ADS1610IPAPR.B datasheet(17/29 Pages) TI2

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FREQUENCY RESPONSE

−1

−2

−3

−4

−5

−6

−7

4.0

4.2

4.1

4.3

4.5

4.7

4.9

4.4

Frequency (MHz)

4.6

4.8

5.0

−20

−40

−60

−80

−100

−120

Frequency (MHz)

−20

−40

−60

−80

−100

−120

Frequency (MHz)

180

100

120

140

160

0.00020

0.00015

0.00010

0.00005

−0.00005

−0.00010

−0.00015

−0.00020

0.5

1.0

Frequency (MHz)

1.5

2.0

2.5

3.0

3.5

4.0

4.5

ADS1610

SBAS344C – AUGUST 2005 – REVISED OCTOBER 2006

The linear phase FIR digital filter sets the overall

frequency response. The decimation rate is set to 6

(MODE = 00) for all the figures shown in this section.

Figure 34 shows the frequency response from DC to

30 MHz for fCLK = 60 MHz. The frequency response

of the ADS1610 filter scales directly with CLK

frequency. For example, if the CLK frequency is

decreased by half (to 30 MHz), the values on the

X-axis in Figure 34 would need to be scaled by half,

with the span becoming DC to 15MHz.

Figure 36. Passband Transition

The overall frequency response repeats at multiples

of the CLK frequency. To help illustrate this,

Figure 37 shows the response out to 180 MHz (fCLK =

60MHz). Notice how the passband response repeats

at 60MHz, 120MHz, and 180MHz; it is important to

consider this sequence when there is high-frequency

noise

present

with

the

signal.

The

modulator

bandwidth extends to 100MHz. High-frequency noise

around 60MHz and 120MHz will not be attenuated

by either the modulator or the digital filter. This noise

will alias back inband and reduce the overall SNR

performance unless it is filtered out prior to the

Figure 34. Frequency Response

ADS1610. To prevent this, place an anti-alias filter in

front of the ADS1610 that rolls off before 55MHz.

Figure 35 shows the passband ripple from DC to

4.4MHz (fCLK = 60MHz). Figure 36 shows a closer

view of the passband transition by plotting the

response from 4.0MHz to 5.0MHz (fCLK = 60MHz).

Figure 37. Frequency Response Out to 120MHz

Figure 35. Passband Ripple

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