ADAU1401AWBSTZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'ADAU1401AWBSTZ' PDF : 52 Pages View PDF
ADAU1401A
AUDIO ADCs
The ADAU1401A has two Σ-Δ ADCs. The signal-to-noise ratio
(SNR) of the ADCs is 100 dB, and the THD + N is −83 dB.
The stereo audio ADCs are current input; therefore, a voltage-
to-current resistor is required on the inputs. This means that
the voltage level of the input signals to the system can be set to
any level; only the input resistors need to be scaled to provide
the proper full-scale current input. The ADC0 and ADC1 input
pins, as well as the ADC_RES pin, have an internal 2 kΩ resistor
for ESD protection. The voltage seen directly on the ADC input
pins is the 1.5 V common-mode voltage.
The external resistor connected to ADC_RES sets the full-scale
current input of the ADCs. The full range of the ADC inputs is
100 μA rms with an external 18 kΩ resistor on ADC_RES (20 kΩ
total, because it is in series with the internal 2 kΩ). The only
reason to change the ADC_RES resistor is if a sampling rate
other than 48 kHz is used.
The voltage-to-current resistors connected to ADC0 and ADC1 set
the full-scale voltage input of the ADCs. With a full-scale current
input of 100 μA rms, a 2.0 V rms signal with an external 18 kΩ
resistor (in series with the 2 kΩ internal resistor) results in an
input using the full range of the ADC. The matching of these
resistors to the ADC_RES resistor is important to the operation of
the ADCs. For these three resistors, a 1% tolerance is recommended.
The ADC0 input pin and/or the ADC1 input pin can be left
unconnected if the corresponding channel of the ADC is unused.
The calculations of resistor values assume a 48 kHz sample rate.
The recommended input and current setting resistors scale linearly
with the sample rate because the ADCs have a switched-capacitor
input. The total value (2 kΩ internal plus external resistor) of the
ADC_RES resistor with sample rate fS_NEW can be calculated as
follows:
RTOTAL
= 20
kΩ ×
48,000
f S _ NEW
The values of the resistors (internal plus external) in series with
the ADC0 and ADC1 pins can be calculated as follows:
R INPUT TOTAL
= (rms
Input
Voltage) × 10
kΩ ×
48,000
f S _ NEW
Table 14 lists the external and total resistor values for common
signal input levels at a 48 kHz sampling rate. A full-scale rms
input voltage of 0.9 V is shown in the table because a full-scale
signal at this input level is equal to a full-scale output on the DACs.
Table 14. ADC Input Resistor Values
Full-Scale
RMS Input
Voltage (V)
0.9
1.0
2.0
ADC_RES
Value (kΩ)
18
18
18
ADC0/ADC1
Resistor
Value (kΩ)
7
8
18
Total ADC0/ADC1
Input Resistance
(External +
Internal) (kΩ)
9
10
20
Figure 17 shows a typical configuration of the ADC inputs for
a 2.0 V rms input signal for a fS of 48 kHz. The 47 μF capacitors are
used to ac-couple the signals so that the inputs are biased at 1.5 V.
47µF
ADAU1401A
18kΩ
ADC0
47µF
18kΩ
ADC1
18kΩ
ADC_RES
Figure 17. Audio ADC Input Configuration
Rev. A | Page 20 of 52
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