AD9773-EB datasheet(33/60 Pages) AD

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AD9773

Rev. D | Page 33 of 60

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.

tOD

tIQS

tIQH

tOD = 4.0ns (MIN)

TO 5.5ns (MAX)

tS = 3.0ns (MAX)

tH = –1.0ns (MAX)

tIQS = 3.5ns (MAX)

tIQH = –1.5ns (MAX)

CLKIN

IQSEL

ONEPORTCLK

I AND Q INTERLEAVED

INPUT DATA AT PORT 1

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.

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

e–jωt/2

COSINE

SINE

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.

SINUSOIDAL

MODULATION

COSINUSOIDAL

MODULATION

Ae–jωt/2j

Ae–jωt/2

Figure 58. Baseband Signal, Amplitude Modulated

with Sine and Cosine Carriers

AD9773-EB Datasheet(PDF) 33 Page - Analog Devices

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