Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
1999-04-20
2001-03-27
Lee, Benny (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
C330S267000
Reexamination Certificate
active
06208208
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an operational amplifier method and an operational amplifier. It specifically relates to an operational amplifier circuit with a low dissipation current and a large drive current, which is powered by a low voltage power supply.
2. Description of the Related Art
Recently, to embed in a system LSI (Large Scale Integrated circuit) for a portable apparatus such as an electronic notebook or a digital watch, powered by a primary battery, the CMOS (Complementary Metal Oxide Semiconductor) operational amplifier circuit (which has been made up using a CMOS manufacturing process) is frequently utilized.
These portable devices driven by the battery have to function with dissipation currents ranging from several microamperes to several milliamperes with the help of a power supply voltage of 1.5 volts or less. Accordingly, an operational amplifier circuit, where functions are powered by a low power supply voltage with a low dissipation current, is required.
In addition, an operational amplifier circuit with a high output capability as well as a capability of operating with a low dissipation current, powered by a low voltage supplied by a power supply, is also in demand for a portable apparatus. It is desired, for example, to further decrease a dissipation current spent in a portable apparatus during its steady-state operation, and drive a loudspeaker via the operational amplifier circuit by the output of a D/A (Digital to Analog) converter, which along with an A/D (Analog to digital) converter has been embedded on the same chip as the operational amplifier circuit.
To respond to the request, a folded cascode-type operational amplifier circuit
700
(hereafter, referred to as just “operational amplifier circuit”) as shown in
FIG. 1
has been proposed.
The operational amplifier circuit
700
is comprised of: a folded cascode-type operational amplifier circuit
71
including n-channel transistors
74
and
75
which make up a pair of differential transistors and a current mirror circuit
76
. Also included is push-pull output circuit
72
including a p-channel output transistor
77
, a n-channel output transistor
78
, a condenser for phase compensation Cc, and an output terminal
79
. A bias circuit
73
supplies the folded cascade circuit
71
and the push-pull output circuit
72
with a bias voltage.
Upon application of an input signal to gates G
74
and G
75
of the n-channel transistors
74
and
75
which make up a pair of differential transistors, a signal amplified by the folded cascode circuit
71
is output to a common gate terminal A of the current mirror circuit
76
and an output terminal B of the folded cascode circuit
1
, amplified by the p-channel output transistor
77
and the n-channel output transistor
78
, and output to the output terminal
79
.
The conventional operational amplifier
700
as described above has a feature where: the range of input voltages is wide; the range of output voltages is extended to the earth voltage; and it is possible to function with the help of a low voltage of 1 volt or less supplied by a power supply.
However, the operational amplifier circuit
700
is not configured in such a manner that the p-channel output transistor
77
is driven by the output of the differential amplifier circuit. In addition, it also does not comprise a circuit configuration used in setting an idling current for the n-channel output transistor
78
.
Thus, there is a shortcoming with the operational amplifier circuit
700
where the push-pull output circuit
72
operates as a class A amplifier so that the maximum output current of the operational amplifier circuit
700
is limited to an amount which is equal to or less than the idling current flowing through the p-channel output transistor
77
.
Furthermore, when the push-pull output circuit
72
operates and outputs a high amplitude of signal, the shape of the high amplitude of signal is asymmetric with respect to the middle point of voltage. This causes an increase in an odd-order harmonic distortion.
SUMMARY OF THE INVENTION
Accordingly, the objective of the present invention is to provide an operational amplifier method and an operational amplifier, powered by a low voltage power supply such as a dry element cell, which operates with a low dissipation current and a high drive capability.
To attain the above objective, an operationally amplifying method according to an aspect of the present invention is provided comprising: a first amplifying step (S
4
) of amplifying an input signal in a class A amplification mode when the input signal is small; and a second amplifying step (S
5
) of amplifying an input signal in a class B amplification mode when the input signal is large. An embodiment according to this method is shown in FIG.
8
.
According to another aspect of the present invention, an operational amplifier is provided comprising: an amplifier (
1
) which amplifies an input signal; an idling current provider (
2
) which provides a constant current; and a driver (
104
,
204
) which outputs a output signal in accordance with the sum of the input signal amplified by the amplifier (
1
) and the constant current provided by the idling current provider (
2
), wherein, the driver (
104
,
204
) functions in a class A amplification mode when the input signal is small, otherwise, it functions in a class B amplification mode when the input signal is not small. Embodiments according to the above invention are shown in FIGS,
2
,
3
,
6
, and
7
.
REFERENCES:
patent: 4015212 (1977-03-01), Miyata
patent: 4135162 (1979-01-01), Takahashi
patent: 5754078 (1998-05-01), Tamagawa
patent: 5789980 (1998-08-01), Nagata et al.
patent: 6005440 (1999-12-01), Okamoto
patent: 62-82704 (1987-04-01), None
patent: 5-95231 (1993-04-01), None
Japanese Office Action issued Sep. 12, 2000 in a related application with English translation of relevant portions.
Komatsu Yuji
Taguchi Yasuhiro
Yukawa Akira
Choe Henry
Lee Benny
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
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