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參數資料
| 型號： | AD8132 |
| 廠商： | Analog Devices, Inc. |
| 元件分類： | 運動控制電子 |
| 英文描述： | Low-Cost, High-Speed Differential Amplifier |
| 中文描述： | 低成本，高速差分放大器 |
| 文件頁數： | 19/20頁 |
| 文件大小： | 391K |
| 代理商： | AD8132 |
REV. 0
AD8132
–19–
V
OCM
is driven by a resistor divider that
“
measures
”
the output
common- mode voltage. Thus, the common-mode output volt-
age takes on the value that is set by the driven circuit. In this
case it comes from the center point of the termination at the
receive end of a 10 m length of Category 5 twisted pair cable.
If the receive end common-mode voltage is set to
“
ground,
”
it
will be well-de
fi
ned at the receive end. Any common-mode
signal that is picked up over the cable length due to noise, will
appear at the transmit end, and must be
“
absorbed
”
by the
transmitter. Thus, it is important that the transmitter have
adequate common-mode output range to absorb the full ampli-
tude of the common-mode signal coupled onto the cable and
thus prevent clipping.
Another way to look at this is that the circuit performs what is
sometimes called
“
transformer action.
”
One main difference is
that the AD8132 passes dc while transformers do not.
A transformer can also be easily con
fi
gured to have either a high
or low common-mode output impedance. If the transformer
’
s
center tap is connected to a solid voltage reference, it will set the
common-mode voltage on the secondary side of the transformer.
In this case, if one of the differential outputs is grounded, the
other output will have only half of the differential output signal.
This keeps the common-mode voltage at ground, where it is
required to be due to the center tap connection. This is analo-
gous to the AD8132 operating with a low output impedance
common-mode. See Figure 17.
V
DIFF
V
OCM
Figure 17. Transformer Whose Low Output Impedance
Secondary Is Set at V
OCM
If the center tap of the secondary of a transformer is allowed to
float (or there is no center tap), the transformer will have a high
common-mode output impedance. This means that the common-
mode of the secondary will be determined by what it is connected
to, and not by anything to do with the transformer itself.
If one of the differential ends of the transformer is grounded, the
other end will swing with the full output voltage. This means
that the common-mode of the output voltage is one-half of the
differential output voltage. But this shows that the common-mode
is not forced via a low impedance to a given voltage. The common-
mode output voltage can easily be changed to any voltage through
its other output terminals.
The AD8132 can exhibit the same performance when one of the
outputs in Figure 16 is grounded. The other output will swing
at the full differential output voltage. The common-mode signal
is
“
measured
”
by the voltage divider across the outputs and input
to V
OCM
. This then drives V
OUT,cm
to the same level. At higher
frequencies, it is important to minimize the capacitance on the
V
OCM
node or else phase shifts can compromise the performance.
The voltage divider resistances can also be lowered for better
frequency response.
V
DIFF
V
OCM
Figure 18. Transformer with High Output Impedance
Secondary
Full-Wave Rectifier
The balanced outputs of the AD8132, along with a couple of
Schottky diodes, can create a very high-speed full-wave recti
fi
er.
Such circuits are useful for measuring ac voltages and other
computational tasks.
Figure 19 shows the con
fi
guration of such a circuit. Each of the
AD8132 outputs drives the anode of an HP 2835 Schottky diode.
These Schottky diodes were chosen for their high-speed opera-
tion. At lower frequencies (approximately lower than 10 MHz),
a silicon signal diode, like a 1N4148 can be used. The cathodes
of the two diodes are connected together and this output node is
connected to ground by a 50
resistor.
R
G1
348
R
F1
348
R
F2
348
R
G2
348
+5V
–
5V
R
L
100
R
T2
24.9
R
T1
49.9
V
IN
HP2835
V
OUT
5V
CR1
10k
Figure 19. Full-Wave Rectifier
The diodes should be operated such that they are slightly forward-
biased when the differential output voltage is zero. For the
Schottky diodes, this is about 400 mV. The forward biasing can
be conveniently adjusted by CR1, which, in this circuit, raises
and lowers V
OUT,CM
without creating a differential output voltage.
One advantage of this circuit is that the feedback loop is never
momentarily opened while the diodes reverse their polarity within
the loop. This is the scheme that is sometimes used for full-wave
recti
fi
ers that use conventional op amps. These conventional
circuits do not work well at frequencies above about 1 MHz.
If there is not enough forward bias (V
OUT,cm
too low), the lower
sharp cusps of the full-wave recti
fi
ed output waveform will be
rounded off. Also, as the frequency increases, there tends to be
some rounding of the lower cusps. The forward bias can be
increased to yield sharper cusps at higher frequencies.
There is not a reliable, entirely quanti
fi
able, means to measure
the performance of a full-wave recti
fi
er. Since the ideal wave-
form has periodic sharp discontinuities, it should have (mostly
even) harmonics that have no upper bound on the frequency.
However, for a practical circuit, as the frequency increases, the
higher harmonics become attenuated and the sharp cusps that
are present at low frequencies become signi
fi
cantly rounded.
相關PDF資料 |
PDF描述 |
|---|---|
| AD8132-EVAL | Low-Cost, High-Speed Differential Amplifier |
| AD8132AR | Low-Cost, High-Speed Differential Amplifier |
| AD8132AR-REEL | Low-Cost, High-Speed Differential Amplifier |
| AD8132AR-REEL7 | Low-Cost, High-Speed Differential Amplifier |
| AD8132ARM | Low-Cost, High-Speed Differential Amplifier |
相關代理商/技術參數 |
參數描述 |
|---|---|
| AD8132_06 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Low Cost, High Speed Differential Amplifier |
| AD8132_09 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Low Cost, High Speed Differential Amplifier |
| AD8132AR | 功能描述:IC AMP DIFF LDIST LP 70MA 8SOIC RoHS:否 類別:集成電路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 標準包裝:73 系列:Over-The-Top® 放大器類型:通用 電路數:4 輸出類型:滿擺幅 轉換速率:0.07 V/µs 增益帶寬積:200kHz -3db帶寬:- 電流 - 輸入偏壓:1nA 電壓 - 輸入偏移:285µV 電流 - 電源:50µA 電流 - 輸出 / 通道:25mA 電壓 - 電源，單路/雙路(±):2 V ~ 44 V，±1 V ~ 22 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:16-WFDFN 裸露焊盤 供應商設備封裝:16-DFN-EP（5x3） 包裝:管件 |
| AD8132AR | 制造商:Analog Devices 功能描述:SEMICONDUCTORS ((NW)) |
| AD8132AR-EBZ | 功能描述:BOARD EVAL FOR AD8132AR RoHS:是 類別:編程器，開發系統 >> 評估板 - 運算放大器 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:1 系列:- |
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