ADS1601IPFBR datasheet(20/31 Pages) TI2

20 / 31 page

0.001

0.0008

0.0006

0.0004

0.0002

0.0004

0.0006

0.0008

0.001

100

200

300

Frequency(kHz)

400

500

600

=20

CLK

MHz

100

120

140

Frequency(MHz)

=20

CLK

MHz

0.5

1.0

1.5

2.0

2.5

3.0

3.5

400

450

500

550

600

Frequency(kHz)

650

=20

CLK

MHz

BIAS

RBIAS

AGND

ADS1601

SBAS322D

– DECEMBER 2004 – REVISED OCTOBER 2011

www.ti.com

Figure 46. Passband Ripple

Figure 48. 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 49. 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 RBIAS changes

internally-generated voltages, including the internal

reference; therefore, it should be understood that the

recommendations

Table

are

for

external

Figure 47. Passband Transition

reference only.

ANTI-ALIAS REQUIREMENTS

Higher

frequency,

out-of-band

signals

must

eliminated to prevent aliasing with ADCs. Fortunately,

the ADS1601 on-chip digital filter greatly simplifies

this filtering requirement. Figure 48 shows the

ADS1601 response out to 60MHz (fCLK = 20MHz).

Since the stop band extends out to 19.3MHz, the

anti-alias filter in front of the ADS1601 only needs to

Figure 49. 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

5MHz

315kSPS

267k

100mW

10MHz

625kSPS

210k

145mW

15MHz

940kSPS

140k

200mW

20MHz

1.25MSPS

60k

325mW

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