12/4/2023 0 Comments Bipolar transistor rf mixerChoosing each component value is important if you care about the performance and meeting a specification.īut what about other amplifier designs? The common base amplifier for example looks a little weird depending on how it is drawn, and it’s purpose is not obvious when you learn it has a low input impedance and high output impedance: The tutorials on the internet will help you choose all the values to meet your requirements. So, in this circuit (which has a 12V supply) you can see the voltages at the important points as well as the currents in the various devices. In the end you will have a circuit where you have chosen all the voltages and currents to meet the design objective: Lastly you will also have a voltage swing to consider. You will have a gain and bandwidth requirement and a load impedance to drive. In the case of a common emitter amplifier you will have a signal source impedance which dictates what your amplifier input impedance should be to minimise loading of the signal source. ![]() For a linear amplifier, the standard common emitter amplifier is a typical example and there are plenty of very good tutorials to explain how to design one on the internet – simply search for biasing common emitter amplifiers and you will find many good examples.īiasing is about choosing the voltages at various key points in a circuit and the currents flowing through devices to meet the design objective. Also, if you are designing a high speed switch then biasing actually may come into the design to speed up the switching and minimise transition times. When used as a “switch” you simply want the transistor to be ON or OFF and don’t really care about having in-between states, although when you are switching high power or switching quickly the in-between states become important. Bipolar transistors used in linear applications need “biasing”, as do other transistors (JFET, MOSFET) when used for linear applications rather than as switches.
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