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AD9146

Rev. 0 | Page 31 of 52

DIGITAL DATAPATH

The block diagram in Figure 39 shows the functionality of the

digital datapath. The digital processing includes a premodula-

tion block, two half-band (HB) interpolation filters, phase and

offset adjustment blocks, and an inverse sinc filter.

PREMOD

PHASE

AND

OFFSET

ADJUSTMENT

HB1

HB2

SINC–1

Figure 39. Block Diagram of Digital Datapath

The digital datapath accepts I and Q data streams and processes

them as a quadrature data stream. The signal processing blocks can

be used when the input data stream is represented as complex data.

The digital datapath can also be used to process an input data

stream representing two independent real data streams, but the

functionality is somewhat restricted. The premodulation block

and any of the nonshifted interpolation filter modes can be used

for an input data stream representing two independent real data

streams. See the Coarse Modulation Mixing Sequences section

for more information.

PREMODULATION

The half-band interpolation filters have selectable pass bands

that allow the center frequencies to be moved in increments of

one-half their input data rate. The premodulation block provides

a digital upconversion of the incoming waveform by one-half the

incoming data rate, fDATA. This can be used to frequency-shift base-

band input data to the center of the interpolation filter pass band.

INTERPOLATION FILTERS

The transmit path contains two interpolation filters. Both inter-

polation filters provide a 2× increase in output data rate. The

half-band (HB) filters can be individually bypassed or cascaded

to provide 1×, 2×, or 4× interpolation ratios. Each half-band

filter stage offers a different combination of bandwidths and

operating modes.

The bandwidth of the two half-band filters with respect to the

data rate at the filter input is as follows:

•

Bandwidth of HB1 = 0.8 × fIN1

•

Bandwidth of HB2 = 0.5 × fIN2

The usable bandwidth is defined as the frequency over which

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

an image rejection of greater than +85 dB. As described in the

Half-Band Filter 1 (HB1) section, the image rejection usually

sets the usable bandwidth of the filter, not the pass-band

flatness.

The half-band filters operate in several modes, providing

programmable pass-band center frequencies as well as signal

modulation. The HB1 filter has four modes of operation, and

the HB2 filter has eight modes of operation.

Half-Band Filter 1 (HB1)

HB1 has four modes of operation, as shown in Figure 40. The

shape of the filter response is identical in each of the four modes.

The four modes are distinguished by two factors: the filter center

frequency and whether the input signal is modulated by the

filter.

–20

–40

–60

–80

–100

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

FREQUENCY (×

fIN1) (Hz)

MODE 0

MODE 1

MODE 3

MODE 2

Figure 40. HB1 Filter Modes

As shown in Figure 40, the center frequency in each mode is

offset by one-half the input data rate (fIN1) of the filter. Mode 0

and Mode 1 do not modulate the input signal. Mode 2 and

Mode 3 modulate the input signal by fIN1. When operating in

Mode 0 and Mode 2, the I and Q paths operate independently

and no mixing of the data between channels occurs. When oper-

ating in Mode 1 and Mode 3, mixing of the data between the

I and Q paths occurs; therefore, the data input into the filter is

assumed to be complex. Table 15 summarizes the HB1 modes.

Table 15. HB1 Filter Modes

Mode

fCENTER

fMOD

Input Data

None

Real or complex

fIN/2

None

Complex

fIN

Real or complex

3fIN/2

fIN

Complex

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