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US 7,398,070 B2Granted
Variable gain amplifying circuit with matchable input/output impedance
AssigneeAlps Electronic Co., Ltd.
InventorsMasaki Yamamoto, Masaaki Endo
Life of this patent
Estimating the term…
Abstract
A variable gain amplifying circuit includes a gate-grounded amplifying FET and a collector-grounded amplifying transistor. A gate voltage of the FET and a base voltage of the transistor are adjusted by a supplied AGC voltage. When an input RF signal has small amplitude, the gate voltage is increased by a high AGC voltage so as to increase a main current of the FET, thereby increasing a signal gain of the FET. When the input RF signal has large or medium amplitude, the gate voltage is decreased by a low AGC voltage so as to decrease a main current of the FET, thereby decreasing the signal gain of the FET.
Claims8
A variable gain amplifying circuit comprising:
- a semiconductor amplifying stage using a semiconductor amplifying device having a control electrode, a first main electrode, and a second main electrode having a low output impedance characteristic,
- wherein, in the semiconductor amplifying device, an RF signal is input to the control electrode and a bias circuit for generating a bias voltage is connected to the control electrode, the first main electrode is alternately grounded, and an amplified RF signal is output from the second main electrode, and
- wherein the bias circuit adjusts the bias voltage of the control electrode corresponding to a supplied AGC voltage, and as the amplitude of the input RF signal becomes large, the bias voltage of the control electrode decreases and a main current flowing through the first main electrode and the second main electrode decreases to thereby decrease a signal gain of the semiconductor amplifying device, but as the amplitude of the input RF signal becomes small, the bias voltage of the control electrode increases and the main current increases to thereby increase the signal gain of the semiconductor amplifying device.
A variable gain amplifying circuit comprising:
- a semiconductor amplifying stage using first and second semiconductor amplifying devices, each having a control electrode, a first main electrode, and a second main electrode having a low output impedance characteristic,
- wherein, in the first semiconductor amplifying device, the control electrode is alternately grounded and a first bias circuit for generating a bias voltage is connected to the control electrode, an RF signal is input to the second main electrode, and an amplified RF signal is output from the first main electrode, and in the second semiconductor amplifying device, the RF signal output from the first semiconductor amplifying device is input to the control electrode and a second bias circuit for generating a bias voltage is connected to the control electrode, the first main electrode is alternately grounded, and an amplified RF signal is output from the second main electrode,
- wherein the first and second bias circuits adjust the bias voltages of the control electrodes, respectively, corresponding to a supplied AGC voltage, and as the amplitude of the input RF signal becomes large, the bias voltage supplied to the control electrode of the first semiconductor amplifying device decreases and a main current flowing through the first main electrode and the second main electrode of the first semiconductor amplifying device decreases to thereby decrease a signal gain of the first semiconductor amplifying device, but as the amplitude of the input RF signal becomes small, the bias voltage of the control electrode of the first semiconductor amplifying device increases and the main current increases to thereby increase the signal gain of the semiconductor amplifying device, and
- wherein, as the amplitude of the input RF signal becomes large, the bias voltage supplied to the control electrode of the second semiconductor amplifying device increases and a main current flowing through the first main electrode and the second main electrode of the second semiconductor amplifying device increases, but as the amplitude of the input RF signal becomes small, the bias voltage of the control electrode of the second semiconductor amplifying device decreases and the main current decreases.
1 more element
Dependencies are inferred from the claim text.