AD9161BBCZ datasheet(66/144 Pages) AD

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AD9161/AD9162

Data Sheet

Rev. D | Page 66 of 66

The FIR85 filter can be used with the 1× bypass mode, but in

that mode, the signal is limited to the lower half of the Nyquist

zone, that is, up to fDAC/4. If the NCO is used with FIR85 in 1×

bypass mode, images of the NCO upconversion appears because

the data interface in 1× bypass is real; therefore, an image reject

upconversion cannot be accomplished by the NCO. To synthe-

size a signal and then upconvert it with the NCO, use the complex

data interface and choose an appropriate interpolator prior to

FIR85.

Table 35 shows how to select each available interpolation mode,

their usable bandwidths, and their maximum data rates. Calculate

the available signal bandwidth as the interpolator filter bandwidth,

BW, multiplied by fDAC/InterpolationFactor, as follows:

BWSIGNAL = BWFILT × (fDAC/InterpolationFactor)

Filter Performance

The interpolation filters interpolate between existing data in

such a way that they minimize changes in the incoming data

while suppressing the creation of interpolation images. This

datapath is shown for each filter in Figure 162.

The usable bandwidth (as shown in Table 35) is defined as the

frequency band over which the filters have a pass-band ripple of

less than ±0.001 dB and an image rejection of greater than

85 dB. A conceptual drawing that shows the relative bandwidth

of each of the filters is shown in Figure 162. The maximum pass

band amplitude of all filters is the same; they are different in the

illustration to improve understanding.

–1500

–500

500

1500

2500

FREQUENCY (MHz)

1×

2×

3×

4×

6×

8×

12×

16×

24×

FIR85

Figure 162. All Band Responses of Interpolation Filters

Filter Performance Beyond Specified Bandwidth

Some of the interpolation filters are specified to 0.4 × fDATA (with

a pass band). The filters can be used slightly beyond this ratio at

the expense of increased pass-band ripple and decreased

interpolation image rejection.

Table 35. Interpolation Modes and Usable Bandwidth

Interpolation Mode

INTERP_MODE, Register 0x110, Bits[3:0]

Available Signal Bandwidth

(BW)1

Maximum fDATA (MHz)

1× (Bypass)

0x00

fDAC/2

fDAC2

2×

0x01

BW × fDATA/2

fDAC/22

3×

0x02

BW × fDATA/2

fDAC/3

4×

0x03

BW × fDATA/2

fDAC/4

6×

0x04

BW × fDATA/2

fDAC/6

8×

0x05

BW × fDATA/2

fDAC/8

12×

0x06

BW × fDATA/2

fDAC/12

16×

0x07

BW × fDATA/2

fDAC/16

24×

0x08

BW × fDATA/2

fDAC/24

2× NRZ (Register 0x111, Bit 0 = 1)

Any combination3

0.45 × fDAC4

fDAC (real) or fDAC/2(complex)2

1 The data rate (fDATA) for all interpolator modes is a complex data rate, meaning each of I data and Q data run at that rate. The data rate for the 1× bypass mode is a real

data rate. Available signal bandwidth is the data rate multiplied by the bandwidth of the initial 2× or 3× interpolator filters, which can be set to BW = 80% or BW =

90%. This bandwidth is centered at 0 Hz.

2 The maximum speed for 1× and 2× interpolation is limited by the JESD204B interface, and is 5000 MHz (real) in 1× or 2500 MHz (complex) in 2× interpolation mode.

3 The 2× NRZ filter, FIR85, can be used with any of the interpolator combinations. When used in 1× bypass mode, the desired signal must be placed in the lower half of the

first Nyquist zone, as in 0 to DAC clock ÷ 4 MHz.

4 The bandwidth of the FIR85 filter is centered at 0 Hz.

AD9161BBCZ Datasheet(PDF) 66 Page - Analog Devices

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