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參數資料
| 型號： | OPA847IDBVT |
| 英文描述： | Wideband, Ultra-Low Noise, Voltage-Feedback |
| 中文描述： | 寬帶，超低噪聲，電壓反饋 |
| 文件頁數： | 17/23頁 |
| 文件大?。?/td> | 529K |
| 代理商： | OPA847IDBVT |
OPA847
SBOS251C
17
www.ti.com
The criterion for setting the R
S
resistor is a maximum band-
width, flat frequency response at the load. For the OPA847
operating in a gain of +20, the frequency response at the
output pin is very flat to begin with, allowing relatively small
values of R
S
to be used for low capacitive loads. As the
signal gain is increased, the unloaded phase margin also
increases. Driving capacitive loads at higher gains requires
lower R
S
values than those shown for a gain of +20.
DISTORTION PERFORMANCE
The OPA847 is capable of delivering an exceptionally low
distortion signal at high frequencies over a wide range of
gains. The distortion plots in the Typical Characteristics show
the typical distortion under a wide variety of conditions. Most
of these plots are limited to a 110dB dynamic range. The
OPA847’s distortion driving a 200
load does not rise above
–90dBc until either the signal level exceeds 2.0V
PP
and/or
the fundamental frequency exceeds 5MHz. Distortion in the
audio band is < –130dBc.
Generally, until the fundamental signal reaches very high
frequencies or powers, the 2nd-harmonic dominates the dis-
tortion 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 noninverting configura-
tion this is the sum of R
F
+ R
G
, while in the inverting
configuration this is only R
F
(see Figure 2). Increasing the
output voltage swing increases harmonic distortion directly. A
6dB increase in output swing generally increases the 2nd-
harmonic 12dB and the 3rd-harmonic 18dB. Increasing the
signal gain also increases the 2nd-harmonic distortion. Finally,
the distortion increases as the fundamental frequency in-
creases due to the rolloff in the loop gain with frequency.
Conversely, the distortion improves going to lower frequencies
down to the dominant open-loop pole at approximately 80kHz.
The OPA847 has an extremely low 3rd-order harmonic
distortion. This also gives a high 2-tone 3rd-order
intermodulation intercept, as shown in the Typical Character-
istics. This intercept curve is defined at the 50
load when
driven through a 50
matching resistor to allow direct
comparisons to R
F
devices. This matching network attenu-
ates the voltage swing from the output pin to the load by 6dB.
If the OPA847 drives directly into the input of a high-
impedance device, such as an ADC, this 6dB attenuation is
not taken. Under these conditions, the intercept as reported
in the Typical Characteristics increases by a minimum of
6dBm. The intercept is used to predict the intermodulation
spurious power levels for two closely spaced frequencies. If
the two test frequencies, f
1
and f
2
, are specified in terms of
average and delta frequency, f
O
= (f
1
+ f
2
)/2 and
F
=
|f
2
– f
1
| /2,
the two 3rd-order, close-in spurious tones appear at f
O
± 3
F
.
The difference between the two equal test-tone power levels
and these intermodulation spurious power levels is given by
dBc = 2(IM3 – P
O
), where IM3 is the intercept taken from the
Typical Characteristics and P
O
is the power level in dBm at
the 50
load for one of the two closely spaced test frequen-
cies. For instance, at 30MHz, the OPA847 at a gain of +20
has an intercept of 34dBm at a matched 50
load.
If the full envelope of the two frequencies needs to be 2V
PP
,
this requires each tone to be 4dBm. The 3rd-order
intermodulation spurious tones will then be 2(34 – 4) =
60dBc below the test-tone power level (–56dBm). If this
same 2V
PP
2-tone envelope is delivered directly into the
input of an ADC without the matching loss or the loading of
the 50
network, the intercept would increase to at least
40dBm. With the same signal and gain conditions, but now
driving directly into a light load, the spurious tones will then
be at least 2(40 – 4) = 72dBc below the 4dBm test-tone
power levels centered on 30MHz. Tests have shown that
they are in fact much lower due to the lighter loading
presented by most ADCs.
DC ACCURACY AND OFFSET CONTROL
The OPA847 can provide excellent DC signal accuracy due
to its high open-loop gain, high common-mode rejection, high
power-supply rejection, and low input offset voltage and bias
current offset errors. To take full advantage of its low ±0.5mV
input offset voltage, careful attention to the input bias current
cancellation is also required. The low-noise input stage for
the OPA847 has a relatively high input bias current (19μA
typical into the pins), but with a very close match between the
two input currents—typically ±100nA input offset current.
Figures 13 and 14 show typical distributions of input offset
voltage and current for the OPA847.
FIGURE 13. Input Offset Voltage Distribution in μV.
1200
1000
800
600
400
200
0
μ
V
C
<
<
<
<
<
<
<
<
<
<
0
<
<
<
<
<
<
<
<
<
<
>
Mean = 48
μ
V
Standard Deviation = 110
μ
V
Total Count = 4040
FIGURE 14. Input Offset Current Distribution in nA.
900
800
700
600
500
400
300
200
100
0
nA
C
<
<
<
<
<
<
<
<
<
<
0
<
<
<
<
<
<
<
<
<
<
>
Mean = 50nA
Standard Deviation = 120nA
Total Count = 4040
相關PDF資料 |
PDF描述 |
|---|---|
| OPA847IDR | Wideband, Ultra-Low Noise, Voltage-Feedback |
| OPAMP1EVB | Op Amp Evaluation Board Manual SOT23, SC70, and SOIC8 Package |
| OPAMP3EVB | Op Amp Evaluation Board Manual TSSOP−16 Package |
| OPB10100-SERIES | Optoelectronic |
| OPB10510 | 8K, 1K X 8 2.5V SERIAL EE, IND, -40C to +85C, 8-TSSOP, TUBE |
相關代理商/技術參數 |
參數描述 |
|---|---|
| OPA847IDBVT | 制造商:Texas Instruments 功能描述:OP AMP WIDEBAND VFB SOT-23-6 847 |
| OPA847IDBVT | 制造商:Texas Instruments 功能描述:Operational Amplifier (Op-Amp) IC |
| OPA847IDBVTG4 | 功能描述:高速運算放大器 Wdebnd Ult-Lo Noise Voltage Feedback RoHS:否 制造商:Texas Instruments 通道數量:1 電壓增益 dB:116 dB 輸入補償電壓:0.5 mV 轉換速度: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 安裝風格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
| OPA847IDG4 | 功能描述:高速運算放大器 Wdebnd Ult-Lo Noise Voltage Feedback RoHS:否 制造商:Texas Instruments 通道數量:1 電壓增益 dB:116 dB 輸入補償電壓:0.5 mV 轉換速度: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 安裝風格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
| OPA847IDR | 功能描述:高速運算放大器 Wdebnd Ult-Lo Noise Voltage Feedback RoHS:否 制造商:Texas Instruments 通道數量:1 電壓增益 dB:116 dB 輸入補償電壓:0.5 mV 轉換速度: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 安裝風格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Tube |
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