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Voltage-controlled filter - Wikipedia, the free encyclopedia (170 words) |
 | A voltage-controlled filter (VCF) is a signal processing device in an analog synthesizer positioned after the oscillator. |
| A VCF is an example of an active non-linear filter: however, if its control voltage is kept constant, it will behave as a linear filter. |
| A VCF allows its cutoff frequency and Q factor to be continuously varied; it usually gives a lowpass response, but may also be switchable to allow highpass, bandpass or even notch responses. |
| Voltage-controlled filter - Patent 4039980 (3592 words) |
| It is convenient in a voltage curcuit (not shown) provided for generating the control voltage to indicate the cut-off frequency by a logarithmic indication and produce the control voltage logarithmically relative to the cut-off frequency, because this arrangement affords a wider range of variation in the cut-off frequency. |
| Accordingly, the base voltage of the npn transistors Tr.sub.4 and Tr.sub.5 are controlled by the control voltage applied to the terminal VC, and a sum of a potential of the resistor R.sub.5 to ground and the base-emitter voltage of the transistor Tr.sub.6 becomes the base voltage of the transistors Tr.sub.4 and Tr.sub.5. |
| The control voltage applied to the input terminal VQ is applied to the base of a transistor Tr.sub.10 and current corresponding to the control voltage flows through the emitter and the collector of the transistor Tr.sub.10. |
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