AD9148BPCZ datasheet(51/73 Pages) AD

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Preliminary Technical Data

AD9148

Rev. PrA | Page 51 of 73

Table 17. Programmable Inverse Sinc Filter Coefficient Widths and Ranges

Coefficient

Width

Minimum

Maximum

c0 in-phase (real)

100b

011b

−4

c0 quadrature (imaginary)

0100b

011b

−4

c1 in-phase (real)

1000b

0111b

−8

c1 quadrature (imaginary)

1000b

0111b

−8

c2 in-phase (real)

10000b

01111b

−16

c2 quadrature (imaginary)

10000b

01111b

−16

c3 in-phase (real)

1000000b

0111111b

−64

c3 quadrature (imaginary)

1000000b

0111111b

−64

c4 in-phase (real)

1000000000b

0111111111b

−1024

1023

c4 quadrature (imaginary)

1000000000b

0111111111b

−1024

1023

The real and imaginary filters are implemented using the

structure described in Figure 61 and Figure 62.

INPUTn

OUTPUTn

z–1

c0REAL

c1REAL

c2REAL

c3REAL

c4REAL

c5REAL

Figure 61. Real Filter implementation

INPUTn

OUTPUTn

z–1

–

c0IMG

c1IMG

c2IMG

c3IMG

c4IMG

c5IMG

–

Figure 62. Imaginary Filter implementation

The AD9148 evaluation tools provide software that allow for

the processing of the filter coefficients based on the DAC

sampling frequency, the amount of interpolation used

(combination of HB1, HB2 and HB3), and the desired center

frequency. This center frequency is limited to

[−(fDAC/2, fDAC/2/INT); fDAC/2, fDAC/2/INT]

where

INT is the interpolation rate.

When there is no interpolation used, the real filter coefficients

can be fixed at (no imaginary coefficients):

C0 = 2

;

C8 = 2

C1 = −4

;

C7 = −4

C2 = 10

;

C6 = 10

C3 = −35

;

C5 = −35

C4 = 401

INTERPOLATION FILTERS

The transmit path contains three interpolation filters. Each of

the three interpolation filters provides a 2× increase in output

data rate. The filters can be cascaded to provide 2×, 4×, or 8×

interpolation ratios. Each of the half-band filter stages offers a

different combination of bandwidths and operating modes.

The bandwidth of the three 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

•

Bandwidth of HB3 = 0.4 × fIN3

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 is discussed 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 and HB3 filters each have eight modes of operation.

AD9148BPCZ Datasheet(PDF) 51 Page - Analog Devices

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