AD9775EB datasheet(25/48 Pages) AD

25 / 48 page

REV. 0

AD9775

–25–

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.

tOD

CLKIN

I AND Q INTERLEAVED

INPUT DATA AT PORT 1

ONEPORTCLK

IQSEL

tIQH

tIQS

tOD = 4.7ns

tS = 3.0ns

tH = –1.0ns

tIQS = 3.5ns

tIQH = –1.5ns

(TYP SPECS)

Figure 22. Timing Requirements in One Port

Input Mode with 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: www.analog.com/techSupport/designTools/

interactiveTools/dac/ad9777image.html.

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.

e–j t/2j

COSINE

SINE

e–j t/2

e–j t/2j

e–j t/2

Figure 23. 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

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.

SINUSOIDAL

MODULATION

Ae–j t/2j

Ae–j t/2

Ae–j t/2j

COSINUSOIDAL

MODULATION

Figure 24. Baseband Signal, Amplitude

Modulated with Sine and Cosine Carriers

AD9775EB датащи(PDF) 25 Page - Analog Devices

AD9775EB датащи(HTML) 25 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

датащи скачать

ссылки URL