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| 型號： | EVAL-AD7634CBZ |
| 廠商： | Analog Devices Inc |
| 文件頁數(shù)： | 13/32頁 |
| 文件大?。?/td> | 0K |
| 描述： | EVAL KIT AD7634 |
| 標(biāo)準(zhǔn)包裝： | 1 |
| 系列： | * |
| 其它名稱： | Q6500730 |
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AD7634
Data Sheet
Rev. B | Page 20 of 32
ANALOG INPUTS
Input Range Selection
In parallel mode and serial hardware mode, the input range is
selected by using the BIPOLAR (bipolar) and TEN (10 V range)
inputs. See Table 6 for pin details; see the Hardware Configuration
section and the Software Configuration section for program-
ming the mode selection with either pins or configuration
register. Note that when using the configuration register, the
BIPOLAR and TEN inputs are don’t cares and should be tied
to either high or low.
Input Structure
Figure 28 shows an equivalent circuit for the input structure of
the AD7634.
D1
RIN
CIN
D2
IN+ OR IN–
VEE
VCC
CPIN
AGND
D3
D4
AVDD
0V TO 5V
RANGE ONLY
0
64
06
-0
28
Figure 28. AD7634 Simplified Analog Input
The four diodes, D1 to D4, provide ESD protection for the analog
inputs, IN+ and IN. Care must be taken to ensure that the analog
input signal never exceeds the supply rails by more than 0.3 V,
because this causes the diodes to become forward-biased and
to start conducting current. These diodes can handle a forward-
biased current of 120 mA maximum. For instance, these conditions
could eventually occur when the input buffer’s U1 supplies are
different from AVDD, VCC, and VEE. In such a case, an input
buffer with a short-circuit current limitation can be used to protect
the part although most op amps’ short-circuit current is <100 mA.
Note that D3 and D4 are only used in the 0 V to 5 V range to
allow for additional protection in applications that are switching
from the higher voltage ranges.
This analog input structure of the AD7634 is a true differential
structure allowing the sampling of the differential signal between
IN+ and IN. By using this differential input, small signals
common to both inputs are rejected as shown in Figure 29,
which represents the typical CMRR over frequency.
120
0
1
10000
FREQUENCY (kHz)
CM
RR
(
d
B)
100
80
60
40
20
10
100
1000
06
40
6-
0
29
0V TO 10V
±5V
0V TO 5V
±10V
Figure 29. Analog Input CMRR vs. Frequency
During the acquisition phase for ac signals, the impedance of
the analog inputs, IN+ and IN, can be modeled as a parallel
combination of Capacitor CPIN and the network formed by
the series connection of RIN and CIN. CPIN is primarily the pin
capacitance. RIN is typically 70 Ω and is a lumped component
comprised of serial resistors and the on resistance of the switches.
CIN is primarily the ADC sampling capacitor and depending on
the input range selected is typically 48 pF in the 0 V to 5 V range,
typically 24 pF in the 0 V to 10 V and ±5 V ranges, and typically
12 pF in the ±10 V range. During the conversion phase, when the
switches are opened, the input impedance is limited to CPIN.
Because the input impedance of the AD7634 is very high, it
can be directly driven by a low impedance source without gain
error. To further improve the noise filtering achieved by the
AD7634 analog input circuit, an external, one-pole RC filter
between the amplifier’s outputs and the ADC analog inputs can
be used, as shown in Figure 27. However, large source imped-
ances significantly affect the ac performance, especially the
THD. The maximum source impedance depends on the amount
of THD that can be tolerated. The THD degrades as a function of
the source impedance and the maximum input frequency, as
shown in Figure 30.
–130
–110
–90
–70
0
25
50
75
100
15
33
100
200
06
40
6-
0
50
FREQUENCY (kHz)
T
H
D
(
d
B)
Figure 30. THD vs. Analog Input Frequency and Source Resistance
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| EVAL-AD7641EDZ | 功能描述:BOARD EVAL FOR AD7641 RoHS:是 類別:編程器，開發(fā)系統(tǒng) >> 評估板 - 模數(shù)轉(zhuǎn)換器 (ADC) 系列:* 產(chǎn)品培訓(xùn)模塊:Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:1 系列:- ADC 的數(shù)量:1 位數(shù):12 采樣率（每秒）:94.4k 數(shù)據(jù)接口:USB 輸入范圍:±VREF/2 在以下條件下的電源（標(biāo)準(zhǔn)）:- 工作溫度:-40°C ~ 85°C 已用 IC / 零件:MAX11645 已供物品:板，軟件 |
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