Transconductance amplifier
First Claim
1. A transconductance amplifier which supplies an output current proportional to an input voltage, characterized by comprising:
- a differential pair which is formed of first and second MOS transistors having a common source, and which operates in a triode region;
a third MOS transistor of which a source terminal is connected to a drain terminal of the first MOS transistor, and which operates in a saturation region;
a fourth MOS transistor of which a source terminal is connected to a drain terminal of the second MOS transistor, and which operates in the saturation region;
a first amplifier of which a negative input terminal is connected to the source terminal of the third MOS transistor and of which an output terminal is connected to a gate terminal of the third MOS transistor;
a second amplifier of which negative input terminal is connected to the source terminal of the fourth MOS transistor and of which output terminal is connected to a gate terminal of the fourth MOS transistor;
a voltage generator circuit which generates a tuning voltage inputted to positive input terminal voltages of the first and second amplifiers, and a common voltage of first and second voltages inputted to the differential pair so that a difference between the tuning voltage and the common voltage is equal to a constant; and
a differential-pair input voltage generator circuit which is supplied with a common voltage, and which generates the first voltage outputted to a gate terminal of the first MOS transistor, and the second voltage outputted to a gate terminal of the second MOS transistor, characterized in thatthe second voltage is equal to 2×
(the common voltage)−
(the first voltage),the input voltage is equal to a difference between the first voltage and the second voltage, andthe output current is equal to a difference between a first current Ip flowing through the drains and sources of the first and third MOS transistors and a second current In flowing through the drains and sources of the second and fourth MOS transistors.
1 Assignment
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Accused Products
Abstract
Provided is a transconductance amplifier capable of suppressing variation in the range of a linear relationship between an input voltage and an output current depending on the magnitude of a tuning voltage Vctrl, thereby adjusting transconductance over a wider range of operating input voltages. The transconductance amplifier is configured by a differential pair formed of MOS transistors (111, 112) having a common source, MOS transistors (113, 114), amplifiers (106, 107), a voltage generator circuit (100), and a differential-pair input voltage generator circuit (120). An input differential common voltage Vcm of all differential signals inputted to the differential pair is adjusted so that a difference between Vcm and Vctrl is equal to a constant, in accordance with a change in the tuning voltage Vctrl that controls the transconductance. This enables keeping constant the range in which the transconductance amplifier can achieve good linearity.
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Citations
8 Claims
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1. A transconductance amplifier which supplies an output current proportional to an input voltage, characterized by comprising:
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a differential pair which is formed of first and second MOS transistors having a common source, and which operates in a triode region; a third MOS transistor of which a source terminal is connected to a drain terminal of the first MOS transistor, and which operates in a saturation region; a fourth MOS transistor of which a source terminal is connected to a drain terminal of the second MOS transistor, and which operates in the saturation region; a first amplifier of which a negative input terminal is connected to the source terminal of the third MOS transistor and of which an output terminal is connected to a gate terminal of the third MOS transistor; a second amplifier of which negative input terminal is connected to the source terminal of the fourth MOS transistor and of which output terminal is connected to a gate terminal of the fourth MOS transistor; a voltage generator circuit which generates a tuning voltage inputted to positive input terminal voltages of the first and second amplifiers, and a common voltage of first and second voltages inputted to the differential pair so that a difference between the tuning voltage and the common voltage is equal to a constant; and a differential-pair input voltage generator circuit which is supplied with a common voltage, and which generates the first voltage outputted to a gate terminal of the first MOS transistor, and the second voltage outputted to a gate terminal of the second MOS transistor, characterized in that the second voltage is equal to 2×
(the common voltage)−
(the first voltage),the input voltage is equal to a difference between the first voltage and the second voltage, and the output current is equal to a difference between a first current Ip flowing through the drains and sources of the first and third MOS transistors and a second current In flowing through the drains and sources of the second and fourth MOS transistors. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification