| 摘要 |
1,250,919. Transistor oscillator circuits; key senders. WESTERN ELECTRIC CO. Inc. 7 July, 1969 [8 July, 1968], No. 34120/69. Headings H3T and H4K. A transistor oscillator Q1, Q2, Q3, Q4 and TTF, for a telephone key sender, stabilized against variations in temperature and supply voltage, includes a phase-shifting network TTF containing only R and C components and preferably being a Twin Tee filter, and also a negative feedback circuit Q1A, R2, R1, Q2A, which for example limits the peaks of half cycles of one polarity (Fig. 2B, not shown) by providing a negative feedback path during those half cycles. In operation, one of an array of push buttons PB is pressed, inserting corresponding components into Twin Tee filter to produce a burst of oscillation from a high frequency oscillator and a low frequency oscillator, each oscillation having one of four values of frequency determined by the components inserted into the corresponding Twin Tee. On positive half cycles at the base of Q5, Q1A and Q2A are turned on, thus providing a negative feedback path, to limit the peaks of the half cycles by lowering the voltage at the base of Q3. The circuit is integrated and temperature effects in the limiting circuit are eliminated by forming R2 of silicon, having a positive temperature coefficient, and R1 of tantalum having a negative temperature coefficient. The effect of loop length is minimized by making the collector currents of Q1 and Q1A equal. |
