Amplifier, filter using the same, and radio communication device

Abstract

An amplifier includes an amplification unit which amplify a first difference between first and second input signals, a second difference between second and third input signals and a third difference between third and first input signals by a differential mode gain, and amplify an average of the first, second and third input signal by a common mode gain, for outputting a first output signal corresponding to a sum of the amplified first difference and the amplified average, a second output signal corresponding to a sum of the amplified second difference and the amplified average, and a third output signal corresponding to a sum of the amplified third difference and amplified average; first, second; and a reduction circuit which reduces the common mode gain less than the differential mode gain.

1 . An amplifier comprising:
 a first input terminal which inputs first input signal;   a second input terminal which inputs second input signal;   a third input terminal which inputs third input signal;   an amplification unit configured to amplify the first input signal, second input signal, and third input signal by a differential mode gain and a common mode gain to output a first output signal, a second output signal, and a third output signal;   a first output terminal which outputs the first output signal;   a second output terminal which outputs the second output signal;   a third output terminal which outputs the third output signal; and   a setting circuit configured to set the common mode gain less than the differential mode gain,   wherein the amplification unit includes first, second, and third transistors including control terminals connected to the first, second, and third input terminals, respectively, first main terminals connected to the first, second, and third output terminals, respectively, and a common second main terminal; and first, second, and third load resistors connected to the first main terminals of the first, second, and third transistors, respectively,   the common mode gain has a value close to 0, and   the differential mode gain is given by a product gmR of the transconductance gm of the first, second, and third transistors and the resistance R of the load resistors.   
   
   
       2 . A filter comprising:
 the amplifier according to  claim 1 ; and   a time constant circuit including: fourth, fifth, and sixth input terminals which receive fourth, fifth, and sixth input signals, respectively; and a plurality of resistors and a plurality of capacitors connected between the first, second, and third input terminals and the fourth, fifth, and sixth input terminals and between the first, second, and third input terminals and the first, second, and third output terminals.   
   
   
       3 . A radio communication device comprising:
 a receiver which receives a radio frequency signal;   a demodulator which demodulates an output signal from the receiver in order to generate first, second, and third baseband signals;   the amplifier according to  claim 1  which receives the first, second, and third baseband signals and which amplifies the first, second, and third baseband signals in order to output first, second, and third output baseband signals;   an analog-to-digital converter which converts the first, second, and third output baseband signals into digital baseband signals; and   a processing unit configured to receive the digital baseband signals and perform processing for decoding.   
   
   
       4 . A radio communication device comprising:
 a processing unit configured to process data to be transmitted in order to generate first, second, and third digital baseband signals;   a digital-to-analog converter which converts the first, second, and third digital baseband signals into first, second, and third analog baseband signals;   the amplifier according to  claim 1  which receives the first, second, and third analog baseband signals and which amplifies the first, second, and third baseband signals in order to output first, second, and third output baseband signals;   a modulator which modulates the first, second, and third output baseband signals in order to output a radio frequency signal; and   a transmitter which transmits the radio frequency signal.