A fully differential 5V buffer for RF mixer output with current and linearity control

A design of a 5 volts buffer with current consumption and linearity control is presented. This buffer, with a low output impedance, is fully differential and designed for RF (radio frequency) mixer in low IF (intermediate frequency) architecture. The proposed buffer is directly connected to the output of the RF mixer to drive off-chip low impedance load as SAW (surface acoustic wave) or discrete differential filters. A good flexibility is obtained on the control of the linearity performance with the possibility to adjust the power consumption. Linearity and current consumption are independently adjustable and an optimum of the third order linearity performance is achieved for each current consumption value. A schematic of the differential bipolar 5 Volts buffer is proposed. Some linearity simulation results are presented and discussed in terms of output IM3 (Third order Intermodulation) level and current consumption. The results show a saving of half power in comparison with a buffer with no linearity control for the same output IM3 level.