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參數(shù)資料
| 型號(hào)： | OPA685 |
| 英文描述： | Ultra-Wideband, Current-Feedback OPERATIONAL AMPLIFIER With Disable TM |
| 中文描述： | 超寬帶，電流反饋運(yùn)算放大器商標(biāo)使用禁用 |
| 文件頁數(shù)： | 18/28頁 |
| 文件大?。?/td> | 283K |
| 代理商： | OPA685 |
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18
OPA685
SAW FILTER BUFFER
One common requirement in an IF strip is to buffer the output
of a mixer with enough gain to recover the insertion loss of
a narrowband SAW filter. The front page of this data sheet
shows a recommended circuit using the OPA685. Operating
in the inverting mode at a voltage gain of –8V/V, this circuit
provides a 50
input match using the gain set resistor, has
the feedback optimized for maximum bandwidth (450MHz
in this case), and drives through a 50
output resistor into the
matching network at the input of the SAW filter. If the SAW
filter gives a 12dB insertion loss, a net gain of 0dB to the 50
load at the output of the SAW (which could be the input
impedance of the next IF amplifier or mixer) will be deliv-
ered in the passband of the SAW filter. Using the OPA685 in
this application will isolate the first mixer from the imped-
ance of the SAW filter and provide very low 3rd-order, 2-
tone spurious levels at the carrier frequency. Inverting opera-
tion as shown on the front page will give the broadest
bandwidth up to a gain of 12V/V (15.6dB). Non-inverting
operation will give higher bandwidth at gain settings higher
than this, but will give a slight reduction in intercept and
Noise Figure performance.
LO BUFFER AMPLIFIER
The OPA685 may also be used to buffer the Local Oscillator
(LO) from the mixer(s). Operating at a voltage gain of +2,
the OPA685 will provide almost perfect load isolation for
the LO with a net gain of 0dB to the mixer. Applications
through 1GHz LOs may be considered, but best operation
would be for LOs < 500MHz at a gain of +2. Gain could also
be easily provided by the OPA685 to drive higher power
levels into the mixer. One unique option in using the OPA685
as an LO buffer is shown in Figure 6. Since the OPA685 can
FIGURE 6. Dual Output LO Buffer.
drive multiple output loads, two identical LO signals may be
delivered to the mixers in a diversity receiver simply by
tapping the output off through two series 50
output resis-
tors. This circuit is set up for a voltage gain of +2V/V to the
output pin for a gain of +1V/V (0dB) to the mixers, but could
easily be adjusted to deliver higher gains as well.
WIDEBAND CABLE DRIVING
APPLICATIONS
The high slew rate and bandwidth of the OPA685 can be
used to meet the most demanding cable driving applications.
CABLE MODEM RETURN PATH DRIVER
The standard cable modem upstream driver is typically
required to drive high power over a 5MHz to 65MHz
bandwith while delivering < –50dBc distortion. Highly inte-
grated solutions (including programmable gain stages) often
fall short of this target due to high losses from the amplifier
output to the line. The higher gain operating capability of the
OPA685, along with its very high slew rate, provides a low-
cost solution for delivering this signal with the required
spurious free dynamic range. Figure 7 shows one example of
using the OPA685 as an upstream driver for a cable modem
return path. In this case, the input impedance of the driver is
set to 75
by the gain resistor (R
G
). The required input level
from the adjustable gain stage is significantly reduced by the
15.5dB gain provided by the OPA685. In this example, the
physical 75
output matching resistor, along with the 3dB
loss in the diplexer, will attenuate the output swing by 9dB
on the line. In this example, a single +12V supply was used
to achieve the lowest harmonic distortion for the 6Vp-p
OPA685
R
F
511
R
G
511
50
50
LO
50
LNA
Diversity Receiver
Antenna
Antenna
IF1
IF2
Bandpass
Filter
Bandpass
Filter
LNA
–5V
+5V
DIS
Power supply decoupling not shown.
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| OPA685U | Ultra-Wideband, Current-Feedback OPERATIONAL AMPLIFIER With Disable TM |
| OPA699ID | Wideband, High Gain VOLTAGE LIMITING AMPLIFIER |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| OPA685N | 制造商:BB 制造商全稱:BB 功能描述:Ultra-Wideband, Current-Feedback OPERATIONAL AMPLIFIER With Disable TM |
| OPA685N/250 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Current-Feedback Operational Amplifier |
| OPA685N/3K | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Current-Feedback Operational Amplifier |
| OPA685U | 功能描述:高速運(yùn)算放大器 Ultra-Wideband 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 |
| OPA685U/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 |
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