Automobile tuner system

A receiver comprising:

• a first converter for performing frequency conversion on one of an FM signal to be used for a keyless entry system and a high frequency signal of FM broadcast;
• an IF limiter amplifier for amplifying an output signal of said first converter and subsequently limiting an amplitude of the output signal to a predetermined level;
• a second converter for performing frequency conversion on a high frequency signal of AM broadcast;
• an IF amplifier provided with an AGC function for amplifying an output signal of said second converter;
• an AM detector circuit for AM-detection;
• a selector for applying one of an output signal of said IF limiter amplifier and an output signal said IF amplifier;
• and
• a microcomputer for controlling the operation of locking and unlocking a door of an automobile on the basis of an AM keyless signal output from said AM detector circuit;
• wherein said selector selects the output signal of said IF limiter amplifier when said first converter performs frequency conversion on the AM signal and selects the output signal of said IF amplifier when said first converter performs frequency conversion on the high frequency signal for FM broadcast,
• and the AM broadcast generated on the basis of an AM radio signal output from said AM detector circuit.

A receiver comprising:

• an FM tuner having an FM mixer for converting the frequency of an FM signal;
• a double conversion type AM tuner having a first AM mixer for up-converting the frequency of an AM signal and down-converting the frequency of the AM signal;
• and
• a PLL circuit having a crystal oscillator, a first VCO for generating an output signal to be applied to said FM mixer on the basis of the outcome of comparing the output signal of said crystal oscillator and that of said FM mixer and a second VCO for generating an output signal to be applied to said first AM mixer on the basis of the outcome of comparing the output signal of said crystal oscillator and that of said first AM mixer;
• wherein said crystal oscillator includes a first oscillation circuit, a second oscillation circuit having a loop gain higher than the first oscillation circuit and a control circuit for activating at least said second oscillation circuit for a predetermined period of time after the start and inactivating said second oscillation circuit after the predetermined period of time, while keeping said first oscillation circuit activated;
• the output terminals of said first and second oscillation circuits being connected commonly and positively fed back.