Gaussian Low Pass Filter
By Brett Eller and Ryan Dejmal
This part of the project is devoted to getting digital input to the Voltage Controlled Oscillator (VCO) in a form it can handle. First, the digital data is converted to a differential signal to reduce the effects of noise. Then, the signal is passed through a Gaussian Low Pass Filter (LPF) to define the transmitted FSK signal's spectrum occupancy. The LPF is a 500kHz 3rd order ladder filter which is finely tunable. The filter utilizes master-slave tuning to accurately control the filter frequency despite temperature and process variations. Once the filtering is complete, the signal is then sent to the VCO. In order to find more information about either design, follow the links below.
Digital to Differential Converter