Amplifier and device having amplifier, and mutual conductance control method
An amplifier is provided with an amplifier circuit including a plurality of first transistors having gates thereof coupled in common, a bias circuit including a plurality of second transistors that are coupled and outputs a bias voltage to the gates of the plurality of first transistors, and a selection circuit simultaneously controlling a number of first transistors to be coupled to the amplifier circuit and a number of second transistors to be coupled to the bias circuit based on the bias voltage.
1. An amplifier comprising:
an amplifier circuit including a plurality of first transistors having gates thereof coupled in common, wherein a number of said first transistors that are actively coupled to said amplifier circuit is variable;
a bias circuit, including a plurality of second transistors that are coupled, configured to output a bias voltage to the gates of the plurality of first transistors, wherein a number of said second transistors that are actively coupled to said bias circuit is variable; and
a selection circuit configured to simultaneously control a number of first transistors to be actively coupled to the amplifier circuit and a number of second transistors to be actively coupled to the bias circuit, based on the bias voltage.
2. The amplifier as claimed in claim 1 , wherein the bias circuit includes a number of second transistors identical to a number of first transistors of the amplifier circuit.
3. The amplifier as claimed in claim 1 , wherein the selection circuit carries out a control to increase the number of first and second transistors that are to be actively coupled, if a transconductance of the first transistors is lower than a predetermined value and the bias voltage is higher than a predetermined voltage.
4. The amplifier as claimed in claim 1 , wherein the selection circuit carries out a control to reduce the number of first and second transistors that are to be actively coupled if a transconductance of the first transistors is higher than a predetermined value and the bias voltage is less than or equal to a first threshold voltage so as to reduce the transconductance, and to increase the number of first and second transistors that are to be actively coupled if the transconductance is lower than or equal to the predetermined value and the bias voltage is higher than or equal to a second threshold voltage that is higher than the first threshold voltage.
5. The amplifier as claimed in claim 1 , wherein the selection circuit carries out a control so that a transconductance of the first transistors that are to be actively coupled is higher than a predetermined value in a using region of the first transistors that are to be actively coupled.
6. The amplifier as claimed in claim 1 , wherein the amplifier circuit and the bias circuit control connections of the first and second transistors using a plurality of switches, based on a signal from the selection circuit.
7. A transconductance control method comprising:
a control step controlling an operating point of a plurality of transistors of an amplifier circuit by outputting a bias voltage to the amplifier circuit so that a transconductance of the plurality of transistors becomes constant; and
a selection step outputting to the amplifier circuit a signal that controls a number of transistors to be actively used in the amplifier circuit, of the plurality of transistors of the amplifier circuit, based on the bias voltage.
8. The transconductance control method as claimed in claim 7 , wherein the selection step carries out a control to reduce the number of transistors to be actively used if the transconductance of the transistors is higher than a predetermined value and the bias voltage is less than or equal to a first threshold voltage so as to reduce the transconductance, and to increase the number of transistors to be actively used if the transconductance is lower than or equal to the predetermined value and the bias voltage is higher than or equal to a second threshold voltage that is higher than the first threshold voltage.
9. The transconductance control method as claimed in claim 7 , wherein the selection step carries out a control so that the transconductance of the transistors that are to be actively used is higher than a predetermined value in a using region of the transistors that are to be actively used.
10. A transconductance control method comprising:
a control step controlling an operating point of a plurality of transistors of a predetermined circuit by outputting a bias voltage to the predetermined circuit so that a transconductance of the plurality of transistors becomes constant; and
a selection step outputting to the predetermined circuit a signal that controls a number of transistors to be actively used in the predetermined circuit, of the plurality of transistors of the predetermined circuit, based on the bias voltage,
wherein the predetermined circuit includes at least one circuit selected from a group consisting of an amplifier circuit, a limiter circuit and a mixer circuit.