AD9775EB AD [Analog Devices], AD9775EB Datasheet - Page 25

• Manufacturer Part Number: AD9775EB
• Description: 14-Bit, 160 MSPS 2X/4X/8X Interpolating Dual TxDAC+ D/A Converter
• Manufacturer: AD [Analog Devices]

The programmable modes’ ONEPORTCLK inversion,
ONEPORTCLK driver strength, and IQ pairing described in
the previous section (PLL Enabled, One Port Mode) have
identical functionality with the PLL disabled.
DIGITAL FILTER MODES
The I and Q data paths of the AD9775 have their own indepen-
dent half-band FIR filters. Each data path consists of three FIR
filters, providing up to 8× interpolation for each channel. The
rate of interpolation is determined by the state of Control Register
01h, Bits 7 and 6. Figures 1a–1c show the response of the digi-
tal filters when the AD9775 is set to 2×, 4×, and 8× modes. The
frequency axes of these graphs have been normalized to the input
data rate of the DAC. As the graphs show, the digital filters can
provide greater than 75 dB of out-of-band rejection.
An online tool is available for quick and easy analysis of the
AD9775 interpolation filters in the various modes. The link
can be accessed at:
interactiveTools/dac/ad9777image.html.
REV. 0
t
t
t
t
t
(TYP SPECS)
INPUT DATA AT PORT 1
OD
S
H
IQS
IQH
I AND Q INTERLEAVED
= 3.0ns
= –1.0ns
= 4.7ns
Figure 22. Timing Requirements in One Port
Input Mode with PLL Disabled
= 3.5ns
= –1.5ns
ONEPORTCLK
CLKIN
IQSEL
www.analog.com/techSupport/designTools/
t
IQS
t
OD
t
S
t
H
t
IQH
–25–
AMPLITUDE MODULATION
Given two sine waves at the same frequency, but with a 90 phase
difference, a point of view in time can be taken such that the
waveform that leads in phase is cosinusoidal and the waveform
that lags is sinusoidal. Analysis of complex variables states that
the cosine waveform can be defined as having real positive and
negative frequency components, while the sine waveform consists
of imaginary positive and negative frequency images. This is
shown graphically in the frequency domain in Figure 23.
Amplitude modulating a baseband signal with a sine or a cosine
convolves the baseband signal with the modulating carrier in the
frequency domain. Amplitude scaling of the modulated signal
reduces the positive and negative frequency images by a factor of
two. This scaling will be very important in the discussion of the
various modulation modes. The phase relationship of the modu-
lated signals is dependent on whether the modulating carrier is
sinusoidal or cosinusoidal, again with respect to the reference
point of the viewer. Examples of sine and cosine modulation are
given in Figure 24.
Figure 23. Real and Imaginary Components of
Sinusoidal and Cosinusoidal Waveforms
Figure 24. Baseband Signal, Amplitude
Modulated with Sine and Cosine Carriers
Ae
Ae
–j t
–j t
/2j
/2
e
e
–j t
–j t
/2j
/2
DC
DC
DC
DC
Ae
Ae
–j t
–j t
/2j
e
e
/2
–j t
–j t
COSINE
SINE
COSINUSOIDAL
SINUSOIDAL
MODULATION
MODULATION
/2j
/2
AD9775