6227BZ10200F AA P194018 现场总线 F-bus PC 板卡

6227BZ10200F AA P194018 现场总线 F-bus PC 板卡 

除了宽带宽外，OPA858还具有2000 V/µs的高转换速率。转换速率是一个关键
具有窄亚10 ns脉冲的高速脉冲应用中的参数，如光时域
反射计（OTDR）和激光雷达。OPA858的高转换速率意味着该设备准确
再现如图20所示的2-V、亚ns脉冲边缘。OPA858的宽带宽和转换速率
使其成为高速信号链前端的理想放大器。
图52显示了作为频率函数的OPA858的开环输出阻抗。达到高
转换速率和跨频率的低输出阻抗，OPA858的输出摆幅限制为
大约3V。OPA858通常与高速流水线ADC和闪存ADC结合使用
其具有有限的输入范围。因此，OPA858输出摆幅范围与类电压耦合
噪声规格使信号链的整体动态范围大化。
频率（Hz）
电流噪声（A/O Hz）
OPA858
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功能描述（续）
图52.开环输出阻抗（ZOL）与频率
9.3.5电流噪声
CMOS和JFET输入放大器在低频时的输入阻抗超过几GΩs。然而，在
在较高频率下，晶体管对漏极、源极和衬底的寄生电容降低了
阻抗。低频时的高阻抗消除了任何偏置电流和相关的散粒噪声。在
频率越高，输入电流噪声越大（见图53），这是由于
CMOS栅极氧化物和下面的晶体管沟道。这种现象是
晶体管的结构是不可避免的。
图53.输入电流噪声（IBN和IBI）与频率
断电电压（V）
静态电流（mA）
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9.4设备功能模式
9.4.1分供和单供运行
OPA858可配置单面电源或分体式电源，如图63所示。分体式电源
使用输入共模设置为接地的平衡电源的操作简化了实验室测试，因为大多数
信号发生器、网络分析仪、频谱分析仪和其他实验室设备通常参考输入和
输出接地。在信号绕地摆动的系统中，分路供电操作是优选的。
然而，该系统需要两个供电轨。在分路供电操作中，热垫必须连接到
负电源。
较新的系统使用单个pow

6227BZ10200F AA P194018 现场总线 F-bus PC 板卡 

6227BZ10200F AA P194018 现场总线 F-bus PC 板卡 

In addition to wide bandwidth, the OPA858 features a high slew rate of 2000 V/µs . The slew rate is a critical
parameter in high-speed pulse applications with narrow sub 10-ns pulses such as Optical Time-Domain
Reflectometry (OTDR) and LIDAR. The high slew rate of the OPA858 implies that the device accurately
reproduces a 2-V, sub-ns pulse edge as seen in Figure 20. The wide bandwidth and slew rate of the OPA858
make it an ideal amplifier for high-speed, signal-chain front ends.
Figure 52 shows the open-loop output impedance of the OPA858 as a function of frequency. To achieve high
slew rates and low output impedance across frequency, the output swing of the OPA858 is limited to
approximately 3 V. The OPA858 is typically used in conjunction with high-speed pipeline ADCs and flash ADCs
that have limited input ranges. Therefore, the OPA858 output swing range coupled with the class-leading voltage
noise specification maximizes the overall dynamic range of the signal chain.
Frequency (Hz)
Current Noise (A/óHz)
OPA858
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Feature Description (continued)
Figure 52. Open-Loop Output Impedance (ZOL) vs Frequency
9.3.5 Current Noise
The input impedance of CMOS and JFET input amplifiers at low frequencies exceed several GΩs. However, at
higher frequencies, the transistors parasitic capacitance to the drain, source, and substrate reduces the
impedance. The high impedance at low frequencies eliminates any bias current and the associated shot noise. At
higher frequencies, the input current noise increases (see Figure 53) as a result of capacitive coupling between
the CMOS gate oxide and the underlying transistor channel. This phenomenon is a natural artifact of the
construction of the transistor and is unavoidable.
Figure 53. Input Current Noise (IBN and IBI) vs Frequency
Power Down Voltage (V)
Quiescent Current (mA)
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9.4 Device Functional Modes
9.4.1 Split-Supply and Single-Supply Operation
The OPA858 can be configured with single-sided supplies or split-supplies as shown in Figure 63. Split-supply
operation using balanced supplies with the input common-mode set to ground eases lab testing because most
signal generators, network analyzers, spectrum analyzers, and other lab equipment typically reference inputs and
outputs to ground. Split-supply operation is preferred in systems where the signals swing around ground.
However, the system requires two supply rails. In split-supply operation, the thermal pad must be connected to
the negative supply.
Newer systems use a single pow