The topic of my thesis project was designing the optical-to-electrical transducer, or receiver unit of an optical transmission network. The receiver unit to be designed has to be able to receive 900 MHz GSM signals, which are used worldwide to the date, and amplify them with keeping the noise figure as low as possible, compensating the attenuation during the optical transmission.
Designing the receiver unit includes matching the PIN diode used to optical-to-electrical conversion in a narrow band. It also includes designing and simulating a bandpass filter with 900 MHz center frequency, and the input and output matching network of the RF transistor used to the signal amplification. The design also includes biasing the transistor properly.
This was followed by the testing of the designed circuits, during which it was examined if the components fulfill the required specifications. This section included tuning the devices based on the measurements.
Finally, I made several measurements concerning the signal transmission on the full receiver unit. These included measuring the noise factor of the amplifier, and examining the transmission parameters of a 900 MHz signal, as well as the error magnitude vector of a QPSK-modulated signal.
The design and simulations were done with the Microwave Office program; the measurements were made with the devices in the OMT laboratory. The printed circuits were produced by the Department of Electronics and Technology.