Low-Frequency Lc Oscillator

I ¬?I 1 I LOW-FREQUENCY LC OSCILLATOR It is not always appreciated that LC cir- cuits may be used for generating low frequencies. The proposed circuit, pro- vided it uses good-quality components, can be used for frequencies down to 150 Hz, and possibly even slightly lower. The oscillator proper consists of Ti and Ta with the LC circuit connected in the collector circuit of T2. The amplification is set with the aid of the current source around Ts. The voltage across the tuned circuit is tapped at high impedance and amplified by Ts. The output of this FET is buffered by T3 and then rectified by Di-Da. The resulting direct voltage is used for driving the current source. Since the rectified voltage still contains a ripple, a further buffer, T4, is added at the output of the circuit. The circuit draws a current of about 20 mA, which can rise to about 25 mA at higher frequencies. Its output im- pedance has been kept as low as poss- ible to render the bandwidth of the os- cillator as b...