AD73311LAR-REEL7 Analog Devices Inc, AD73311LAR-REEL7 Datasheet - Page 22

• Manufacturer Part Number: AD73311LAR-REEL7
• Description: IC ANALOG FRONT END 20-SOIC T/R
• Manufacturer: Analog Devices Inc

Specifications of AD73311LAR-REEL7

• 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)
• Single Supply Voltage (min): 2.7V
• Single Supply Voltage (max): 3.3V
• Package Type: SOIC W
• Lead Free Status / RoHS Status: Not Compliant

AD73311L
In the DAC section, increasing the sampling rate by interpola-
tion creates images of the original waveform at intervals of the
original sampling frequency. These images may be sufficiently
rejected by external circuitry, but the sinc-cubed filter in the
interpolator again nulls the output spectrum at integer intervals
of the original sampling rate which corresponds with the images
due to the interpolation process.
The spectral response of a sinc-cubed filter shows the character-
istic nulls at integer intervals of the sampling frequency. Its
passband characteristic (up to Nyquist frequency) features a
roll-off that continues up to the sampling frequency, where the
first null occurs. In many applications this smooth response will
not give sufficient attenuation of frequencies outside the band of
interest, therefore, it may be necessary to implement a final filter
in the DSP which will equalize the passband rolloff and provide
a sharper transition band and greater stopband attenuation.
–100
–100
–20
–40
–60
–80
–20
–40
–60
–80
20
20
0
0
0
0
1
1
2
2
FREQUENCY – Hz
FREQUENCY – Hz
3
3
4
4
5
5
6
6
10
10
7
7
4
4
DESIGN CONSIDERATIONS
The AD73311L features both differential inputs and outputs on
each channel to provide optimal performance and avoid common-
mode noise. It is also possible to interface either inputs or outputs
in single-ended mode. This section details the choice of input
and output configurations and also gives some tips towards
successful configuration of the analog interface sections.
Analog Inputs
The analog input (encoder) section of the AD73311L can be
interfaced to external circuitry in either ac-coupled or dc-coupled
modes.
It is also possible to drive the ADCs 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 firstly to
provide adequate antialias filtering and to ensure that the signal
source will drive the switched-capacitor input of the ADC cor-
rectly. The sigma-delta design of the ADC and its oversampling
characteristics 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 AD73311L. The internal inverting
op amps on the AD73311L are specifically designed to interface
to the ADC’s SC input stage.
The AD73311L’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.
0.047 F
ANTIALIAS
0.047 F
FILTER
100
100
0.1 F
REFOUT
REFCAP
VOUTP
VOUTN
VINN
VINP
+6/–15dB
PGA
REFERENCE
CONTINUOUS
LOW-PASS
FILTER
TIME
AD73311L
V
REF
0/38dB
PGA