EVAL-AD9837SDZ Analog Devices Inc, EVAL-AD9837SDZ Datasheet - Page 16

• Manufacturer Part Number: EVAL-AD9837SDZ
• Description: EVALUATION BOARD
• Manufacturer: Analog Devices Inc
• Series: -r

Specifications of EVAL-AD9837SDZ

• Main Purpose: Timing, Direct Digital Synthesis (DDS)
• Embedded: No
• Utilized Ic / Part: AD9837
• Primary Attributes: -
• Secondary Attributes: Graphical User Interface
• Kit Application Type: Clock & Timing
• Application Sub Type: Clock Generator
• Kit Contents: Software CD, USB Cable
• Silicon Manufacturer: Analog Devices
• Silicon Core Number: AD9837
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

AD9837
RESET FUNCTION
The reset function resets the appropriate internal registers to 0
to provide an analog output of midscale. A reset does not reset
the phase, frequency, or control registers. When the AD9837 is
powered up, the part should be reset (see the Powering Up the
AD9837 section). To reset the AD9837, set the RESET bit to 1.
To take the part out of reset, set the bit to 0. A signal appears at
the DAC output seven or eight MCLK cycles after the RESET
bit is set to 0.
Table 14. Applying the Reset Function
RESET Bit
0
1
SLEEP FUNCTION
Sections of the AD9837 that are not in use can be powered
down to minimize power consumption by using the sleep
function. The parts of the chip that can be powered down are
the internal clock and the DAC. The bits required for the sleep
function are shown in Table 15.
Table 15. Applying the Sleep Function
SLEEP1 Bit
0
0
1
1
DAC Powered Down
When the AD9837 is used to output the MSB of the DAC data
only, the DAC is not required. The DAC can be powered down
using the SLEEP12 bit to reduce power consumption.
Internal Clock Disabled
When the internal clock of the AD9837 is disabled, the DAC
output remains at its present value because the NCO is no
longer accumulating. New frequency, phase, and control words
can be written to the part when the SLEEP1 control bit is active.
Because the synchronizing clock (FSYNC) remains active, the
selected frequency and phase registers can also be changed using
the control bits. Setting the SLEEP1 bit to 0 enables the MCLK.
Any changes made to the registers while SLEEP1 was active are
observed at the output after a latency period (see the Latency
Period section).
VOUT PIN
The AD9837 offers a variety of outputs from the chip, all of
which are available from the VOUT pin. The available outputs
are the MSB of the DAC data, a sinusoidal output, or a triangle
output.
Result
No reset applied
Internal registers reset
SLEEP12 Bit
0
1
0
1
Result
No power-down
DAC powered down
Internal clock disabled
DAC powered down and
internal clock disabled
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The OPBITEN and MODE bits (Bit D5 and Bit D1 in the
control register) are used to determine the output that is
available from the AD9837 (see Table 16).
Table 16. Outputs from the VOUT Pin
OPBITEN Bit
0
0
1
1
1
MSB of the DAC Data
The MSB of the DAC data can be output from the AD9837. By
setting the OPBITEN bit (Bit D5) to 1, the MSB of the DAC data
is available at the VOUT pin. This is useful as a coarse clock
source. This square wave can also be divided by 2 before being
output. The DIV2 bit (Bit D3) in the control register controls
the frequency of this output from the VOUT pin.
Sinusoidal Output
The SIN ROM converts the phase information from the frequency
and phase registers into amplitude information, resulting in a
sinusoidal signal at the output. To obtain a sinusoidal output
from the VOUT pin, set the MODE bit (Bit D1) to 0 and the
OPBITEN bit (Bit D5) to 0.
Triangle Output
The SIN ROM can be bypassed so that the truncated digital output
from the NCO is sent to the DAC. In this case, the output is no
longer sinusoidal. The DAC produces a 10-bit linear triangular
function (see Figure 21). To obtain a triangle output from the
VOUT pin, set the MODE bit (Bit D1) to 1 and the OPBITEN
bit (Bit D5) to 0.
V
POWERING UP THE AD9837
The flowchart in Figure 22 shows the operating routine for the
AD9837. When the AD9837 is powered up, the part should be
reset. This resets the appropriate internal registers to 0 to provide
an analog output of midscale. To avoid spurious DAC outputs
during AD9837 initialization, the RESET bit should be set to 1
until the part is ready to begin generating an output.
A reset does not reset the phase, frequency, or control registers.
These registers will contain invalid data and, therefore, should
be set to known values by the user. The RESET bit should then
be set to 0 to begin generating an output. The data appears on
the DAC output seven or eight MCLK cycles after the RESET
bit is set to 0.
OUT MIN
V
OUT MAX
MODE Bit
0
1
0
0
1
Figure 21. Triangle Output
2π
DIV2 Bit
X
X
0
1
X
VOUT Pin Output
Sinusoid
Triangle
DAC data MSB/2
DAC data MSB
Reserved
4π
6π