ADS1602IPFBT datasheet(20/30 Pages) TI2

20 / 30 page

0.001

0.0008

0.0006

0.0004

0.0002

-0.0002

-0.0004

-0.0006

-0.0008

-0.001

200

400

600

Frequency(kHz)

800

1000

1200

=40MHz

CLK

-20

-40

-60

-80

-100

-120

-140

100

Frequency(MHz)

120

=40MHz

CLK

0.5

-0.5

-1

-1.5

-2

-2.5

-3

-3.5

800

900

1000

1100

1200

Frequency(kHz)

1300

=40MHz

CLK

BIAS

RBIAS

AGND

ADS1602

SBAS341E

– DECEMBER 2004 – REVISED OCTOBER 2011

www.ti.com

Figure 49. Passband Ripple

Figure 51. Frequency Response Out to 120MHz

ANALOG POWER DISSIPATION

An external resistor connected between the RBIAS

pin and the analog ground sets the analog current

level, as shown in Figure 52. The current is inversely

proportional to the resistor value. Table 3 shows the

recommended values of RBIAS for different CLK

frequencies. Notice that the analog current can be

reduced when using a slower frequency CLK input

because the modulator has more time to settle. Avoid

adding any capacitance in parallel to RBIAS because

this interferes with the internal circuitry used to set

the biasing. Please note that changing the RBIAS

resistor value changes all internally-generated bias

voltages, including the internal reference; therefore,

the recommendations in Table 3 are only for when

Figure 50. Passband Transition

using an external reference.

ANTIALIAS REQUIREMENTS

Higher

frequency,

out-of-band

signals

must

eliminated to prevent aliasing with ADCs. Fortunately,

the ADS1602 on-chip digital filter greatly simplifies

this filtering requirement. Figure 51 shows the

ADS1602 response out to 120MHz (fCLK = 40MHz).

Since the stop band extends out to 38.6MHz, the

antialias filter in front of the ADS1602 only needs to

Figure 52. External Resistor Used to Set Analog

be designed to remove higher frequency signals than

Power Dissipation

this, which can usually be accomplished with a simple

RC circuit on the input driver.

Table 3. Recommended RBIAS Resistor Values for

Different CLK Frequencies

TYPICAL POWER

DATA

DISSIPATION

fCLK

RATE

RBIAS

WITH REFEN HIGH

16MHz

1MSPS

140k

200mW

24MHz

1.5MSPS

100k

270mW

32MHz

2MSPS

60k

390mW

40MHz

2.5MSPS

37k

530mW

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