AD9142BCPZ datasheet(26/65 Pages) AD

26 / 65 page

AD9142

Data Sheet

Rev. 0 | Page 26 of 64

DIGITAL DATAPATH

Figure 38. Block Diagram of Digital Datapath

The block diagram in Figure 38 shows the functionality of the

digital datapath. The digital processing includes

•

An input power detection block

•

Three half-band interpolation filters

•

A quadrature modulator consisting of a fine resolution

NCO and an fS/4 coarse modulation block

•

An inverse sinc filter

•

A gain and phase and offset adjustment block

The interpolation filters accept I and Q data streams and

process them as two independent data streams, whereas the

quadrature modulator and phase adjustment block accepts I

and Q data streams as a quadrature data stream. Therefore,

quadrature input data is required when digital modulation and

phase adjustment functions are used.

INTERPOLATION FILTERS

The transmit path contains three interpolation filters. Each of

the three interpolation filters provides a 2× increase in output data

rate and a low-pass function. The half-band (HB) filters are cas-

caded to provide 4× or 8× interpolation ratios.

The AD9142 provides three interpolation modes (see Table 6).

Each mode offers a different usable signal bandwidth in an

operating mode. Which mode to select depends on the required

signal bandwidth and the DAC update rate. Refer to Table 6 for

the maximum speed and signal bandwidth of each interpolation

mode.

The usable bandwidth is defined as the frequency band over

which the filters have a pass-band ripple of less than ±0.001 dB

and a stop band rejection of greater than 85 dB.

2× Interpolation Mode

Figure 39 and Figure 40 show the pass-band and all-band filter

response for 2× mode. Note that the transition from the

transition band to the stop band is much sharper than the tran-

sition from the pass band to the transition band. Therefore, when

the desired output signal moves out of the defined pass band,

the signal image, which is supposed to be suppressed by the stop

band, grows faster than the droop of the signal itself due to the

degraded pass-band flatness. In cases where the degraded image

rejection is acceptable or can be compensated by the analog

low-pass filter at the DAC output, it is possible to let the output

signal extend beyond the specified usable signal bandwidth.

Figure 39. Pass-Band Detail of 2× Mode

Figure 40. All-Band Response of 2× Mode

INPUT

POWER

DETECTION

AND

PROTECTION

HB1

HB2

HB3

INV

SINC

DIGITAL GAIN

AND PHASE

AND OFFSET

ADJUSTMENT

COARSE AND

FINE

MODULATION

0.02

–0.10

–0.08

–0.06

–0.04

–0.02

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

FREQUENCY (Hz)

–100

–90

–80

–70

–60

–50

–40

–30

–20

–10

0.4

0.2

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

FREQUENCY (Hz)

AD9142BCPZ Datasheet(PDF) 26 Page - Analog Devices

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