Datasheet

0.001
0.0008
0.0006
0.0004
0.0002
0
-0.0002
-0.0004
-0.0006
-0.0008
-0.001
0 200 400 600
Frequency(kHz)
800 1000
Magnitude(dB)
1200
f =40MHz
CLK
20
0
-20
-40
-60
-80
-100
-120
-140
0 20 40 60 80 100
Frequency(MHz)
Magnitude(dB)
120
f =40MHz
CLK
0.5
0
-0.5
-1
-1.5
-2
-2.5
-3
-3.5
800 900 1000 1100 1200
Frequency(kHz)
Magnitude(dB)
1300
f =40MHz
CLK
R
BIAS
RBIAS
AGND
ADS1602
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 R
BIAS
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 R
BIAS
because
this interferes with the internal circuitry used to set
the biasing. Please note that changing the R
BIAS
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 be
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 (f
CLK
= 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 R
BIAS
Resistor Values for
Different CLK Frequencies
TYPICAL POWER
DATA DISSIPATION
f
CLK
RATE R
BIAS
WITH REFEN HIGH
16MHz 1MSPS 140kΩ 200mW
24MHz 1.5MSPS 100kΩ 270mW
32MHz 2MSPS 60kΩ 390mW
40MHz 2.5MSPS 37kΩ 530mW
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