Local oscillator generation circuit for direct conversion transmitter
In this paper a fully monolithic on-chip local oscillator signal generation circuit is presented for eliminating the negative effect of coupling between bond-wires, package pins and output and input lines of the power amplifier output to the local oscillator input for direct conversion transmitters. The proposed circuit generates the local oscillator signal at frequencies 1710-1785 GHz which is harmonically uncorrelated from two input signals at 464 MHz and 1792-2088 MHz. The required building blocks are a frequency divider, a mixer and an active band-pass filter. Fully monolithic high frequency band-pass filters have not been available until recently, and the designed circuit is in fact one of the first applications reported for MMIC active filters in cellular phones. The circuit is designed with a 0.5 mu m GaAs MESFET technology and the performance is verified with on-chip measurements.
local oscillator direct conversion transmitter mmic monolithic active filter