參數(shù)資料
型號(hào)： OPA680
英文描述： Wideband, Voltage Feedback OPERATIONAL AMPLIFIER With Disable TM
中文描述： 寬帶，電壓反饋運(yùn)算放大器，禁用商標(biāo)
文件頁(yè)數(shù)： 17/21頁(yè)
文件大?。?/td> 235K
代理商： OPA680
17
OPA680
load from the feedback loop by inserting a series isolation
resistor between the amplifier output and the capacitive
load. This does not eliminate the pole from the loop re-
sponse, but rather shifts it and adds a zero at a higher
frequency. The additional zero acts to cancel the phase lag
from the capacitive load pole, thus increasing the phase
margin and improving stability.
The Typical Performance Curves show the recommended
R
S
versus capacitive load and the resulting frequency re-
sponse at the load. Parasitic capacitive loads greater than
2pF can begin to degrade the performance of the OPA680.
Long PC board traces, unmatched cables, and connections to
multiple devices can easily exceed this value. Always con-
sider this effect carefully, and add the recommended series
resistor as close as possible to the OPA680 output pin (see
Board Layout Guidelines).
The criterion for setting this R
S
resistor is a maximum
bandwidth, flat frequency response at the load. For the
OPA680 operating in a gain of +2, the frequency response
at the output pin is already slightly peaked without the
capacitive load requiring relatively high values of R
S
to
flatten the response at the load. Increasing the noise gain will
reduce the peaking as described previously. The circuit of
Figure 9 demonstrates this technique, allowing lower values
of R
S
to be used for a given capacitive load.
OPA680
402
175
402
+5V
50
50
C
L
R
NG
V
O
R
–5V
Power supply decoupling not shown.
FIGURE 9. Capacitive Load Driving with Noise Gain Tuning.
FIGURE 10. Required R
S
vs Noise Gain
This gain of +2 circuit includes a noise gain tuning resistor
across the two inputs to increase the noise gain, increasing
the unloaded phase margin for the op amp. Although this
technique will reduce the required R
S
resistor for a given
capacitive load, it does increase the noise at the output. It
also will decrease the loop gain, nominally decreasing the
distortion performance. If, however, the dominant distortion
mechanism arises from a high R
S
value, significant dynamic
range improvement can be achieved using this technique.
Figure 10 shows the required R
S
versus C
LOAD
parametric on
noise gain using this technique. This is the circuit of Figure
9 with R
NG
adjusted to increase the noise gain (increasing
the phase margin) then sweeping C
LOAD
and finding the
required R
S
to get a flat frequency response. This plot also
gives the required R
S
versus C
LOAD
for the OPA680 oper-
ated at higher signal gains.
DISTORTION PERFORMANCE
The OPA680 provides good distortion performance into a
100
load on
±
5V supplies. Relative to alternative solu-
tions, it provides exceptional performance into lighter loads
and/or operating on a single +5V supply. Generally, until the
fundamental signal reaches very high frequency or power
levels, the 2nd harmonic will dominate the distortion with a
negligible 3rd harmonic component. Focusing then on the
2nd harmonic, increasing the load impedance improves
distortion directly. Remember that the total load includes the
feedback network; in the non-inverting configuration (Fig-
ure 1) this is sum of R
F
+ R
G
, while in the inverting
configuration, it is just R
F
. Also, providing an additional
supply decoupling capacitor (0.1
μ
F) between the supply
pins (for bipolar operation) improves the 2nd-order distor-
tion slightly (3dB to 6dB).
In most op amps, increasing the output voltage swing in-
creases harmonic distortion directly. The new output stage
used in the OPA680 actually holds the difference between
fundamental power and the 2nd and 3rd harmonic powers
relatively constant with increasing output power until very
large output swings are required (>4Vp-p). This also shows
up in the two-tone, 3rd-order intermodulation spurious (IM3)
response curves. The 3rd-order spurious levels are extremely
low at low output power levels. The output stage continues
to hold them low even as the fundamental power reaches
very high levels. As the Typical Performance Curves show,
the spurious intermodulation powers do not increase as
predicted by a traditional intercept model. As the fundamen-
tal power level increases, the dynamic range does not de-
crease significantly. For 2 tones centered at 20MHz, with
10dBm/tone into a matched 50
load (i.e., 2Vp-p for each
tone at the load, which requires 8Vp-p for the overall two-
tone envelope at the output pin), the Typical Performance
Curves show 57dBc difference between the test tone powers
and the 3rd-order intermodulation spurious powers. This
exceptional performance improves further when operating at
lower frequencies.
100
90
80
70
60
50
40
30
20
10
0
Capacitive Load (pF)
1
10
100
S
)
NG = 2
NG = 3
NG = 4
相關(guān)PDF資料
PDF描述
OPA680N Wideband, Voltage Feedback OPERATIONAL AMPLIFIER With Disable TM
OPA680P Wideband, Voltage Feedback OPERATIONAL AMPLIFIER With Disable TM
OPA681U Wideband, Current Feedback OPERATIONAL AMPLIFIER With Disable
OPA681 Wideband, Current Feedback OPERATIONAL AMPLIFIER With Disable
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
OPA680N 制造商:BB 制造商全稱:BB 功能描述:Wideband, Voltage Feedback OPERATIONAL AMPLIFIER With Disable TM
OPA680N/250 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Voltage-Feedback Operational Amplifier
OPA680N/3K 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Voltage-Feedback Operational Amplifier
OPA680P 功能描述:高速運(yùn)算放大器 Wideband V Feedb 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
OPA680U 制造商:BB 制造商全稱:BB 功能描述:EVALUATION FIXTURE
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