VREF p-p CM* *CM = COMMON-MODE VOLTAGE V" />
參數(shù)資料
型號: AD7450ARZ-REEL7
廠商: Analog Devices Inc
文件頁數(shù): 3/22頁
文件大?。?/td> 0K
描述: IC ADC 12BIT DIFF IN 1MSPS 8SOIC
標(biāo)準(zhǔn)包裝: 1,000
位數(shù): 12
采樣率(每秒): 1M
數(shù)據(jù)接口: DSP,MICROWIRE?,QSPI?,串行,SPI?
轉(zhuǎn)換器數(shù)目: 1
功率耗散(最大): 9.25mW
電壓電源: 單電源
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 8-SOIC(0.154",3.90mm 寬)
供應(yīng)商設(shè)備封裝: 8-SOIC
包裝: 帶卷 (TR)
輸入數(shù)目和類型: 1 個差分,單極
配用: EVAL-AD7450CBZ-ND - BOARD EVALUATION FOR AD7450
AD7450
–11–
CM*
VREF p-p
CM*
*CM = COMMON-MODE VOLTAGE
VIN+
VIN–
VDD
SCLK
SDATA
CS
GND
VREF
SERIAL
INTERFACE
3V/5V
SUPPLY
1.25V/2.5V
VREF
0.1 F
10 F
AD7450
VREF p-p
0.1 F
C/ P
Figure 6. Typical Connection Diagram
THE ANALOG INPUT
The analog input of the AD7450 is fully differential. Differential
signals have a number of benefits over single-ended signals,
including noise immunity based on the device’s common-mode
rejection, improvements in distortion performance, doubling of
the device’s available dynamic range, and flexibility in input ranges
and bias points.
Figure 7 defines the fully differential analog input of the AD7450.
VIN+
AD7450
VIN–
VREF p-p
COMMON-MODE
VOLTAGE
VREF p-p
Figure 7. Differential Input Definition
The amplitude of the differential signal is the difference between
the signals applied to the VIN+ and VIN– pins (i.e., VIN+ – VIN–).
VIN+ and VIN– are simultaneously driven by two signals each of
amplitude VREF that are 180
° out of phase. The amplitude of
the differential signal is therefore –VREF to +VREF p-p
(i.e., 2
VREF). This is regardless of the common mode (CM).
The common mode is the average of the two signals, i.e.,
(VIN+ + VIN–)/2, and is therefore the voltage that the two inputs
are centered on. This results in the span of each input being
CM
± VREF/2. This voltage has to be set up externally and its
range varies with VREF. As the value of VREF increases, the com-
mon-mode range decreases. When driving the inputs with an
amplifier, the actual common-mode range will be determined
by the amplifier’s output voltage swing.
Figures 8 and 9 show how the common-mode range typically
varies with VREF for both a 5 V and a 3 V power supply. The
common mode must be in this range to guarantee the
functionality of the AD7450.
For ease of use, the common mode can be set up to be equal to
VREF, resulting in the differential signal being
±V
REF centered
on VREF. When a conversion takes place, the common mode is
rejected resulting in a virtually noise free signal of amplitude
–VREF to +VREF corresponding to the digital codes of 0 to 4095.
VREF
5.0
0
0.25
0.75
1.75
2.25
2.75
3.25 3.50
1.25
COMMON-MODE
RANGE
V
4.5
2.0
1.5
1.0
0.5
3.5
2.5
4.0
3.0
COMMON-MODE RANGE
3.25V
1.75V
Figure 8. Input Common-Mode Range vs. VREF
(VDD = 5 V and VREF (Max) = 3.5 V)
VREF
0
2.0
1.5
1.0
0.5
2.5
3.0
0.25
0.50
1.00
1.25
1.50
2.00
2.20
0.75
1.75
COMMON-MODE
RANGE
V
COMMON-MODE RANGE
2V
1V
Figure 9. Input Common-Mode Range vs. VREF (VDD = 3 V
and VREF (Max) = 2.2 V)
Figure 10 shows examples of the inputs to VIN+ and VIN– for
different values of VREF for VDD = 5 V. It also gives the maxi-
mum and minimum common-mode voltages for each reference
value according to Figure 8.
Rev. A
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