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參數(shù)資料
| 型號： | LMV796 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 17 MHz, Low Noise, CMOS Input, 1.8V Operational Amplifiers |
| 中文描述： | 17兆赫，低噪聲，CMOS輸入，1.8V的運算放大器 |
| 文件頁數(shù)： | 15/19頁 |
| 文件大?。?/td> | 1152K |
| 代理商： | LMV796 |
Application Information
(Continued)
TRANSIMPEDANCE AMPLIFIER
CMOS input op amps are often used in transimpedance
applications as they have an extremely high input imped-
ance. A transimpedance amplifier converts a small input
current into a voltage. This current is usually generated by a
photodiode. The transimpedance gain, measured as the
ratio of the output voltage to the input current, is expected to
be large and wide-band. Since the circuit deals with currents
in the range of a few nA, low noise performance is essential.
The LMV796/LMV797 are CMOS input op amps providing
wide bandwidth and low noise performance, and are hence
ideal for transimpedance applications.
Usually, a transimpedance amplifier is designed on the basis
of the current source driving the input.Aphotodiode is a very
common capacitive current source, which requires transim-
pedance gain for transforming its miniscule current into eas-
ily detectable voltages. The photodiode and the amplifier’s
gain are selected with respect to the speed and accuracy
required of the circuit. A faster circuit would require a photo-
diode with lesser capacitance and a faster amplifier. A more
sensitive circuit would require a sensitive photodiode and a
high gain. A typical transimpedance amplifier is shown in
Figure 8
. The output voltage of the amplifier is given by the
equation V
= I
R
. Since the output swing of the am-
plifier is limited, R
should be selected such that all possible
values of I
IN
can be detected.
The LMV796/LMV797 have a large gain-bandwidth product
(17 MHz), which enables high gains at wide bandwidths. A
rail-to-rail output swing at 5.5V supply allows detection and
amplification of a wide range of input currents.ACMOS input
stage with negligible input current noise and low input volt-
age noise allows the LMV796/LMV797 to provide high fidel-
ity amplification for wide bandwidths. These properties make
the LMV796/LMV797 ideal for systems requiring wide-band
transimpedance amplification.
As mentioned earlier, the following parameters are used to
design a transimpedance amplifier: the amplifier gain-
bandwidth product, A
0
; the amplifier input capacitance, C
CM
;
the photodiode capacitance, C
D
; the transimpedance gain
required, R
F
; and the amplifier output swing. Once a feasible
R
F
is selected using the amplifier output swing, these num-
bers can be used to design an amplifier with the desired
transimpedance gain and a maximally flat frequency re-
sponse.
An essential component for obtaining a maximally flat re-
sponse is the feedback capacitor, C
. The capacitance seen
at the input of the amplifier, C
, combined with the feedback
capacitor, R
, generate a phase lag which causes gain-
peaking and can destabilize the circuit. C
is usually just the
sum of C
and C
. The feedback capacitor C
creates a
pole, f
in the noise gain of the circuit, which neutralizes the
zero in the noise gain, f
, created by the combination of R
F
and C
IN
. If properly positioned, the noise gain pole created
by C
can ensure that the slope of the gain remains at 20
dB/decade till the unity gain frequency of the amplifier is
reached, thus ensuring stability. As shown in
Figure 9
, f
is
positioned such that it coincides with the point where the
noise gain intersects the op amp’s open loop gain. In this
case, f
is also the overall 3 dB frequency of the transim-
pedance amplifier. The value of C
needed to make it so is
given by
Equation (3)
. A larger value of C
causes excessive
reduction of bandwidth, while a smaller value fails to prevent
gain peaking and instability.
20183566
FIGURE 6. Non-inverting Audio Preamplifier
20183558
FIGURE 7. Frequency Response of the Inverting Audio
Preamplifier
20183569
FIGURE 8. Photodiode Transimpedance Amplifier
L
www.national.com
15
相關PDF資料 |
PDF描述 |
|---|---|
| LMV796MF | 17 MHz, Low Noise, CMOS Input, 1.8V Operational Amplifiers |
| LMV796MFX | 17 MHz, Low Noise, CMOS Input, 1.8V Operational Amplifiers |
| LMV797 | 17 MHz, Low Noise, CMOS Input, 1.8V Operational Amplifiers |
| LMV797MM | 17 MHz, Low Noise, CMOS Input, 1.8V Operational Amplifiers |
| LMV797MMX | 17 MHz, Low Noise, CMOS Input, 1.8V Operational Amplifiers |
相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LMV796MF | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風格:SMD/SMT 封裝 / 箱體:QFN-16 轉換速度:0.89 V/us 關閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMV796MF/NOPB | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風格:SMD/SMT 封裝 / 箱體:QFN-16 轉換速度:0.89 V/us 關閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMV796MFX | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風格:SMD/SMT 封裝 / 箱體:QFN-16 轉換速度:0.89 V/us 關閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMV796MFX/NOPB | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風格:SMD/SMT 封裝 / 箱體:QFN-16 轉換速度:0.89 V/us 關閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
| LMV796QMF/NOPB | 功能描述:運算放大器 - 運放 RoHS:否 制造商:STMicroelectronics 通道數(shù)量:4 共模抑制比（最小值）:63 dB 輸入補償電壓:1 mV 輸入偏流（最大值）:10 pA 工作電源電壓:2.7 V to 5.5 V 安裝風格:SMD/SMT 封裝 / 箱體:QFN-16 轉換速度:0.89 V/us 關閉:No 輸出電流:55 mA 最大工作溫度:+ 125 C 封裝:Reel |
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