AD6653-150EBZ Analog Devices Inc, AD6653-150EBZ Datasheet - Page 32

• Manufacturer Part Number: AD6653-150EBZ
• Manufacturer: Analog Devices Inc

Specifications of AD6653-150EBZ

• Lead Free Status / Rohs Status: Compliant

AD6653
NUMERICALLY CONTROLLED OSCILLATOR (NCO)
FREQUENCY TRANSLATION
This processing stage comprises a digital tuner consisting of
a 32-bit complex numerically controlled oscillator (NCO). The
two channels of the AD6653 share a single NCO. The NCO is
optional and can be bypassed by clearing Bit 0 of Register 0x11D.
This NCO block accepts a real input from the ADC stage and
outputs a frequency translated complex (I and Q) output.
The NCO frequency is programmed in Register 0x11E,
Register 0x11F, Register 0x120, and Register 0x121. These four
8-bit registers make up a 32-bit unsigned frequency programming
word. Frequencies between −CLK/2 and +CLK/2 are represented
using the following frequency words:
•
•
•
Use the following equation to calculate the NCO frequency:
where:
NCO_FREQ is a 32-bit twos complement number representing
the NCO frequency register.
f is the desired carrier frequency in hertz (Hz).
f
NCO SYNCHRONIZATION
The AD6653 NCOs within a single part or across multiple parts
can be synchronized using the external SYNC input. Bit 3 and
Bit 4 of Register 0x100 allow the NCO to be resynchronized on
every SYNC signal or only on the first SYNC signal after the
register is written. A valid SYNC causes the NCO to restart at
the programmed phase offset value.
CLK
is the AD6653 ADC clock rate in hertz (Hz).
0x8000 0000 represents a frequency given by −CLK/2.
0x0000 0000 represents dc (frequency = 0 Hz).
0x7FFF FFFF represents CLK/2 − CLK/2
NCO_FREQ
=
2
32
×
Mod
(
f
CLK
f
,
f
CLK
)
32
.
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PHASE OFFSET
The NCO phase offset register at Address 0x122 and
Address 0x123 adds a programmable offset to the phase
accumulator of the NCO. This 16-bit register is interpreted
as a 16-bit unsigned integer. A 0x00 in this register corresponds
to no offset, and a 0xFFFF corresponds to an offset of 359.995°.
Each bit represents a phase change of 0.005°. This register
allows multiple NCOs to be synchronized to produce outputs
with predictable phase differences. Use the following equation
to calculate the NCO phase offset value:
where:
NCO_PHASE is a decimal number equal to the 16-bit binary
number to be programmed at Register 0x122 and Register 0x123.
PHASE is the desired NCO phase in degrees.
NCO AMPLITUDE AND PHASE DITHER
The NCO block contains amplitude and phase dither to
improve the spurious performance. Amplitude dither improves
performance by randomizing the amplitude quantization errors
within the angular-to-Cartesian conversion of the NCO. This
option reduces spurs at the expense of a slightly raised noise
floor. With amplitude dither enabled, the NCO has an SNR of
>93 dB and an SFDR of >115 dB. With amplitude dither
disabled, the SNR is increased to >96 dB at the cost of SFDR
performance, which is reduced to 100 dB. The NCO amplitude
dither is recommended and is enabled by setting Bit 1 of
Register 0x11D.
NCO_PHASE = 2
16
× PHASE/360