Generators with a stable amplitude. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer
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The harmonic signal generator (Fig. 1) with frequencies from 10 Hz to 100 kHz has a high amplitude stability.
Ris.1
The stabilization of the signal amplitude is carried out using a field-effect transistor included in the POS circuit. The field effect transistor is controlled by a constant voltage, which is formed on the capacitor C1 and amplified by the op-amp DA2. The large transfer coefficient of the op amp DA2 holds the amplitude of the harmonic signal with an accuracy of tens of millivolts in the range from 1 to 9 V. The amplitude is adjusted by the potentiometer R9. The harmonic content of the output signal is less than 0,1%.
Signal amplitude stabilization with LEDs
The gain of the op-amp (Fig. 2) is set using resistors R3 and R4 and is equal to 3,2. This gain is needed to start the generator. As soon as the amplitude of the harmonic signal increases to 1,6 V, the diodes open and an additional OOS circuit appears.
Ris.2
The gain drops and the amplitude of the harmonic oscillation stabilizes at a certain level. The distortions introduced by the stabilization circuit do not exceed 1%. The amplitude of the output signal is adjustable from 2 to 5V. The frequency depends on the elements of the Wien bridge and can take values from units of hertz to hundreds of kilohertz.
Generator with automatic signal amplitude control
The generator (Fig. 3) is assembled on a VT1 field-effect transistor with a double T-shaped bridge in the OS circuit. To stabilize the amplitude of the output signal in the collectors of transistors VT2 and VT3, the oscillations are rectified by a detector assembled on elements C6, C7, VD1, VD2. At the output of the detector, a constant voltage of positive polarity is formed. When there are no oscillations in the generator, a current flows through the resistor R11, opening the transistor UT4.
Ris.3
Resistor R8 is included in the source circuit of the field-effect transistor. The resistance of this resistor sets such a current through the transistor VT1, at which its steepness is maximum. When generating, the voltage from the detector closes VT4, reducing the steepness of VT1 and thereby stabilizing the amplitude of the generator. The frequency of generated oscillations is 1 kHz.
To increase or decrease the frequency of the output signal, it is necessary to proportionally change the values of the elements R1-R3, C2-C4. By changing the ratio of resistors R10 and R11, you can change the amplitude of the output signal.
Publication: N. Bolshakov, rf.atnn.ru
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