米6体育平台手机版

ZHCSOI9B July 2022 – December 2024 OPA817

PRODUCTION DATA

封装选项

请参考 PDF 数据表获取器件具体的封装图。

机械数据 (封装 | 引脚)

DTK|8

散热焊盘机械数据 (封装 | 引脚)

订购信息

8.2.1.2 Detailed Design Procedure

Input Impedance: The JFET-input stage of the OPA817 offers gigaohms of input impedance, and therefore enables the front-end to be terminated with a 1-MΩ resistor while achieving excellent precision. A 50-Ω resistance can also be switched in offering matched termination for high-frequency signals. The OPA817, therefore, enables the designer to use both 1-MΩ and 50-Ω termination in the same signal chain.
Noise: The total noise of the front-end amplifier is the function of the voltage and current noise of the OPA817, input termination, and the resistors thermal noise. In 50-Ω mode, the dominant noise source, however, is contributed by the voltage noise of the OPA817 as a result of noise being integrated over the complete bandwidth. Thus, the total RMS noise of the front-end amplifier is approximately equal to the voltage noise of OPA817 over 200 MHz.
The specified input referred voltage noise of the OPA817 is 4.5 nV/√Hz; see also Section 6.5. The total integrated RMS noise at the input in a bandwidth of 200 MHz is given by the following equation:
Equation 1. En_RMS = 4.5 nV/√Hz × √ (200 MHz × 1.57) = 80 µV_RMS.
The Brickwall correction factor of 1.57 is applied assuming the bandwidth is limited to 200 MHz with a single pole RC-filter before digitizing the signal with the ADC. Detailed calculations can be found at TI Precision Labs – Op Amps: Noise – Spectral Density.
Optimizing Overshoot: The OPA817 features an internal slew-boost circuit to deliver fast rise-time in applications needing high slew rates such as when configured as a transimpedance amplifier. For applications where overshoot needs to be limited, the input slew rates can be limited with introducing a series resistance (R_S) as shown in Figure 8-3. The resistance R_S forms a low pass filter with the input capacitance of approximately 2.6 pF at the noninverting pin of the OPA817 limiting the input slew rate to the amplifier. Figure 8-4 shows how limiting the input slew rate to the amplifier results in good overshoot performance, and Figure 8-5 shows how this achieves a small signal and large signal bandwidth of 200 MHz.