AD9773_15 Datasheet, PDF (33/60 Pages) Analog Devices – 12-Bit, 160 MSPS, 2/4/8 Interpolating

Under these conditions, IQSEL = 0 latches the data into the I
channel on the clock rising edge, while IQSEL = 1 latches the
data into the Q channel. It is possible to invert the I and Q
selection by setting Control Register 02h, Bit 1 to the invert
state (Logic 1). Figure 56 illustrates the timing requirements for
the data inputs as well as the IQSEL input. Note that the
1× interpolation rate is not available in the one-port mode.
One-port mode is very useful when interfacing with devices
such as the Analog Devices AD6622 or AD6623 transmit signal
processors, in which two digital data channels have been
interleaved (multiplexed).
The programmable modes’ ONEPORTCLK inversion,
ONEPORTCLK driver strength and IQ pairing described in the
PLL Enabled, Two-Port Mode section have identical
functionality with the PLL disabled.
t_OD
CLKIN
ONEPORTCLK
I AND Q INTERLEAVED
INPUT DATA AT PORT 1
t_S t_H
IQSEL
t_OD = 4.0ns (MIN)
TO 5.5ns (MAX)
t_S = 3.0ns (MAX)
t_H = –1.0ns (MAX)
t_IQS = 3.5ns (MAX)
t_IQH = –1.5ns (MAX)
t_IQS
t_IQH
Figure 56. Timing Requirements in One-Port
Input Mode with DLL Disabled
DIGITAL FILTER MODES
The I and Q data paths of the AD9773 have their own
independent 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. Figure 2 to Figure 4 show the
response of the digital filters when the AD9773 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
AD9773 interpolation filters in the various modes.
AD9773
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 57.
e^–jωt/2j
SINE
DC
e^–jωt/2j
e^–jωt/2
e^–jωt/2
COSINE
DC
Figure 57. Real and Imaginary Components of
Sinusoidal and Cosinusoidal Waveforms
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 2. This scaling is very important in the discussion of
the various modulation modes. The phase relationship of the
modulated 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 58.
Ae^–jωt/2j
SINUSOIDAL
MODULATION
DC
Ae^–jωt/2j
Ae^–jωt/2
Ae^–jωt/2
COSINUSOIDAL
MODULATION
DC
Figure 58. Baseband Signal, Amplitude Modulated
with Sine and Cosine Carriers
Rev. D | Page 33 of 60