Datasheet

0.001
0.0008
0.0006
0.0004
0.0002
0
-0.0002
-0.0004
-0.0006
-0.0008
-0.001
0 100 200 300
Frequency(kHz)
400 500
Magnitude(dB)
600
f =20
CLK
MHz
20
0
-20
-40
-60
-80
-100
-120
-140
0 10 20 30 40 50
Frequency(MHz)
Magnitude(dB)
60
f =20
CLK
MHz
0.5
0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
400 450 500 550 600
Frequency(kHz)
Magnitude(dB)
650
f =20
CLK
MHz
R
BIAS
RBIAS
AGND
ADS1601
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 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 R
BIAS
changes
internally-generated voltages, including the internal
reference; therefore, it should be understood that the
recommendations of Table 3 are for external
Figure 47. Passband Transition
reference only.
ANTI-ALIAS REQUIREMENTS
Higher frequency, out-of-band signals must be
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 (f
CLK
= 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 R
BIAS
Resistor Values for
Different CLK Frequencies
TYPICAL POWER
DATA DISSIPATION
f
CLK
RATE R
BIAS
WITH REFEN HIGH
5MHz 315kSPS 267k 100mW
10MHz 625kSPS 210k 145mW
15MHz 940kSPS 140k 200mW
20MHz 1.25MSPS 60k 325mW
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