AD73311LAR-REEL Analog Devices Inc, AD73311LAR-REEL Datasheet - Page 23

• Manufacturer Part Number: AD73311LAR-REEL
• Description: IC ANALOG FRONT END 20-SOIC T/R
• Manufacturer: Analog Devices Inc

Specifications of AD73311LAR-REEL

• Rohs Status: RoHS non-compliant
• Number Of Bits: 16
• Number Of Channels: 2
• Power (watts): 50mW
• Voltage - Supply, Analog: 3V
• Voltage - Supply, Digital: 3V
• Package / Case: 20-SOIC (7.5mm Width)

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.
The AD73311L’s ADC inputs are biased about the internal
reference level (REFCAP level), therefore it may be neces-
sary 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
(using amplifier bypass), 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.
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
VINN
VINP
0.1 F
REFOUT
REFCAP
VOUTP
VOUTN
VINP
VINN
+6/–15dB
PGA
+6/15dB
IN
REFERENCE
PGA
should be 0.1 µF or larger.
REFERENCE
CONTINUOUS
LOW-PASS
FILTER
TIME
CONTINUOUS
LOW-PASS
FILTER
TIME
AD73311L
V
REF
AD73311L
V
0/38dB
REF
PGA
0/38dB
PGA
If the ADC is being connected in single-ended mode, the
AD73311L 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 AD73311L can multiplex one of the two inputs to the ADC
input, as shown in Figures 28 and 29.
Interfacing to an Electret Microphone
Figure 30 details an interface for an electret microphone which
may be used in some voice applications. Electret microphones
typically feature a FET amplifier whose output is accessed on
the same lead that supplies power to the microphone; therefore,
this output signal must be capacitively coupled to remove the
power supply (dc) component. In this circuit the AD73311L
input channel is being used in single-ended mode where the
internal inverting amplifier provides suitable gain to scale the
input signal relative to the ADC’s full-scale input range. The
buffered internal reference level at REFOUT is used via an
external buffer to provide power to the electret microphone.
This provides a quiet, stable supply for the microphone. If this
is not a concern, the microphone can be powered from the
system power supply.
10k
10k
0.1 F
0.1 F
100
100
0.047
0.047
F
F
REFOUT
REFOUT
0.1 F
REFCAP
REFCAP
0.1 F
VOUTP
VOUTN
VOUTP
VOUTN
VINN
VINN
VINP
VINP
+6/–15dB
+6/15dB
PGA
PGA
REFERENCE
REFERENCE
CONTINUOUS
CONTINUOUS
LOW-PASS
LOW-PASS
FILTER
FILTER
TIME
TIME
AD73311L
AD73311L
AD73311L
V
V
REF
REF
0/38dB
0/38dB
PGA
PGA