Pure Sine-Wave Generator Circuit

  
A TTL counter, an 8-channel analog multiplexer, and a fourth-order low-pass filter can generate 10- to 25-kHz sine waves with a THD better than -80 dB. The circuit cascades the two second-order, continuous-time Sallen-Key filters within ICS to implement the fourth-order low-pass filter. To operate the circuit, choose the filter`s cutoff frequency,^, by tying IC3`s D0 through D6 inputs to-5 V or ground. The cutoff frequency can be at 128 possible levels between 1 and 25 kHz, depending on those seven digital input levels.Because the circuit ties D0 through D{, to ground Jc equals 1 kHz.
Pure Sine-Wave Generator Circuit - schematic

The 100-kQ potentiometer adjusts the output level between Vw - 1.5 V and Vss + 1.5 V.




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