Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reissue Patent
1999-02-24
2001-06-12
Mottola, Steven J. (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
C330S264000
Reissue Patent
active
RE037217
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an operational amplifier, and more particularly, to an operational amplifier having an output section constituted by a push-pull circuit.
Further, the present invention also relates to a current detector circuit and an amplifier employing the current detector circuit, and more particularly, to a current detector circuit for selecting a smaller one from current values (two current values) of a current flowing through a detecting object (detecting device) and maintain the current flowing through the detecting object at a predetermined value and an amplifier employing the current detector circuit, capable of operating with a low source voltage.
2. Description of the Related Art
Recently, compact and low-power-consumption electronic apparatuses have been developed. Portable electronic devices are mostly driven by batteries. Homeuse and office-use electronic apparatuses driven by, for example, AC 100 (117, 200, or 220) V usually employ semiconductor integrated circuits (LSIs) operating with a power source voltage of 5 V.
The portable devices driven by battery, however, usually operate with a power source voltage of 3 V. The battery voltage decreases as the battery wares. LSIs in the portable devices must deal with such a fluctuation in the source voltage and a variety of source voltages ranging from 3 to 5 V. Namely, the LSIs must be stable for a wide range of source voltages.
To let an analog circuit operate for a wide range of source voltages, an operational amplifier plays an important role. An operational amplifier whose output section constituted by a push-pull circuit may be used for heavy load or a high-speed operation in an analog-digital mixed signal LSI consisting of CMOSs. In this case, the operational amplifier must be particularly stable. It is required to provide an operational amplifier that shows stable performance for a wide range of source voltages.
By the way, low-frequency amplifiers are classified into classes A, B, and AB. The A-class amplifiers involve a low signal distortion but large power consumption. The B-class amplifiers involve a large signal distortion but small power consumption. The AB-class amplifiers involve a small signal distortion and small power consumption.
Amplifiers for driving speakers must provide a large current at low distortion. For this purpose, the A-class amplifiers consume large power even when there are no signals, and the B-class amplifiers cause a problem of crossover. Accordingly, the AB-class amplifiers are usually employed to drive speakers.
To reduce power consumption low-voltage power source are widely used. It is necessary, therefore, to develop amplifiers operating with a low-voltage power source.
SUMMARY OF THE INVENTION
An object of a first aspect of the present invention is to provide an operational amplifier that operates stably for a wide range of source voltages. An object of a second aspect of the present invention is to provide a current detector circuit for selecting a smaller one from current values of a current flowing through a detecting object (detection device) and control the current to a predetermined value, as well as providing an amplifier employing the current detector circuit, to operate with a low-voltage power source.
According to a first aspect of the present invention, there is provided an operational amplifier comprising a differential amplification section; an output section having a first transistor of a first conductivity type and a second transistor of a second conductivity type that is opposite to the first conductivity type, the first and second transistors being connected in series between a first power source unit and a second power source unit, the first transistor being driven according to an output of the differential amplification section; a control signal generation unit for detecting a current flowing through the first transistor and generating a control signal in response to the detected current; and a drive control unit for driving the second transistor in response to the control signal.
The drive control unit may control the second transistor to increase a current flowing through the second transistor if the current flowing through the first transistor detected by the control signal generation unit decreases. The control signal generation unit may have a third transistor of the first conductivity type having a first terminal connected to the first power source and a control terminal connected to the output of the differential amplification section as well as to the control terminal of the first transistor; and the drive control unit may have fourth and fifth transistors of the first conductivity type having first terminals connected to the first power source unit, a sixth transistor of the second conductivity type having a first terminal connected to the second power source unit and a control terminal and a second terminal connected to the second terminal of the fifth transistor as well as to the control terminal of the second transistor, and a constant current source, the control terminal and second terminal of the fourth transistor being connected to the second power source unit through the constant current source, to the control terminal of the fifth transistor, and to the second terminal of the third transistor, to receive the control signal from the control signal generation unit. The first transistor may be connected to the third transistor in a current mirror configuration, the fourth transistor may be connected to the fifth transistor in a current mirror configuration, and the second transistor may be connected to the sixth transistor in a current mirror configuration.
The control signal generation unit may have a third transistor of a first conductivity type having a first terminal connected to the first power source unit and a control terminal connected to the output of the differential amplification section as well as to the control terminal of the first transistor; and the drive control unit may have fourth, fifth, and sixth transistor of the second conductivity type having first terminals connected to the second power source unit, and a constant current source, the second terminal of the fifth transistor, the second terminal and control terminal of the sixth transistor, and the control terminal of the second transistor being connected to the first power source unit through the constant current source, the second terminal and control terminal of the fourth transistor and the control terminal of the fifth transistor being connected to the second terminal of the third transistor, to receive the control signal from the control signal generation unit. The first transistor may be connected to the third transistor in a current mirror configuration, the fourth transistor may be connected to the fifth transistor in a current mirror configuration, and the second transistor may be connected to the sixth transistor in a current mirror configuration.
The drive control unit may control the second transistor to pass a current if a current flowing through the first transistor detected by the control signal generation unit is larger than a predetermined value. The control signal generation unit may have a third terminal connected to the first conductivity type having a first terminal connected to the first power source unit and a control terminal connected to the output of the differential amplification section as well as to the control terminal of the first transistor; and the drive control unit may have a load unit, a fourth transistor of the first conductivity type having a first terminal connected to the control terminal of the first transistor as well as to the control terminal of the third transistor and a second terminal connected to the control terminal of the second transistor as well as to the second power source unit through the load unit, and a first constant current source, the second terminal of the third transistor and the control terminal of the fourth transistor being connected to
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
Mottola Steven J.
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