Patent ID: 7463862

Claim:
An image-rejection quadrature mixer comprising: an input terminal; a first pair of output terminals including an I+ terminal and an I− terminal; a second pair of output terminals including a Q+ terminal and a Q− terminal; a mixer coupled between the input terminal and the first and second pairs of output terminals, the mixer to form from a radio frequency signal coupled to the input terminal a diffential in-phase signal at the first pair of output terminals and a differential quadrature signal at the second pair of output terminals; and an active load coupled between the first and second pairs of output terminals, the active load to present a frequency-dependent impedance to the mixer to control an image-rejection response of the mixer, the mixer and the active load being integrated on a common silicon substrate, the active load comprising: first and second current mirrors; a first differential pair of transistors including a first transistor and a second transistor, the first transistor having a first gate coupled to the I+ terminal, a first source coupled to the Q− terminal, and a first drain coupled to the first current mirror, the second transistor having a second gate coupled to the I+ terminal, a second source coupled to the Q− terminal, and a second drain coupled to the first current mirror; and a second differential pair of transistors including a third transistor and a fourth transistor, the third transistor having a third gate coupled to the Q+ terminal, a third source coupled to the I+ terminal, and a third drain coupled to the second current mirror, the fourth transistor having a fourth gate coupled to the Q− terminal, a fourth source coupled to the I− terminal, and a fourth drain coupled to the second current mirror; wherein the first and second differential pairs have effective transconductances based on tail currents of the first and second current mirrors, and a center frequency of the image-rejection response being based on the effective transconductances.