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Voice Bandwidth Filter(TL072)

2015-01-16 18:44  
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This article describes the Voice Bandwidth Filter (TL072). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: TL072.

This circuit passes frequencies in the 300Hz – 3.1kHz range, as present in human speech. The circuit consists of cascaded high-pass and low-pass filters, which together form a complete band-pass filter. One half of a TL072 dual op amp (IC1a) together with two capacitors and two resistors make up a second-order Sallen-Key high-pass filter. With the values shown, the cut-off frequency (3dB point) is around 300Hz. As the op amp is powered from a single supply rail, two 10kO resistors and a 10μF decoupling capacitor are used to bias the input (pin 5) to one-half supply rail voltage.

Circuit diagram:

Figure:1 Voice Bandwidth Filter Circuit Diagram

Figure 1 Voice Bandwidth Filter Circuit Diagram

The output of IC1a is fed into the second half of the op amp (IC1b), also configured as a Sallen-Key filter. However, this time a low-pass function is performed, with a cut-off frequency of about 3.1kHz. The filter component values were chosen for Butterworth response characteristics, providing maximum pass-band flatness. Overall voltage gain in the pass-band is unity (0dB), with maximum input signal level before clipping being approximately 3.5VRMS. The 560O resistor at IC1b’s output provides short-circuit protection.



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