Simple Audio-Frequency Vco
Posted on Feb 7, 2013 12329
The frequency of this sine-wave oscillator is determined by a direct voltage, U` of 0 to 15 V. The distortion on
output signals of up to 10 Vpp is not greater than 1 o/o. When the output is reduced with the aid of P1 to 1 Vpp, the distortion drops to below 0.1 o/o. It is not recommended to use output signals below 1 Vpp, because the oscillator then becomes unstable and temperature-dependent. The oscillator consists of two operational transconductance amplifiers (OTAs) contained in one package. Their Amp-bias inputs, pins 1 and 16, are connected in parallel. These inputs can drive the output currents at pins 5 and 12 to a peak value of up to 0. 75 rnA. Switch S1 enables the oscillator output to be set to two ranges: 6. 7 to 400Hz and 400Hz to 23.8 kHz. The overall range needs a control voltage that varies from 1.34 to 15 V. When the frequency is changed by a variation of Uc and the setting of P1 is not altered, the output signal might be distorted. In other words, the amplitude of the signal must be adapted to the frequency.