參數(shù)資料
型號(hào): EVAL-AD7400EDZ
廠商: Analog Devices Inc
文件頁數(shù): 5/20頁
文件大?。?/td> 0K
描述: BOARD EVAL AD7400
標(biāo)準(zhǔn)包裝: 1
系列: iCoupler®
ADC 的數(shù)量: 1
位數(shù): 16
采樣率(每秒): 10M
數(shù)據(jù)接口: 串行
輸入范圍: ±320 mV
在以下條件下的電源(標(biāo)準(zhǔn)): 90mW @ 10MSPS
工作溫度: -40°C ~ 105°C
已用 IC / 零件: AD7400
已供物品:
Data Sheet
AD7400
Rev. G | Page 13 of 20
THEORY OF OPERATION
CIRCUIT INFORMATION
The AD7400 isolated Σ-Δ modulator converts an analog input
signal into a high speed (10 MHz typical), single-bit data
stream; the time average of the modulator’s single-bit data is
directly proportional to the input signal. Figure 22 shows a
typical application circuit where the AD7400 is used to provide
isolation between the analog input, a current sensing resistor,
and the digital output, which is then processed by a digital filter
to provide an N-bit word.
ANALOG INPUT
The differential analog input of the AD7400 is implemented
with a switched capacitor circuit. This circuit implements a
second-order modulator stage that digitizes the input signal
into a 1-bit output stream. The sample clock (MCLKOUT)
provides the clock signal for the conversion process as well as
the output data-framing clock. This clock source is internal on
the AD7400. The analog input signal is continuously sampled
by the modulator and compared to an internal voltage reference.
A digital stream that accurately represents the analog input over
time appears at the output of the converter (see Figure 20).
04
718-
01
9
MODULATOR OUTPUT
+FS ANALOG INPUT
–FS ANALOG INPUT
ANALOG INPUT
Figure 20. Analog Input vs. Modulator Output
A differential signal of 0 V results (ideally) in a stream of 1s and
0s at the MDAT output pin. This output is high 50% of the time
and low 50% of the time. A differential input of 200 mV pro-
duces a stream of 1s and 0s that are high 81.25% of the time. A
differential input of 200 mV produces a stream of 1s and 0s
that are high 18.75% of the time.
A differential input of 320 mV results in a stream of, ideally, all
1s. This is the absolute full-scale range of the AD7400, while
200 mV is the specified full-scale range, as shown in Table 9.
Table 9. Analog Input Range
Analog Input
Voltage Input
Full-Scale Range
+640 mV
Positive Full Scale
+320 mV
Positive Specified Input Range
+200 mV
Zero
0 mV
Negative Specified Input Range
200 mV
Negative Full Scale
320 mV
To reconstruct the original information, this output needs to be
digitally filtered and decimated. A Sinc3 filter is recommended
because this is one order higher than that of the AD7400
modulator. If a 256 decimation rate is used, the resulting
16-bit word rate is 39 kHz, assuming a 10 MHz internal clock
frequency. Figure 21 shows the transfer function of the AD7400
relative to the 16-bit output.
04718-020
65535
53248
SPECIFIED RANGE
ANALOG INPUT
ADC
CODE
12288
–320mV
–200mV
+200mV +320mV
0
Figure 21. Filtered and Decimated 16-Bit Transfer Characteristic
04
71
8-
0
18
Σ-
MOD/
ENCODER
INPUT
CURRENT
NONISOLATED
5V/3V
ISOLATED
5V
VDD1
RSHUNT
VIN+
VIN
GND1
VDD
GND
VDD2
MDAT
SINC3 FILTER
AD7400
MCLKOUT
SDAT
CS
SCLK
MCLK
GND2
DECODER
+
ENCODER
Figure 22. Typical Application Circuit
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