Abstract: A video circuit combines an audio-subcarrier notch filter, group-delay equalization, and an amplitude-adjustment capability for driving an RF video modulator in NTSC applications. The video circuit of Figure 1 combines an audio-subcarrier notch filter and group-delay equalization as required by the ITU-470 standard. The circuit also includes amplitude-adjustment capability for driving an RF video modulator in NTSC applications. (PAL operation requires a minor adjustment of the filter and allpass values.) Figure 1. Bandstop filter and delay equalizer for NTSC applications. For best performance, the input should be driven from a low-impedance source such as an op amp or active filter. Two second-order allpass stages (U1a, R1, C1, L1) and (U1c, R13, C3, L3) and a first-order allpass stage (U1d, C4, R14) form a fifth-order group-delay equalizer that compensates for group delay introduced by the notch filter (U1b, R6, C2, L2). See Figure 2. Potentiometer R7 adjusts the output amplitude as required by the modulator in use. Figure 2. Gain and group-delay response for the notch filter and group-delay compensation of Figure 1. The notch frequency is set by L2 and C2; the notch depth and bandwidth are set by R4, R5, and R6. The typical notch depth is greater than -16dB. Flatness above 2.5MHz is ±0.5dB. A similar article appeared as a Design Brief in the July 21, 2005 issue of Electronic Design. 相关型号   APP 3745: Mar 13, 2006 MAX4383 超小型、低成本、210MHz、单电源运算放大器，带有满摆幅输出及禁止功能 完整的数据资料 (PDF, 760kB) 免费样品 自动更新 需要自动接收最新发布的应用笔记吗？请订阅EE-Mail™ (English only)。 我们期待您的反馈！ 喜欢？不喜欢？有待改善？或为我们提供建议？请与我们联系 — 我们将根据您的意见或建议改善我们的工作。 网页评价或提供建议   下载，PDF格式 (42kB)  AN3745, AN 3745, APP3745, Appnote3745, Appnote 3745