US 5,627,490 AGranted

Amplifier circuit

AssigneeMatsushita Electric Industrial Co., Ltd.

InventorsKoji Sushihara, Takashi Yamamoto, Ikuo Imanishi, Tsuyoshi Nakamura, Michinori Kishimoto, Kenichi Ishida

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Abstract

An amplifier circuit for amplifying a change in a resistance value of a magnetic resistance element is formed by connecting a first and a second current mirror circuits having the same structure in cascode, so that a voltage change is amplified without using a capacitive coupling. Hence, a high-pass filter is not created as a parasitic circuit, whereby a gain is maintained high in the low frequency region and a low frequency characteristic is excellent. Further, since control electrodes of transistors which form each current mirror circuit are grounded through the capacitance, a noise is reduced without using a conventional feedback circuit. This eliminates an influence of the feedback circuit over a high frequency characteristic, and therefore, a high frequency characteristic becomes excellent.

Claims19

Dependent claims

An amplifier circuit, comprising:

a first current mirror circuit and a second current mirror circuit;
a first resistor;
a resistor member whose resistance value changes due to an external factor;
a current supply circuit;
and
a second resistor,
wherein said first and said second current mirror circuits have the same structure, said first and said second current mirror circuits each comprise:
a first input terminal and a first output terminal;
a first transistor which is coupled between the first input terminal and the first output terminal, said first transistor having a control electrode connected to said first input terminal;
a second input terminal and a second output terminal;
and a second transistor which is coupled between the second input terminal and the second output terminal, said second transistor having a control electrode connected to said first input terminal, said control electrodes of said first and said second transistors are connected to a set potential through a capacitance,
the first and the second input terminals of said first current mirror circuit are connected to the first and the second output terminals of said second current mirror circuit, respectively,
said first resistor is coupled between the first output terminal of said first current mirror circuit and a set constant potential,
said resistor member is disposed between the second output terminal of said first current mirror circuit and said set constant potential,
said current supply circuit is connected to the first input terminal of said second current mirror circuit,
said second resistor is coupled between a power source and the second input terminal of said second current mirror circuit, and
a change in the resistance value of said resistor member is outputted as a change in a voltage which is developed across said second resistor.

14 more elements

An amplifier circuit, comprising:

a first current mirror circuit and a second current mirror circuit;
a first resistor;
a current supply circuit;
a second resistor;
a third resistor and
an alternate current generation circuit,
wherein said first and said second current mirror circuits have the same structure, said first and said second current mirror circuits each comprises:
a first input terminal and a first output terminal;
a first transistor which is coupled between the first input terminal and the first output terminal, said first transistor having a control electrode connected to said first input terminal;
a second input terminal and a second output terminal;
and a second transistor which is coupled between the second input terminal and the second output terminal, said second transistor having a control electrode connected to said first input terminal, said control electrodes of said first and said second transistors are connected to a set potential through a capacitance,
the first and the second input terminals of said first current mirror circuit are connected to the first and the second output terminals of said second current mirror circuit, respectively,
said first resistor is coupled between the first output terminal of said first current mirror circuit and a set constant potential,
said third resistor is coupled between the second output terminal of said first current mirror circuit and said set constant potential, to receive an alternate current signal from said alternate current generation circuit,
said current supply circuit is connected to the first input terminal of said second current mirror circuit,
said second resistor is coupled between a power source and the second input terminal of said second current mirror circuit, and
a change in the value of a current which is supplied to said third resistor from said second current mirror circuit is outputted as a change in a voltage which is developed across said second resistor.

14 more elements

An amplifier circuit, comprising:

a plurality of input blocks each consisting of a first current mirror circuit, a first resistor, a resistor member whose resistance value changes due to an external factor;
a selector circuit for selecting one of said plurality of input blocks;
a second current mirror circuit;
a current supply circuit;
and
a second resistor,
wherein said first and said second current mirror circuits have the same structure, said first and said second current mirror circuits each comprises:
a first input terminal and a first output terminal;
a first transistor which is coupled between the first input terminal and the first output terminal, said first transistor having a control electrode connected to said first input terminal;
a second input terminal and a second output terminal;
and a second transistor which is coupled between the second input terminal and the second output terminal, said second transistor having a control electrode connected to said first input terminal, said control electrodes of said first and said second transistors are connected to a set potential through a capacitance,
in each one of said input blocks:
the first and the second input terminals of said first current mirror circuit are connected to the first and the second input terminals of said second current mirror circuit, respectively;
said first resistor is coupled between the first output terminal of said first current mirror circuit and a set constant potential;
said resistor member is coupled between the second output terminal of said first current mirror circuit and said set constant potential,
said current supply circuit is connected to the first input terminal of said second current mirror circuit,
said second resistor is coupled between a power source and the second input terminal of said second current mirror circuit, and
a change in the resistance value of said resistor member which belongs to one of the input blocks which is selected by said selector circuit is outputted as a change in a voltage which is developed across said second resistor.

15 more elements

Dependencies are inferred from the claim text.