Switched Transconductor Mixer Compatible with Future CMOS

Mixers are commonly used in communication systems for frequency translation, and usually exploit switching in some form to implement multiplication by a square wave. However, at the low supply voltages required for new CMOS technologies, switches are non- or poorly conducting in the "middle voltage range" between the supply voltages. To solve this problem, gates are often driven outside the supply voltage range, but this results in gate-oxide reliability problems, especially in future technologies with very thin oxides. We propose a new CMOS mixer topology that can operate at low supply voltages, without driving gates outside the supply range. It exploits only switches connected to the supplies, just as in digital CMOS inverters. Mixing is achieved exploiting two cross-coupled transconductors, which are alternatingly activated and de-activated by the switches. A down conversion mixer prototype with 12 dB conversion gain was designed and realized in standard 0.18μm CMOS. It achieves satisfactory mixer performance up to 4GHz, at a supply voltage of 1 Volt. Moreover, the mixer topology features a fundamental high frequency noise figure benefit.