Patent ID: 6628343
Filing Date: 2003-09-30
Classification: H04N

Abstract:
A television signal reception circuit, comprising an integrated circuit including:an automatic gain circuit for controlling a level of an input signal; first and second frequency mixture circuits to which an output of said automatic gain circuit is inputted; a &pgr;/2 phase shifting circuit for supplying local oscillation frequencies having a phase difference of &pgr;/2 from each other to said first and second frequency mixture circuits; a first &pgr;/4 phase shifting circuit for shifting a phase of an output of said first frequency mixture circuit by +&pgr;/4; a second &pgr;/4 phase shifting circuit for shifting a phase of an output of said second frequency mixture circuit by âˆ’&pgr;/4; and an addition circuit for adding outputs of said first and second &pgr;/4 phase shifting circuits; said television signal reception circuit outputting a television signal inputted to said integrated circuit through a variable frequency tuning circuit as an intermediate frequency signal, wherein said addition circuit is an equal amplitude addition circuit, comprising: a first differential amplification circuit for amplifying a first addition signal inputted thereto; a second differential amplification circuit for amplifying a second addition signal inputted thereto; first conversion means for converting an output of said first differential amplification circuit into a signal of a predetermined level in accordance with a control signal; second conversion means for converting an output if said second differential amplification circuit into a signal of a predetermined level in accordance with the control signal; detection means for detecting output levels of said first and second means; gain control means for generating the control signal in response to a detection signal of said detection means; and addition means for adding signals outputted form said first and second conversion means; the levels of the output signals of said first and second conversion means being controlled so as to be equal to each other in accordance with the control means signal outputted from said gain control means.