Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – With specific source of supply or bias voltage
Reexamination Certificate
1999-11-03
2001-08-14
Ton, My-Trang Nu (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
With specific source of supply or bias voltage
C327S560000
Reexamination Certificate
active
06275095
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a semiconductor amplifier circuit and, particularly, to a semiconductor amplifier circuit such as an operational amplifier circuit driven by a positive and negative power source or a push-pull driven amplifier circuit having an output potential intermediate between a ground potential and a potential of a power source line, which is hardly influenced by noise such as power source ripple.
2. Description of the Related Art
A semiconductor amplifier circuit of audio equipment or a semiconductor amplifier circuit utilizing an operational amplifier has been driven by a single power source, that is, a positive or negative power source or driven by two power sources, that is, both a positive power source and a negative power source. In the single power source case, it is usual to connect a semiconductor substrate of the semiconductor amplifier circuit to a ground potential or a potential of a power source line as a reference potential. In the two-power source case, the amplifier circuit is designed by selecting a potential of a positive side power source line or a potential of a negative side of the power source line, which is the lowest, as a potential reference.
As shown in FIG.
4
(
a
), a transistor constituting a semiconductor amplifier circuit of this type, that is, a driving transistor
20
is formed by providing, for example, a P
+
isolation in a P type substrate
21
. This amplifier circuit is constituted as a transistor circuit
22
equivalent thereto as shown in FIG.
4
(
b
). An input signal is input to an input terminal IN and an output signal is output at an output terminal OUT. In such circuit, parasitic diodes Dk are formed simultaneously in a reverse direction between an emitter and a base or between the emitter and a collector through the P type substrate
21
and, further, a parasitic capacitance Ck is formed.
The parasitic elements such as diodes or parasitic capacitor are necessarily formed due to the structure of the IC and, when a voltage lower than the reference potential set in the input terminal IN is applied thereto, the parasitic diodes Dk are turned ON, so that there is a problem that currents may flow from the substrate side to the respective transistor forming layers. In order to solve such problem, it is usual to not apply a voltage lower than the substrate potential (reference potential) to the input terminal IN. in order to realize the latter, the potential reference mentioned above must be employed.
FIG. 5
shows a circuit diagram of a semiconductor amplifier circuit operable with a positive and negative power sources.
In
FIG. 5
, an amplifier circuit
8
formed in a semiconductor integrated circuit is constructed with an amplifier circuit
1
and constant current sources
2
and
3
connected to a negative power source line −Vcc. The amplifier circuit
1
has an input terminal
8
a
and an output terminal
8
b
. A differential amplifier circuit
4
is provided as an input stage and an output amplifier
5
is provided as an output stage. An input signal Vin is supplied from a preceding stage to the input terminal
8
a.
The differential amplifier circuit
4
includes npn type differential transistors Q
1
and Q
2
having emitters commonly connected to the constant current source
2
through which the emitters are connected to the negative side power source line −Vcc. Further, pnp transistors Q
3
and Q
4
which constitute a current mirror circuit are connected to collectors of the respective npn type differential transistors Q
1
and Q
2
as loads thereof. The collectors of the transistors Q
3
and Q
4
are connected to the positive side power source +Vcc.
The constant current source
2
is constituted with npn type transistors Q
5
and Q
6
which constitute a current mirror circuit. The diode-connected, input side transistor Q
6
is supplied with a constant current from a constant current source
7
and the output transistor Q
5
of the current mirror circuit sinks a constant current from the common emitters of the differential transistors Q
1
and Q
2
.
A base of the differential transistor Q
1
is connected through a resistor Rs to the input terminal
8
a
and a base of the differential transistor Q
2
is grounded.
The output amplifier
5
is constituted with a pnp type transistor Q
7
having an emitter connected to the power source line +Vcc, a collector connected to the output terminal
8
b
and through the constant current source
3
to the negative power source line −Vcc and a base connected to the collector of the differential transistor Q
1
.
An output voltage at the output terminal
8
b
is applied through a feedback resistor Rf to the base of the differential transistor Q
1
.
Since the constant current source
3
is constructed similarly to the constant current source
2
, details thereof is omitted.
In the circuit shown in
FIG. 5
, a reference potential at the substrate is usually set to the negative side power source potential −Vcc. In such circuit, the ground potential which is an intermediate potential between the positive and negative power source potentials is not used as the reference potential for the reason mentioned previously. Therefore, an output signal Vo obtained at the output terminal
8
b
tends to be influenced by a potential variation of the substrate.
Particularly, in an integrated circuit, a number of circuits are operated by a power source. Therefore, ripple of its power source voltage is unavoidable. Since the substrate side potential, that is, the negative side power source potential −Vcc and the positive side power source potential +Vcc are relative, the substrate side potential is varied by the ripple voltage when looked from the positive side power source potential +Vcc. When the potential of the substrate is varied with the ripple, signals tend to enter through the parasitic capacitance Ck into respective circuits of the integrated circuit and appear as noise signals. Further, in the worst case, the parasitic diodes Dk are turned ON, causing the integrated circuit to be operated erroneously.
The problem of such power source ripple becomes severe when a plurality of amplifier circuits driven by both the positive and negative power sources are integrated as a single semiconductor, because the power source ripple is increased due to increased difference in potential between the positive power source and the negative power source and the negative side power obtained by driving the internal circuit generating the negative power source voltage with a power from the positive power source circuit.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor amplifier circuit which is hardly influenced by noise such as power source ripple when it is driven by one or both of a positive power source and a negative power source.
In order to achieve the above object, a semiconductor amplifier circuit according to the present invention comprises a semiconductor substrate of one of a P type and an N type, a well region of the same type as that of the substrate, formed in the substrate, a well region defining region of the other type, including a side wall portion and a bottom portion defining the well region, a first transistor formed in the well region and a second transistor formed on a surface of other portion of the substrate than a portion on which the well region is formed. During the first and second transistors are in operation, a potential of the substrate is set to a reference potential, a potential of the well region defining region is set equal to the potential of the substrate or set to a value with which a junction between the well region defining region and the substrate is reverse-biased and at least one of electrodes of the first transistor is set to a potential with which a junction between the well region defining region and the well region is reverse-biased.
In such amplifier circuit, the conductivity type of the well region defining region is
Adachi Kengo
Hoshino Taichi
Oyama Eitaro
Mattingly Stanger & Malur, P.C.
Nu Ton My-Trang
Rohm & Co., Ltd.
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