Amplifiers – With semiconductor amplifying device – Including frequency-responsive means in the signal...
Reexamination Certificate
2002-12-04
2004-07-27
Mottola, Steven J. (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including frequency-responsive means in the signal...
C330S286000
Reexamination Certificate
active
06768383
ABSTRACT:
THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCT INTERNATIONAL APPLICATION PCT/JP01/10993.
TECHNICAL FIELD
The present invention relates to a high-frequency amplifier for use in a communications device such as a mobile telephone.
BACKGROUND ART
A conventional high-frequency amplifier shown in
FIG. 14
generally includes a transmission line
1403
having one end connected between an amplifier circuit
1401
and an output matching circuit
1402
and the other end connected to a power source
1405
and is grounded via a capacitor
1404
.
The transmission line
1403
is designed to have ¼ the wavelength of a frequency band of a signal be amplified by the amplifier circuit
1401
. The capacitance of the capacitor
1404
is set to a level great enough to short-circuit in the frequency band.
A bias current received from the power source
1405
is a direct current and thus does not flow through the capacitor
1404
but flows through the transmission line
1403
to drive the amplifier circuit
1401
. The amplifier circuit
1401
amplifies a signal in the frequency band and may simultaneously generate harmonic distortions in a band of n times greater than the frequency band (where n is an integer). The capacitor
1404
is short-circuited in the frequency band and the length of the transmission line
1403
is equal to ¼ the wavelength. As a result, the transmission line
1403
is inverted in phase at one end and stays open, thus allowing the amplified signal to be received not by a bias circuit
1406
but by the output matching circuit
1402
.
In the frequency band of 2n times greater than the band, the capacitor
1404
is short-circuited. Also, the length of the transmission line
1403
is equal to ½ the wavelength. Therefore, the bias circuit
1406
functions as a notch circuit. As a result, the harmonic distortions at 2n times the frequency band can be attenuated and hardly received by the output matching circuit
1402
.
FIG. 15
illustrates a frequency response of a conventional high-frequency amplifier including an amplifier circuit
1401
having an output impedance of 3.2-j5.7&OHgr; in an output frequency band of 900MHz.
Since the bias circuit of the conventional high-frequency amplifier develops an insufficient short-circuit across the capacitor at the frequencies of second and third harmonics, a low pass filter needs to be connected after the matching circuit for attenuating the harmonic distortions. This increases the overall size of the circuit, and reduces the operating efficiency of the conventional high-frequency amplifier due to a loss of the added low pass filter; thus increasing current consumption for producing a desired level of power.
SUMMARY OF THE INVENTION
A high-frequency amplifier includes (a) an amplifier circuit, (b) an output matching circuit, and (c) a bias circuit. The bias circuit includes a parallel circuit constructed by a first capacitor and a first transmission line having a first end connected between the amplifier circuit and the output matching circuit and a second end connected to a power source, and a second capacitor having a first end connected to a second end of the parallel circuit and a second end grounded.
While remaining open in a frequency band of a signal to be amplified by the amplifier, the bias circuit is short-circuited in a desired frequency band. This allows undesired harmonic distortions in the signal to be attenuated without using a low pass filter.
REFERENCES:
patent: 5105172 (1992-04-01), Khatibzadeh et al.
patent: 6177841 (2001-01-01), Ohta et al.
patent: 6373331 (2002-04-01), Smiley et al.
patent: 06-140862 (1994-05-01), None
patent: 11-205052 (1999-07-01), None
Japanese search report for PCT/JP01/10993 dated Dec. 14, 2001.
English translation of Form PCT/ISA/210.
Kato Hisayoshi
Kushitani Hiroshi
Tsuneoka Michiaki
Mottola Steven J.
RatnerPrestia
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