本文的类似版本刊登在 2003 年 5 月 15 日的《EDN》杂志上。图 1 中的电路可产生精确的变频正弦波，用作通用参考信号。它包括一个 8 阶椭圆开关电容低通滤波器 (IC3)，该滤波器的时钟由微控制器 IC2 产生的 100kHz 方波提供。（任何其他方便的方波源也可以接受。）微控制器的时钟由 10MHz 振荡器模块提供。电压监控器 (IC1) 确保在电源故障时正常运行。IC3 将滤波器的截止频率设置为时钟频率的 1/100。图 1。通过从方波中去除谐波，该电路可产生精确且可调节的正弦波输出。8 阶椭圆滤波器的急剧下降急剧降低了 1kHz 方波输入中的谐波幅度，从而在其输出端产生近乎完美的 1kHz 正弦波。然后，使用分频器链逻辑或处理器，您可以通过调整时钟和输入频率来创建数字可调正弦波源，同时保持它们之间的比率为 100:1。为了防止在正峰值和负峰值处削波，请衰减输入信号并将其叠加在 VCC/2 的直流电平上。结果（对于 5V 输入）是 2.25V 峰峰值输出。

A similar version of this article appeared in the May 15, 2003 issue of EDN magazine.

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.

To prevent clipping at the positive and negative peaks, attenuate the input signal and superimpose it on a dc level of V_CC/2. The result (for a 5V input) is a 2.25V peak-to-peak output.