Mixer

While a typical mixer circuit uses a much more complicated topology, such as a six transistor gilbert cell, in this lab I design a single balanced transistor mixer because it is the most straightforward to build by hand. I learn about how to split RF and LO signals using a branch line coupler. I build a branch line coupler using only microstrip copper tape to send both the RF and LO signals to the transistor mixer with a 90 degree phase shift. I characterize the mixer by simulating and measuring the down conversion gain. The simulated design is built with extreme precision in order to minimize the effects of stray inductance and capacitance. From previous labs, I know that these effect can be devastating to the functionality of an RF circuit.