Patent ID: 6160572
Filing Date: 2000-12-12
Classification: H03J,H03K

Abstract:
A tuner for a cable modem connected to an upstream side and a downstream side of a CATV station, comprising:upstream circuit means for transmitting data to said upstream side;filter means connected to said downstream side for removing data for said upstream side;selecting means for dividing into at least two groups and selectively outputting input signals having different frequencies received from an output of said filter means, on frequency band basis;at least two radio frequency tuning means for said at least two groups for tuning to predetermined frequency and amplifying each group of the received signals selected by said selecting means;at least two frequency converting means for said at least two groups for converting an output signal from each of said radio frequency tuning means to an intermediate frequency signal;intermediate frequency amplifying means for amplifying the signal of which frequency is converted by each of said frequency converting means;each of said radio frequency tuning means includes;radio frequency input tuning means for tuning the received signals selected by said selecting means to a predetermined frequency,radio frequency amplifying means for amplifying an output signal from said radio frequency input tuning means, andradio frequency output tuning means for tuning an output signal from said radio frequency amplifying means to a predetermined frequency;said selecting means selectively outputs two groups of received signals belonging, of a first frequency band, a second frequency band having higher frequency than said first frequency band and a third frequency band having higher frequency than said first and second frequency bands, to said first and second frequency bands, and to signal based on the local oscillation signal generated by said local oscillation means; andthe radio frequency input tuning means for said third frequency band includesa tuning circuit including a high pass filter, a tuning coil, a variable capacitance element for tuning and a tuning voltage applying circuit for applying a tuning voltage to the variable capacitance element for tuning,a variable capacitance element for impedance matching, andbias means for supplying a bias voltage to the radio frequency amplifying means of a succeeding stage through a resistor;wherein said variable capacitance element including parallel-connected variable capacitance diodes of identical characteristics connected in series to parallel-connected variable capacitance diodes in opposite directions.