AD7352BRUZ-RL Analog Devices Inc, AD7352BRUZ-RL Datasheet - Page 14

• Manufacturer Part Number: AD7352BRUZ-RL
• Description: 12-Bit Dual Diff Simult 3 MSPS ADC I.C.
• Manufacturer: Analog Devices Inc

Specifications of AD7352BRUZ-RL

• Design Resources: DC-Coupled, Single-Ended-to-Differential Conversion Using AD8138 and AD7352 (CN0040)
• Number Of Bits: 12
• Sampling Rate (per Second): 3M
• Data Interface: DSP, MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Converters: 2
• Power Dissipation (max): 45mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP (0.173", 4.40mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD7352
DRIVING DIFFERENTIAL INPUTS
Differential operation requires V
simultaneously with two equal signals that are 180° out of
phase. Because not all applications have a signal preconditioned
for differential operation, there is often a need to perform a
single-ended-to-differential conversion.
Differential Amplifier
An ideal method of applying differential drive to the AD7352
is to use a differential amplifier such as the AD8138. This part
can be used as a single-ended-to-differential amplifier or as a
differential-to-differential amplifier. The AD8138 also provides
common-mode level shifting. Figure 20 shows how the AD8138
can be used as a single-ended-to-differential amplifier. The
positive and negative outputs of the AD8138 are connected to
the respective inputs on the ADC via a pair of series resistors
to minimize the effects of switched capacitance on the front end
of the ADC. The architecture of the AD8138 results in outputs
that are very highly balanced over a wide frequency range
without requiring tightly matched external components.
If the analog inputs source being used has zero impedance, all
four resistors (R
as each other. If the source has a 50 Ω impedance and a 50 Ω
termination, for example, increase the value of R
balance this parallel impedance on the input and thus ensure
that both the positive and negative analog inputs have the
same gain. The outputs of the amplifier are perfectly matched,
balanced differential outputs of identical amplitude, and are
exactly 180° out of phase.
Op Amp Pair
An op amp pair can be used to directly couple a differential
signal to one of the analog input pairs of the AD7352. The
circuit configurations in Figure 21 and Figure 22 show how an
op amp pair can be used to convert a single-ended signal into
a differential signal for both a bipolar and unipolar input signal,
respectively.
*MOUNT AS CLOSE TO THE AD7352 AS POSSIBLE
AND ENSURE THAT HIGH PRECISION R
R
R
S
G
Figure 20. Using the AD8138 as a Single-Ended-to-Differential Amplifier
2 = 523Ω
– 33Ω; R
+2.048V
GND
–2.048V
G
1 = R
F
1 = R
G
1, R
51Ω
F
2 = 499Ω; C
G
2, R
V
R
R
OCM
G
G
1
2
F
1, and R
F
AD8138
1 = C
C
R
C
R
F
F
F
F
S
10kΩ
1
1
2
2
RESISTORS ARE USED.
F
IN+
10kΩ
2 = 39pF;
F
and V
2) should be the same value
R
R
S
S
*
*
IN−
2.048V
0V
1.024V
2.048V
0V
1.024V
to be driven
G
V
2 by 25 Ω to
V
IN–
IN+
AD7352
REF
A
/REF
10µF
Rev. 0 | Page 14 of 20
B
The voltage applied to Point A sets up the common-mode
voltage. In both diagrams, it is connected in some way to the
reference. The
used in this configuration to provide differential drive to the
AD7352.
V
ADC TRANSFER FUNCTION
The output coding for the AD7352 is straight binary. The designed
code transitions occur at successive LSB values (1 LSB, 2 LSBs,
and so on). The LSB size is (2 × V
characteristic is shown in Figure 23.
GND
*ADDITIONAL PINS OMITTED FOR CLARITY.
*ADDITIONAL PINS OMITTED FOR CLARITY.
Figure 22. Dual Op Amp Circuit to Convert a Single-Ended Bipolar Signal into
GND
REF
Figure 21. Dual Op Amp Circuit to Convert a Single-Ended Unipolar Signal
111 ... 111
111 ... 110
111 ... 101
000 ... 010
000 ... 001
000 ... 000
2 × V
2 × V
–V
220Ω
REF
Figure 23. AD7352 Ideal Transfer Characteristic
REF
REF
AD8022
p-p
p-p
440Ω
440Ω
+ 0.5 LSB
A
A
–V
a Differential Unipolar Signal
REF
into a Differential Signal
220Ω
220Ω
220Ω
220Ω
220Ω
220Ω
20kΩ
is a suitable dual op amp that could be
+ 1 LSB
V+
V–
V+
V–
V+
V–
V+
V–
10kΩ
ANALOG INPUT
10kΩ
27Ω
27Ω
27Ω
27Ω
REF
)/4096. The ideal transfer
+V
2.048V
1.024V
0V
REF
2.048V
1.024V
0V
2.048V
1.024V
0V
2.048V
1.024V
0V
– 1.5 LSB
+V
V
V
V
V
IN+
IN–
REF
IN+
IN–
AD7352*
AD7352*
– 1 LSB
REF
REF
A
A
/REF
/REF
10µF
10µF
B
B