A 2.4 GHz four port mixer for direct conversion used in telemetering

In telemetering systems, there is a strong desire for low power, low cost and monolithic integrated transceiver. Direct conversion has been found to be suitable for these needs. However, challenges arise in the design of mixers for direct conversion due to the poor RF-LO isolation. Without a careful design, the undesirable DC offset may seriously handicap the direct conversion technique. This paper presents a 0.35 μm 2.4 GHz CMOS four port mixer for up and down conversion. The mixer designed is based on Gilbert cell but employs current injection for up conversion input with improved linearity. With the use of an additional mixer port in the proposed transceiver architecture, it provides a capability to combine the up and down converter in the same circuit with better performance. The mixer is powered at 2V and drains 5 mA. The IIP3 and single side band noise figure is 5 dBm and 18dB@2MHz. The conversion gain of the mixer is 9 dB for down conversion and the conversion loss is 18 dB for up conversion