The circuit of Figure 1 produces an accurate variable-frequency sine wave for use as a general-purpose reference signal. It includes an 8th-order elliptic, switched-capacitor lowpass filter (IC3) that is clocked with a 100kHz square wave generated by microcontroller IC2. (Any other convenient squarewave source is also acceptable.) The microcontroller is clocked by a 10MHz oscillator module. A voltage supervisor (IC1) ensures correct operation in the event of a power failure. IC3 sets the filter's cutoff frequency at 1/100 the clock frequency. Figure 1. By removing harmonics from a square wave, this circuit generates an accurate and adjustable sine-wave output. The 8th-order elliptic filter's sharp rolloff sharply reduces the harmonic amplitudes in a 1kHz square-wave input, thereby producing a near-perfect 1kHz sine wave at its output. Using divider-chain logic or a processor, you can then create a digitally adjustable sine-wave source by adjusting the clock and input frequencies while maintaining a ratio of 100:1 between them. For the microcontroller shown, software to implement this idea is available for download. (.asm, 4K) To prevent clipping at the positive and negative peaks, attenuate the input signal and superimpose it on a dc level of VCC/2. The result (for a 5V input) is a 2.25V peak-to-peak output. A similar version of this article appeared in the May 15, 2003 issue of EDN magazine. 相关型号   APP 2081: Jun 27, 2003 MAX7400 八阶、低通、椭圆函数、开关电容滤波器 完整的数据资料 (PDF, 200kB) 免费样品 MAX809 3引脚微处理器复位电路 完整的数据资料 (PDF, 208kB) 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 (24kB)  AN2081, AN 2081, APP2081, Appnote2081, Appnote 2081