the numerical controlled oscillator (NCO), a sine
look-up table, frequency and phase modulators, and a DAC
on a single integrated circuit.
The internal circuitry of the AD9832 consists of three main
sections. They are:
•
•
•
The AD9832 is a fully integrated direct digital synthesis (DDS)
chip. The chip requires a reference clock, a low precision resistor,
and eight decoupling capacitors to provide digitally created sine
waves up to 12.5 MHz. In addition to the generation of this RF
signal, the chip is fully capable of a broad range of simple and
complex modulation schemes. These modulation schemes are
fully implemented in the digital domain, allowing accurate and
simple realization of complex modulation algorithms using DSP
techniques.
NUMERICAL CONTROLLED OSCILLATOR AND
PHASE MODULATOR
The NCO and phase modulator consists of two frequency select
registers, a phase accumulator, and four phase offset registers.
The main component of the NCO is a 32-bit phase accumulator
that assembles the phase component of the output signal. Continuous
time signals have a phase range of 0 to 2 π. Outside this range of
numbers, the sinusoid functions repeat themselves in a periodic
manner. The digital implementation is no different. The accumulator
simply scales the range of phase numbers into a multibit digital
word. The phase accumulator in the AD9832 is implemented
with 32 bits. Therefore, in the AD9832, 2π = 2
ΔPhase term is scaled into this range of numbers 0 < ΔPhase <
2
where 0 < ΔPhase < 2
32
− 1.
Numerical controlled oscillator (NCO) and phase modulator
Sine look-up table
DAC
f = ΔPhase × f
MCLK
32
/2
.
32
32
. Likewise, the
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The input to the phase accumulator (that is, the phase step) can
be selected from either the FREQ0 register or the FREQ1 register
and can be controlled by the FSELECT pin or the FSELECT bit.
NCOs inherently generate continuous phase signals, thus
avoiding any output discontinuity when switching between
frequencies.
Following the NCO, a phase offset can be added to perform
phase modulation using the 12-bit PHASEx registers. The contents
of these registers are added to the most significant bits of the NCO.
The AD9832 has four PHASEx registers, the resolution of these
registers being 2 π/4096.
SINE LOOK-UP TABLE (LUT)
To make the output useful, the signal must be converted from
phase information into a sinusoidal value. Because phase information
maps directly into amplitude, a ROM LUT converts the phase
information into amplitude. To do this, the digital phase
information is used to address a sine ROM LUT. Although the
NCO contains a 32-bit phase accumulator, the output of the
NCO is truncated to 12 bits. Using the full resolution of the phase
accumulator is impractical and unnecessary because this would
require a look-up table of 2
It is only necessary to have sufficient phase resolution in the
LUTs so that the dc error of the output waveform is dominated
by the quantization error in the DAC. This requires the look-up
table to have two more bits of phase resolution than the 10-bit DAC.
DIGITAL-TO-ANALOG CONVERTER
The AD9832 includes a high impedance current source 10-bit
DAC, capable of driving a wide range of loads at different speeds.
Full-scale output current can be adjusted for optimum power
and external load requirements by using a single external
resistor (R
The DAC is configured for single-ended operation. The load
resistor can be any value required, as long as the full-scale
voltage developed across it does not exceed the voltage compliance
range. Because full-scale current is controlled by R
to R
if the DAC full-scale output current is significantly less than 4 mA,
the linearity of the DAC may degrade.
SET
can balance changes made to the load resistor. However,
SET
).
32
entries.
SET
, adjustments
AD9832