| 摘要 |
A television (TV) receiver tuning system for selecting one of a plurality of receivable TV channels comprises a frequency selective radio frequency device including trimming elements for receiving TV signals, a local oscillator controlled by a first control signal and a mixer in which the TV signals and the local oscillator signal are heterodyned to develop an intermediate frequency signal. A first control device develops the first control signal in response to the selection of a TV channel to control the local oscillator frequency so that the mixer shifts the selected TV channel signal to the IF frequency. A second control device including a PROM trims the frequency selectivity of the RF device using its trimming elements unaffected by selection of the TV channel whereby mechanical alignment of the TV tuning system can be avoided. In other aspects of the invention, the second control device develops signals for adjusting tunable circuits in the IF amplifier, for adjusting the tracking of the local oscillator frequency in relation to its control signal, and, in a double-conversion tuner, for adjusting the frequency of a second local oscillator. |
