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DESCRIPTION JPH05167358

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DESCRIPTION JPH05167358
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
amplifier circuit for two-wire ECM, and more particularly to an amplifier circuit using an
operational amplifier.
[0002]
2. Description of the Related Art An amplifier circuit of this type using a conventional single
power supply is shown in FIG. A bias voltage applied to the positive phase input terminal 10 of
the operational amplifier 2 is generated by a bias circuit 8 composed of voltage dividing resistors
4 and 5 and an AC bias capacitor 6. Further, since the 2-wire type ECM 3 in which the output is
inputted to the negative phase input terminal 14 of the operational amplifier 2 has the same
signal as the power supply, the power supply circuit 9 including the resistors 11 and 12 and the
capacitor 13 supplies the power to the ECM 3 Supply. The resistor 12 is a load resistor, and the
capacitor 13 functions to reduce noise contained in the power supply and not to degrade the S /
N ratio of the ECM 3. Further, the capacitor 20 sets a DC cut capacitor, and the resistors 21 and
22 set the gain of the operational amplifier 2. 1 is an output terminal.
[0003]
In such a conventional amplification circuit, a bias circuit 8 applied to the positive phase input
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terminal of the operational amplifier 2 and a power supply circuit 9 for supplying power to the
ECM 3 are required, Each has an independent circuit configuration. For this reason, in portable
devices expected to be small and light, reduction of the number of parts is promoted, but in the
above-described conventional configuration, the number of parts of the power supply circuits 8
and 9 is large, which is large for miniaturization of portable devices. It is a constraint. An object
of the present invention is to provide an ECM amplification circuit which can reduce the number
of parts by reducing the size of a power supply system circuit.
[0004]
SUMMARY OF THE INVENTION The ECM amplification circuit of the present invention is a
power supply system using a part of a bias circuit for applying a bias voltage to the positive
phase input terminal of an operational amplifier and a resistor connected to the bias circuit. The
circuit is configured to supply power to the ECM from the power supply circuit. For example, the
bias circuit comprises a pair of voltage dividing resistors connected in series between the power
supply and the ground, and a capacitor connected between the connection point of these
resistors and the ground, and the power supply circuit is on the power supply side , A capacitor,
and a resistor connected between the connection point and the ECM.
[0005]
The power supply circuit is supplied with power by the resistance of the bias circuit and the
newly connected resistance, whereby some parts of the power supply circuit are shared with the
parts of the bias circuit.
[0006]
Next, the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram of one embodiment of the present invention, and shows an
amplification circuit for a two-wire ECM operated by a single power supply. A bias voltage to be
applied to the positive phase input terminal 10 of the operational amplifier 2 is generated by a
bias circuit 8 composed of voltage dividing resistors 4 and 5 and a capacitor 6 for AC bias. The
bias voltage V1 input to the positive phase input terminal 10 of the operational amplifier 2 is
usually selected so that the operational amplifier can obtain the maximum output amplitude. The
resistance value is set.
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2
[0007]
Then, in order to supply power to the ECM 3 which inputs the output to the negative phase input
terminal 14 of the operational amplifier 2, the output terminal of the bias circuit 8, that is, the
positive phase input terminal 10 of the operational amplifier 2 and ECM 3 are connected by a
resistor 7 The resistor 7, the resistor 4 and the capacitor 6 constitute a power supply circuit 9. In
this case, the resistor 7 is a load resistor of the ECM 3, and the capacitor 6 is used to reduce the
noise contained in the power supply to the ECM 3 and not to degrade the S / N ratio of the ECM
3. The capacitor 20 sets a DC cut capacitor, and the resistors 21 and 22 set the gain of the
operational amplifier 2. 1 is an output terminal.
[0008]
According to this configuration, the power supply circuit 9 for supplying power to the ECM 3 can
be configured by using the resistor 4 and the capacitor 6 of the bias circuit 8 and attaching the
resistor 7 thereto. As a result, a part of the bias circuit 8 can be used also as a part of the power
supply circuit 9, the number of parts can be reduced accordingly, and downsizing and weight
reduction of the portable device can be realized.
[0009]
As described above, according to the present invention, the resistance is connected between the
connection point of the voltage dividing resistors of the bias circuit and the ECM, and power is
supplied to the ECM through these resistances. A part of the bias circuit can also be used as a
component of the power supply circuit for the ECM, reducing the number of parts, reducing the
scale of the amplifier circuit, and reducing the size and weight of the portable device. Have the
effect of
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