Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
1999-06-08
2001-02-20
Shingleton, Michael B (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
C330S310000, C330S261000, C330S259000, C330S257000
Reexamination Certificate
active
06191654
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a differential amplifier circuit and more particularly to a differential amplifier circuit which is able to amplify and output a difference voltage between a pair of input voltages.
2. Description of the Related Art
FIG. 4
shows a well-known conventional differential amplifier circuit. In this circuit, a pair of input terminals IN− and IN+ are connected with two ends of a signal source
10
. An output voltage Vin of the signal source
10
is superimposed on an output voltage V1 of a DC voltage power supply
11
which is connected with the input terminal IN+, and is applied across the input terminals IN− and IN+.
The input terminals IN− and IN+, via respective resistances R1, are connected with inverting and non-inverting input terminals of an operational amplifier
12
. The inverting input terminal of the operational amplifier
12
, via a resistance R2, is connected with an output terminal of the operational amplifier
12
and an output terminal
14
. The non-inverting input terminal of the operational amplifier
12
is connected with a DC voltage power supply
13
of a voltage V2 via a resistance R3. In addition, the operational amplifier
12
is supplied with a power source and a ground.
The differential amplifier circuit amplifies R2/R1 times the signal voltage Vin which is superimposed on the DC voltage V1, and thereafter superimposes the amplified voltage on the DC voltage V2 so as to output an amplified-and-superimposed voltage Vout.
In the conventional circuit shown in
FIG. 4
, the DC voltage V1, being superimposed with the signal voltage Vin, must be small enough to meet a condition “0<VA<Vcc” with respect to the power supply Vcc and ground (0V) of the operational amplifier
12
. In the above, “VA” denotes a voltage of the non-inverting input terminal of the operational amplifier
12
.
For example, in a case of using the above-mentioned differential amplifier circuit as a current sense amplifier circuit for detecting a current charging or discharging a secondary accumulator, since the secondary accumulator outputs a voltage having a large voltage variation, the power supply Vcc of the differential amplifier circuit supplies a stable voltage by using a regulator to stabilize the output voltage of the secondary accumulator. In general, an output voltage of the regulator is lower than that of the secondary accumulator because of a relationship “VA=R2(V1−V2)/(R1+R2)”.
However, in a current sense amplifier in which a differential voltage between two ends of a small resistance inserted between a secondary accumulator and a load is amplified by a differential amplifier circuit, respective voltages applied to the two ends of the small resistance are about as high as an output voltage of the secondary accumulator and higher than an output voltage of the regulator. For this reason, the current sense amplifier does not meet the condition “0<VA<Vcc” of the differential amplifier circuit in FIG.
4
and therefore cannot be applied in the above-mentioned current sense amplifier.
Furthermore, in the circuit of
FIG. 4
, if V1 is not equal to V2, an electric current I (I=(V1−V2)/(R1+R2)) always flows through the respective resistances R1 of the input terminals IN− and IN+, and, as a result, consumed power will be increased.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide a differential amplifier circuit in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a differential amplifier circuit capable of amplifying a differential voltage between a pair of input terminals even if respective voltages of the input terminals are higher than a source voltage.
According to one aspect of the present invention, there is provided a differential amplifier circuit for amplifying and outputting a differential voltage between a pair of input terminals, which differential amplifier circuit comprises a voltage-to-current converting circuit in which each of the input terminals is connected with one end of each of resistances, a potential on the other end of each of the resistances is kept constant by a feedback circuit, and an electric current corresponding to the differential voltage flows into a first differential circuit; a current amplifying circuit in which the electric current corresponding to the differential voltage and flowing into the first differential circuit is amplified and then flows into a second differential circuit; and a current-to-voltage converting circuit in which an electric current outputted from the current amplifying circuit is converted to a voltage and the voltage is outputted. The input terminals supply power to the voltage-to-current converting circuit consisting of transistors.
Thus, even though input voltages of the input terminals are higher than the source voltage, a differential voltage between the input terminals can be converted to an electric current so that the differential voltage can be amplified and outputted.
REFERENCES:
patent: 5966046 (1999-10-01), Bezzam et al.
patent: 6023196 (2000-02-01), Ashby et al.
Ikeuchi Akira
Makime Kyozo
Andrus Sceales Starke & Sawall LLP
Mitsumi Electric Co. Ltd.
Shingleton Michael B
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