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參數(shù)資料
| 型號(hào)： | OPA660 |
| 元件分類： | 運(yùn)動(dòng)控制電子 |
| 英文描述： | Wide Bandwidth OPERATIONAL TRANSCONDUCTANCE AMPLIFIER AND BUFFER |
| 中文描述： | 寬帶運(yùn)算跨導(dǎo)放大器和緩沖 |
| 文件頁數(shù)： | 9/18頁 |
| 文件大小： | 358K |
| 代理商： | OPA660 |
9
OPA660
BUFFER SECTION—AN OVERVIEW
The buffer section of the OPA660 is an open-loop buffer
consisting of complementary emitter-followers. It uses no
feedback, so its low frequency gain is slightly less than unity
and somewhat dependent on loading. It is designed prima-
rily for interstage buffering. It is not designed for driving
long cables or low impedance loads (although with small
signals, it may be satisfactory for these applications).
TRANSCONDUCTANCE
(OTA) SECTION—AN OVERVIEW
The symbol for the OTA section is similar to a transistor.
Applications circuits for the OTA look and operate much
like transistor circuits—the transistor, too, is a voltage-
controlled current source. Not only does this simplify the
understanding of applications circuits, but it aids the circuit
optimization process. Many of the same intuitive techniques
used with transistor designs apply to OTA circuits as well.
The three terminals of the OTA are labeled B, E, and C. This
calls attention to its similarity to a transistor, yet draws
distinction for clarity.
While it is similar to a transistor, one essential difference is
the sense of the C output current. It flows out the C terminal
for positive B-to-E input voltage and in the C terminal for
negative B-to-E input voltage. The OTA offers many advan-
tages over a discrete transistor. The OTA is self-biased,
simplifying the design process and reducing component
count. The OTA is far more linear than a transistor.
Transconductance of the OTA is constant over a wide range
of collector currents—this implies a fundamental improve-
ment of linearity.
BASIC CONNECTIONS
Figure 2 shows basic connections required for operation.
These connections are not shown in subsequent circuit
diagrams. Power supply bypass capacitors should be located
as close as possible to the device pins. Solid tantalum
capacitors are generally best. See “Circuit Layout” at the end
of the applications discussion and Figure 26 for further
suggestions on layout.
QUIESCENT CURRENT CONTROL PIN
The quiescent current of the OPA660 is set with a resistor,
R
Q
, connected from pin 1 to V–. It affects the operating
currents of both the buffer and OTA sections. This controls
the bandwidth and AC behavior as well as the
transconductance of the OTA section.
R
Q
= 250
sets approximately 20mA total quiescent current at
25
°
C. With a fixed 250
resistor, process variations could
cause this current to vary from approximately 16mA to 26mA.
It may be appropriate in some applications to trim this resistor
to achieve the desired quiescent current or AC performance.
Applications circuits generally do not show resistor, R
Q
,
but it is required for proper operation.
With a fixed R
Q
resistor, quiescent current increases with
temperature (see typical performance curve, Quiescent Current
vs Temperature). This variation of current with temperature
holds the transconductance, gm, of the OTA relatively con-
stant with temperature (another advantage over a transistor).
It is also possible to vary the quiescent current with a control
signal. The control loop in Figure 3 shows a 1/2 of a REF200
current source used to develop 100mV on R
1
. The loop
forces 100mV to appear on R
2
. Total quiescent current of the
OPA660 is approximately 85 I
1
, where I
1
is the current
made to flow out of pin 1.
FIGURE 2. Basic Connections.
50k
100
1
4
–V
CC
I
1
425
R
2
1/2
OPA1013
(1)
1/2 REF200
100μA
V+
1k
R
1
Internal
Current Source
Circuitry
I 85 I
= 85 (100μA)
= 20mA
1
R
1
R
2
NOTE: (1) Requires input common-mode range and
output swing close to V–, thus the choice of OPA1013.
OPA660
FIGURE 3. Optional Control Loop for Setting Quiescent
Current.
With this control loop, quiescent current will be nearly
constant with temperature. Since this differs from the tem-
perature-dependent behavior of the internal current source,
other temperature-dependent behavior may differ from that
shown in typical performance curves.
The circuit of Figure 3 will control the I
Q
of the OPA660
somewhat more accurately than with a fixed external resis-
tor, R
Q
. Otherwise, there is no fundamental advantage to
1
2
3
4
8
7
6
5
+
2.2μF
Solid
Tantalum
–5V
(1)
470pF
250
R
Q
R = 250
sets roughly
I 20mA
+
Solid
Tantalum
+5V
(1)
NOTE: (1) V
S
= ±6V absolute max.
1
2.2μF
10nF
470pF
10nF
(25
to
200
)
R
B
(25
to 200
)
R
B
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| OPA660AP | 功能描述:IC OPAMP TRANSCOND 850MHZ 8DIP RoHS:否 類別:集成電路 (IC) >> Linear - Amplifiers - Instrumentation 系列:- 產(chǎn)品變化通告:Discontinuation 18/May/2012 標(biāo)準(zhǔn)包裝:2,000 系列:- 放大器類型:通用 電路數(shù):4 輸出類型:滿擺幅 轉(zhuǎn)換速率:0.42 V/µs 增益帶寬積:1.5MHz -3db帶寬:- 電流 - 輸入偏壓:15nA 電壓 - 輸入偏移:1000µV 電流 - 電源:116µA 電流 - 輸出 / 通道:100mA 電壓 - 電源，單路/雙路(±):1.8 V ~ 5 V，±0.9 V ~ 2.5 V 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:14-TSSOP（0.173"，4.40mm 寬） 供應(yīng)商設(shè)備封裝:14-TSSOP 包裝:帶卷 (TR) 產(chǎn)品目錄頁面:851 (CN2011-ZH PDF) 其它名稱:296-20930-2 |
| OPA660AU | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
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