Amplifier and mixer with improved linearity

An amplifier circuit comprising:

• first and second main active devices each having a first, a second, and a third terminal, wherein quantity and direction of current flowing from the second terminal to the third terminal varies depending on voltage driven to the first terminal, and said first and second main active devices are serially coupled such that the third terminal of said first main active device is coupled to the second terminal of said second main active device;
• an auxiliary active device having a first, a second, and a third terminal, wherein quantity and direction of current flowing from the second terminal to the third terminal varies depending on voltage driven to the first terminal, and the third terminals of said first main active device and said auxiliary active device are connected;
• and
• a biasing unit connected to the first terminals of said first and second main active devices, the first terminal of said auxiliary active devices, the third terminal of said second main active device, voltage source, an input terminal, and an output terminal, by which said first and second main active devices operate primarily in a saturation region and said auxiliary active device operates primarily in a sub-threshold region.

A mixer circuit comprising:

• a main active device having a first, a second, and a third terminal, wherein quantity and direction of current flowing from the second terminal to the third terminal varies depending on voltage driven to the first terminal,
• an active device pair comprising two active devices, each having a first, a second, and a third terminal, wherein quantity and direction of current flowing from the second terminal to the third terminal varies depending on voltage driven to the first terminal, and
• wherein said main active device and said active device pair are serially coupled such that the third terminal of said main active device is coupled to the second terminals of said active devices in said active device pair;
• an auxiliary active device having a first, a second, and a third terminal, wherein quantity and direction of current flowing from the second terminal to the third terminal varies depending on voltage driven to the first terminal, and the third terminals of said first main active device and said auxiliary active device are connected;
• and
• a biasing unit connected to the first terminals of said main active device and the active devices in said active device pair, the first terminal of said auxiliary active device, voltage source, and input terminal, and an output terminal, by which said main active device operates primarily in a saturation region and said auxiliary active device operates primarily in a sub-threshold region.