- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄363781 > OPA681N Wideband, Current Feedback OPERATIONAL AMPLIFIER With Disable PDF資料下載
參數(shù)資料
| 型號： | OPA681N |
| 英文描述： | Wideband, Current Feedback OPERATIONAL AMPLIFIER With Disable |
| 中文描述： | 寬帶，電流反饋運算放大器，禁用 |
| 文件頁數(shù)： | 14/21頁 |
| 文件大?。?/td> | 241K |
| 代理商： | OPA681N |
14
OPA681
attenuated if reflected to the input side of R
G
. Using the 1:2
(turns ratio) step-up transformer reflects the 50
source imped-
ance at the primary through to the secondary as a 200
source
impedance (and the 200
R
G
resistor is reflected through to the
transformer primary as a 50
input matching impedance). The
noise gain (NG) to the amplifier output is then 1+ 600/400 =
2.5V/V. Taking the op amp’s 2.2nV/
√
Hz input voltage noise
times this noise gain to the output, then reflecting this noise
term to the input side of the R
G
resistor, divides it by 3. This
gives a net gain of 0.833 for the non-inverting input voltage
noise when reflected to the input point for the op amp circuit.
This is further reduced when referred back to the transformer
primary.
The relatively low gain IF amplifier circuit of Figure 5 gives a
12dB noise figure at the input of the transformer. Increasing the
R
F
resistor to 600
(once R
G
is set to 200
for input impedance
matching) will slightly reduce the bandwidth. Measured results
show 150MHz small-signal bandwidth for the circuit of Figure
5 with exceptional flatness through 30MHz. Although the
OPA681 does not show an intercept characteristic for the
2-tone, 3rd-order intermodulation distortion, it does hold a very
high spurious free dynamic range through high output powers
and frequencies. The maximum single-tone power at the match-
ed load for the single-supply circuit of Figure 5 is 1dBm (this
requires a 2.8Vp-p swing at the output pin of the OPA681 for
the 2-tone envelope). Measured 2-tone SFDR at this maximum
load power for the circuit of Figure 5 exceeds 55dBc for
frequencies to 30MHz.
DESIGN-IN TOOLS
DEMONSTRATION BOARDS
Several PC boards are available to assist in the initial
evaluation of circuit performance using the OPA681 in its
three package styles. All of these are available free as an
unpopulated PC board delivered with descriptive documen-
tation. The summary information for these boards is shown
in the table below.
or as one model on a disk from the Burr-Brown Applications
department (1-800-548-6132). The Applications department
is also available for design assistance at this number. These
models do a good job of predicting small-signal AC and
transient performance under a wide variety of operating
conditions. They do not do as well in predicting the har-
monic distortion or dG/d
φ
characteristics. These models do
not attempt to distinguish between the package types in their
small-signal AC performance.
OPERATING SUGGESTIONS
SETTING RESISTOR VALUES TO
OPTIMIZE BANDWIDTH
A current feedback op amp like the OPA681 can hold an almost
constant bandwidth over signal gain settings with the proper
adjustment of the external resistor values. This is shown in the
Typical Performance Curves; the small-signal bandwidth de-
creases only slightly with increasing gain. Those curves also
show that the feedback resistor has been changed for each gain
setting. The resistor “values” on the inverting side of the circuit
for a current feedback op amp can be treated as frequency
response compensation elements while their “ratios” set the
signal gain. Figure 6 shows the small-signal frequency response
analysis circuit for the OPA681.
FIGURE 6. Current Feedback Transfer Function Analysis
Circuit.
R
F
V
O
R
G
R
I
Z
(S)
i
ERR
i
ERR
α
V
I
BOARD
PART
NUMBER
LITERATURE
REQUEST
NUMBER
PRODUCT
PACKAGE
OPA681P
OPA681U
OPA681N
8-Pin DIP
8-Pin SO-8
6-Lead SOT23-6
DEM-OPA68xP
DEM-OPA68xU
DEM-OPA68xN
MKT-350
MKT-351
MKT-348
Contact the Burr-Brown applications support line to request
any of these boards.
MACROMODELS AND APPLICATIONS SUPPORT
Computer simulation of circuit performance using SPICE is
often useful when analyzing the performance of analog
circuits and systems. This is particularly true for video and
RF amplifier circuits where parasitic capacitance and induc-
tance can have a major effect on circuit performance. A
SPICE model for the OPA681 is available through either the
Burr-Brown Internet web page (http://www.burr-brown.com)
The key elements of this current feedback op amp model are:
α
→
Buffer gain from the non-inverting input to the inverting input
R
I
→
Buffer output impedance
i
ERR
→
Feedback error current signal
Z(s)
→
Frequency dependent open loop transimpedance gain from i
ERR
to V
O
The buffer gain is typically very close to 1.00 and is
normally neglected from signal gain considerations. It will,
however, set the CMRR for a single op amp differential
amplifier configuration. For a buffer gain
α
< 1.0, the
CMRR = –20
x
log (1–
α
) dB.
R
I
, the buffer output impedance, is a critical portion of the
bandwidth control equation. The OPA681 is typically about
41
.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| OPA681P | Wideband, Current Feedback OPERATIONAL AMPLIFIER With Disable |
| OPA681DATASHEET | OPA681 Data Sheet - SpeedPlus Wideband. Current Feedback OPERATIONAL AMPLIFIER With Disable |
| OPA682U | Wideband, Fixed Gain BUFFER AMPLIFIER With Disable |
| OPA682 | Wideband, Fixed Gain BUFFER AMPLIFIER With Disable |
| OPA682N | Wideband, Fixed Gain BUFFER AMPLIFIER With Disable |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| OPA681N/250 | 制造商:Rochester Electronics LLC 功能描述:- Bulk 制造商:Texas Instruments 功能描述: |
| OPA681N/3K | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| OPA681P | 功能描述:高速運算放大器 DIP-8 WB Current-Fd RoHS:否 制造商:Texas Instruments 通道數(shù)量:1 電壓增益 dB:116 dB 輸入補(bǔ)償電壓:0.5 mV 轉(zhuǎn)換速度:55 V/us 工作電源電壓:36 V 電源電流:7.5 mA 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
| OPA681U | 功能描述:高速運算放大器 SOIC-8 WB Current-F RoHS:否 制造商:Texas Instruments 通道數(shù)量:1 電壓增益 dB:116 dB 輸入補(bǔ)償電壓:0.5 mV 轉(zhuǎn)換速度:55 V/us 工作電源電壓:36 V 電源電流:7.5 mA 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
| OPA681U/2K5 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Current-Feedback Operational Amplifier |
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。