| 摘要 |
A preamplifier is provided which couples a television tuner to a surface acoustic wave (SAW) filter and amplifies the I.F. signals supplied by the tuner so as to overcome the signal losses of the SAW filter. The preamplifier comprises a single transistor, the gain of which may be varied to provide desired gain and noise performance for the entire tuner-SAW filter-I.F. system. The gain of the preamplifier is simply adjusted by changing the values of one or two resistive components. The preamplifier includes a negative feedback path, which stabilizes the preamplifier against temperature variations, presents desired impedances to the tuner and SAW filter, and permits the substitution of a different transistor without the need for extensive readjustment. Means are provided for simply adjusting the biasing of the transistors without adversely affecting any previous gain adjustments. The biasing means also permits the most efficient operation of the preamplifier transistor by minimizing power dissipation and providing the highest available power handling capability in the preamplifier. The preamplifier may also include a tuned circuit which preshapes the I.F. signal response characteristic. The tuned circuit provides additional trapping of the adjacent channel sound signal, and an additional pole in the vicinity of the vestigial slope portion of the I.F. signal response characteristic.
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