| 摘要 |
1276342 Transistor circuits; radio receiving circuits RCA CORPORATION 29 Aug 1969 [30 Aug 1968] 43058/69 Headings H3Q and H3T In a parallel resonant circuit, tuned over a band by means of a varactor diode, the bandwidth is maintained constant over the tuning range; the circuit comprising inductor 2P and capacitor 30, Fig. 2b, is chamfered by means of resistor 34 in series with inductor 32 which are so proportional that the parallel damping thrown on the tuned circuit is substantially proportional to the square of the frequency. The tuned circuit may be shunted by two such series connected inductors and resistances (Fig. 2a, not shown) the one resistance being that of the signal source and the other that of the load. As applied to a VHF television tuner, the aerial terminal 62, Fig. 1, is coupled to the emitter of a common-base transistor RF amplifier 84 via a tuning circuit comprising series inductors 64, 66 and parallel tuned circuit 68,70 in series with an I.F. rejection circuit 78, 80, 81. The collector, of transistor 84 is coupled to the base of a second transistor RF amplifier 86, in common emitter connection, via a high-frequency peaking circuit 98, 100, 102, 104. The collector of transistor 86 feeds into the emitter of transistor 172, acting as a frequency-changer in common base connection, via a circuit comprising seriesconnected inductors 122, 124, loading resistor 114 and the tuned circuit 126, 128. An I.F. output is taken from the collector of transistor 172 via transformer 180. Transistor 136 comprises the local oscillator, its base being earthed for R.F. by feed-through capacitor 166 and its emitter connected to a tap on inductor 138, which in conjunction with varactor diode 144 forms a tuned collector circuit. Local oscillations are fed to the emitter of mixer 172 via capacitor 168 and inductor 170. |
