AD9221AR-REEL Analog Devices Inc, AD9221AR-REEL Datasheet - Page 23

• Manufacturer Part Number: AD9221AR-REEL
• Description: IC,A/D CONVERTER,SINGLE,12-BIT,CMOS,SOP,28PIN
• Manufacturer: Analog Devices Inc

Specifications of AD9221AR-REEL

• Rohs Status: RoHS non-compliant
• Number Of Bits: 12
• Sampling Rate (per Second): 1.5M
• Data Interface: Parallel
• Number Of Converters: 7
• Power Dissipation (max): 70mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SOIC (0.300", 7.50mm Width)
• For Use With: AD9221-EB - BOARD EVAL FOR AD9221

APPLICATIONS
Direct IF Down Conversion Using the AD9220
As previously noted, the AD9220’s performance in the differen-
tial mode of operation extends well beyond its baseband region
and into several Nyquist zone regions. Thus, the AD9220 may
be well suited as a mix down converter in both narrow and
wideband applications. Various IF frequencies exist over the
frequency range in which the AD9220 maintains excellent
dynamic performance (e.g., refer to Figure 17 and 18). The IF
signal will be aliased to the ADC’s baseband region due to the
sampling process in a similar manner that a mixer will down-
convert an IF signal. For signals in various Nyquist zones, the
following equation may be used to determine the final frequency
after aliasing.
There are several potential benefits in using the ADC to alias
(i.e., or mix) down a narrow-band or wideband IF signal. First
and foremost is the elimination of a complete mixer stage with
its associated amplifiers and filters, reducing cost and power
dissipation. Second is the ability to apply various DSP tech-
niques to perform such functions as filtering, channel selection,
quadrature demodulation, data reduction, and detection.
One common example is the digitization of a 21.4 MHz IF
using a low jitter 10 MHz sample clock. Using the equation
above for the fifth Nyquist zone, the resultant frequency after
sampling is 1.4 MHz. Figure 33 shows the typical performance
of the AD9220 operating under these conditions. Figure 34
demonstrates how the AD9220 is still able to maintain a high
degree of linearity and SFDR over a wide amplitude.
REV. E
Figure 33. IF Sampling a 21.4 MHz Input Using
the AD9220 (V
f
f
f
f
f
1 NYQUIST
2 NYQUIST
3 NYQUIST
4 NYQUIST
5 NYQUIST
–100
–120
–20
–40
–60
–80
0
1
7
= f
= f
= abs (f
= 2 × f
= abs (2 × f
SIGNAL
SAMPLE
CM
8
SAMPLE
SAMPLE
1
= 2.5 V, Input Span = 2 V p-p)
6
– f
FREQUENCY – MHz
SAMPLE
SIGNAL
– f
– f
SIGNAL
SIGNAL
– f
9
2
SIGNAL
5
ENCODE = 10MSPS
A
)
IN
= 21.4MHz
)
3
4
5
–23–
Multichannel Data Acquisition with Autocalibration
The AD9221/AD9223/AD9220 is well suited for high perfor-
mance, low power data acquisition systems. Aside from its
exceptional ac performance, it exhibits true 12-bit linearity and
temperature drift performance (i.e., excluding internal refer-
ence). Furthermore, the A/D product family provides the system
designer with an upward or downward component selection
path based on power consumption and sampling rate.
A typical multichannel data acquisition system is shown in
Figure 35. Also shown is some additional inexpensive gain and
offset autocalibration circuitry that is often required in high
accuracy data acquisition systems. These additional peripheral
components were selected based on their performance, power
consumption, and cost.
Referring to Figure 35, the AD9221/AD9223/AD9220 is config-
ured for single-ended operation with a 2.5 V p-p input span and
a 2.5 V common-mode voltage using an external, precision 2.5
voltage reference, U1. This configuration and input span allows
the buffer amplifier, U4, to be single supply. Also, it simplifies
the design of the low temperature drift autocalibration circuitry
that uses thin-film resistors for temperature stability and ratio-
metric accuracy. The input of the AD9221/AD9223/AD9220
can be easily configured for a wider span but it should remain
within the input/output swing capabilities of a high speed, rail-
to-rail, single-supply amplifier, U4 (e.g., AD8041).
The gain and offset calibration circuitry is based on two 8-bit,
current-output DAC08s, U3 and U5. The gain calibration
circuitry consisting of U3, and an op amp, U2A, is configured
to provide a low drift nominal 1.25 V reference to the AD9221/
AD9223/AD9220. The resistor values that set the gain calibra-
tion range were selected to provide a nominal adjustment span
of ±128 LSBs with 1 LSB resolution with respect to the A/D. Note
that the bandwidth of the reference is low and, as a result, it is
not possible to change the reference voltage rapidly in this mode.
Figure 34. AD9220 Differential Input SNR/SFDR
vs. Input Amplitude (A
90
80
70
60
50
40
30
20
10
0
–50
–40
AD9221/AD9223/AD9220
–30
IN
SFDR
A
) @ 21.4 MHz
IN
SNR
– dB
–20
–10
0