| 摘要 |
PROBLEM TO BE SOLVED: To provide a communication semiconductor integrated circuit (high-frequency IC) which is capable of making a capacitive element, which constitutes the output-side filter of a mixer circuit that down-converts the received signals, small in capacity without changing a cutoff frequency to turn the elements on-chip easily so as to decrease externally-attached elements in number. SOLUTION: A gilbert cell-type circuit is used as a mixer circuit 212 which compounds the received signals with local oscillation signals for down-converting, a low-pass filter which removes unnecessary waves from the output is composed of the load resistors Rc1 and Rc2 of upper differential transistors Q21, Q22 and Q23, Q24 and a capacitive element C1 between the differential output terminals, the load resistors Rc1 and Rc2 are increased in resistance value, a current circuit which applies a current to the emitters or collectors of the upper differential transistors Q21, Q2 and Q23, Q24 is provided, and a certain current corresponding to a current that is deceased by enlarging the load resistors Rc1 and Rc2 in resistance value is made to flow through a lower differential transistors Q11 and Q12. COPYRIGHT: (C)2007,JPO&INPIT
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