DC bias circuit and the radio frequency receiver circuit using the same

1. A DC bias circuit for DC biasing a mixer circuit and a common gate amplifier circuit, the DC bias circuit comprising:

a first biasing circuit, comprising a first biasing transistor and a first biasing resistor, wherein the first biasing transistor and the first biasing resistor provide a first DC bias voltage to an output transistor of the mixer circuit so that the output transistor operates in a saturation region,

wherein the first biasing transistor and the output transistor are the same type of transistor and have equal channel lengths; and

a second biasing circuit, comprising a second biasing transistor and a second biasing resistor, wherein the second biasing transistor and the second biasing resistor provide a second DC bias voltage to an input transistor of the common gate amplifier circuit so that the input transistor operates in the saturation region,

wherein the second biasing transistor and the input transistor are the same type of transistor and have equal channel lengths, and

wherein when the input transistor and the output transistor all operate in the saturation region, a plurality of alternating current signals output from the mixer circuit is unrelated to a threshold voltage of the output transistor, and the alternating current signals is unrelated to a threshold voltage of the input transistor.

2. The DC bias circuit of claim 1 , wherein the common gate amplifier circuit is a differential common gate amplifier, and the differential common gate amplifier further comprises another input transistor,

wherein the second biasing circuit provides the second DC bias voltage to the other input transistor through the second biasing transistor and the second biasing resistor so that the other input transistor operates in the saturation region, and

wherein the second biasing transistor and the other input transistor are the same type of transistor and have equal channel lengths.

3. The DC bias circuit of claim 1 , wherein the mixer circuit is a passive complementary metal-oxide-semiconductor (CMOS) mixer circuit, and the passive CMOS mixer circuit further comprises another output transistor,

wherein the first biasing circuit provides the first DC bias voltage to the other output transistor through the first biasing transistor and the first biasing resistor so that the other output transistor operates in the saturation region, and

wherein the first biasing transistor and the other output transistor are the same type of transistor and have equal channel lengths.

4. A DC bias circuit for DC biasing a mixer circuit and a common gate amplifier circuit, the DC bias circuit comprising:

a first biasing circuit, providing a first DC bias voltage to a gate of a first transistor of the mixer circuit so that the first transistor operates in a saturation region, wherein the first biasing circuit comprises:

a third transistor, wherein a gate and a drain of the third transistor are electrically connected to a first node, a source of the third transistor is electrically connected to ground, and the first and third transistor are the same type of transistor;

a first resistor, electrically connected between the gate of the first transistor and the first node; and

a first current source, used to output a first DC current to the third transistor; and

a second biasing circuit, providing a second DC bias voltage to a gate of a second transistor of the common gate amplifier circuit so that the second transistor operates in a saturation region, wherein the second biasing circuit comprises:

a fourth transistor, wherein a gate and a drain of the fourth transistor are electrically connected to a second node, a source of the fourth transistor is electrically connected to ground, and the second and fourth transistor are the same type of transistor;

a second resistor, electrically connected between the gate of the second transistor and the second node; and

a second current source, used to output a second DC current to the fourth transistor, wherein the mixer circuit receives a high-frequency input signal through a drain of the first transistor and outputs an alternating current signal through a source of the first transistor,

wherein the common gate amplifier circuit receives the alternating current signal through a source of the second transistor and outputs an alternating voltage signal through a drain of the second transistor,

wherein the source of the first transistor and the source of the second transistor are electrically connected to a third node, and a third current source is electrically connected between the third node and ground, and

wherein the first and third transistors have equal channel lengths, and the second and fourth transistors have equal channel lengths so that a plurality of alternating current signals output from the mixer circuit is unrelated to a threshold voltage of the output transistor.

5. A radio frequency receiver circuit, comprising:

a mixer circuit, comprising a first transistor, wherein the mixer circuit receives a plurality of radio frequency signals by a drain of the first transistor and outputs a plurality of alternating current signals by a source of the first transistor;

a common gate amplifier circuit, comprising a second transistor, wherein the common gate amplifier circuit receives the alternating current signals through a source of the second transistor and outputs a plurality of alternating voltage signals through a drain of the second transistor;

a first biasing circuit, used to provide a first DC bias voltage to a gate of the first transistor of the mixer circuit so that the first transistor operates in a saturation region, wherein the first biasing circuit comprises:

a third transistor, wherein a gate and a drain of the third transistor are electrically connected to a first node, a source of the third transistor is electrically connected to ground, and the first and third transistor are the same type of transistor;

a first resistor, electrically connected between the gate of the first transistor and the first node; and

a first current source, used to output a first DC current to the third transistor; and

a second biasing circuit, providing a second DC bias voltage to a gate of the second transistor of the common gate amplifier circuit so that the second transistor operates in a saturation region, wherein the second biasing circuit comprises:

a fourth transistor, wherein a gate and a drain of the fourth transistor are electrically connected to a second node, a source of the fourth transistor is electrically connected to ground, and the second and fourth transistor are the same type of transistor;

a second resistor, electrically connected between the gate of the second transistor and the second node; and

a second current source, used to output a second DC current to the fourth transistor, wherein the mixer circuit receives a high-frequency input signal through the drain of the first transistor and outputs an alternating current signal through the source of the first transistor,

wherein the source of the first transistor and the source of the second transistor are electrically connected to a third node, and a third current source is electrically connected between the third node and ground, and

wherein the first and third transistors have equal channel lengths, and the second and fourth transistors have equal channel lengths so that a plurality of alternating current signals output from the mixer circuit is unrelated to a threshold voltage of the output transistor.