AD73411BBZ-80 Analog Devices Inc, AD73411BBZ-80 Datasheet - Page 32

• Manufacturer Part Number: AD73411BBZ-80
• Manufacturer: Analog Devices Inc

Specifications of AD73411BBZ-80

• Single Supply Voltage (typ): 3.3V
• Single Supply Voltage (min): 3V
• Single Supply Voltage (max): 3.6V
• Package Type: BGA
• Lead Free Status / RoHS Status: Compliant

AD73411
Analog Inputs
The analog input (encoder) section of the AD73411 can be inter-
faced to external circuitry in either ac-coupled or dc-coupled modes.
It is also possible to drive the ADC in either differential or
single-ended modes. If the single-ended mode is chosen it is
possible, using software control, to multiplex between two single-
ended inputs connected to the positive and negative input pins.
The primary concerns in interfacing to the ADC are to provide
adequate antialias filtering and to ensure that the signal source
will drive the switched-capacitor input of the ADC correctly.
The sigma-delta design of the ADC and its oversampling char-
acteristics simplify the antialias requirements, but it must be
remembered that the single-pole RC filter is primarily intended
to eliminate aliasing of frequencies above the Nyquist frequency of
the sigma-delta modulator’s sampling rate (typically 2.048 MHz).
It may still require a more specific digital filter implementa-
tion in the DSP to provide the final signal frequency response
characteristics. It is recommended that for optimum performance
the capacitors used for the antialiasing filter be of high quality
dielectric (NPO). The second issue mentioned above is interfacing
the signal source to the ADC’s switched capacitor input load.
The SC input presents a complex dynamic load to a signal
source, therefore, it is important to understand that the slew
rate characteristic is an important consideration when choosing
external buffers for use with the AD73411.
The AD73411’s on-chip 38 dB preamplifier can be enabled
when there is not enough gain in the input circuit; the preampli-
fier is configured by bits IGS0–2 of CRD. The total gain must be
configured to ensure that a full-scale input signal produces a signal
level at the input to the sigma-delta modulator of the ADC that
does not exceed the maximum input range.
The dc biasing of the analog input signal is accomplished with
an on-chip voltage reference. If the input signal is not biased at
the internal reference level (via REFOUT), it must be ac-coupled
with external coupling capacitors. C
The dc biasing of the input can then be accomplished using
resistors to REFOUT as in Figures 27 through 29.
0.047 F
ANTIALIAS
0.047 F
FILTER
100
100
0.1 F
REFOUT
REFCAP
VOUTP
VOUTN
VINP
VINN
+6/–15dB
PGA
REFERENCE
IN
CONTINUOUS
should be 0.1 µF or larger.
LOW-PASS
FILTER
TIME
AD73411
V
REF
0/38dB
PGA
The AD73411’s ADC inputs are biased about the internal refer-
ence level (REFCAP level), therefore, it may be necessary to bias
external signals to this level using the buffered REFOUT level
as the reference. This is applicable in either dc- or ac-coupled
configurations. In the case of dc coupling, the signal (biased
to REFOUT) may be applied directly to the inputs as shown in
Figure 25, or it may be conditioned in an external op amp where
it can also be biased to the reference level using the buffered
REFOUT signal as shown in Figure 26.
In the case of ac-coupling, a capacitor is used to couple the
signal to the input of the ADC. The ADC input must be biased
to the internal reference (REFCAP) level, which is done by
connecting the input to the REFOUT pin through a 10 kΩ
resistor as shown in Figure 27.
If the ADC is being connected in single-ended mode, the
AD73411 should be programmed for single-ended mode using
the SEEN and INV bits of CRF, and the inputs connected as
shown in Figure 28. When operated in single-ended input mode,
the AD73411 can multiplex one of the two inputs to the ADC
input, as shown in Figures 28 and 29.
0.1 F
10k
0.1 F
OPTIONAL
BUFFER
100
100
10k
0.047 F
0.047 F
REFCAP
0.1 F
REFOUT
VOUTP
VOUTN
0.1 F
VINN
REFOUT
REFCAP
VINP
VOUTP
VOUTN
VINP
VINN
+6/–15dB
+6/–15dB
PGA
PGA
REFERENCE
REFERENCE
CONTINUOUS
LOW-PASS
FILTER
CONTINUOUS
TIME
LOW-PASS
FILTER
TIME
AD73411
V
AD73411
REF
V
REF
0/38dB
PGA
0/38dB
PGA