Parabolic Crystal Drift Compensation Mechanics in Battery Powered Sub-GHz Endpoints
Digital frequency compensation corrects parabolic crystal drift in sub-GHz endpoints by recalculating synthesizer division registers using onboard thermal readings.
Receiver Passband Attenuation
Meaning
Signal loss within the desired reception frequency range reduces the overall sensitivity of a radio system. The presence of receiver passband attenuation means that weak signals may fall below the noise floor before they are processed. Designers aim to minimize this value to maximize the communication range of the device.
Filter Performance
Selectivity requirements often conflict with the goal of low insertion loss. While receiver passband attenuation is undesirable, the filters that cause it are necessary to block out of band interference from other transmitters. Choosing a filter with a sharp slope often results in more loss at the center frequency.
Sensitivity Degradation
Increasing the loss in the front end directly raises the noise figure of the entire chain. Each decibel of receiver passband attenuation subtracted from the input signal is a decibel lost in the total link budget. This effect is particularly damaging in long range systems where every fraction of a milliwatt is needed to maintain a stable connection.
Low noise amplifiers can compensate for some loss, but they also introduce their own noise and consume additional power. The placement of the first filter before the amplifier is a common trade off between interference protection and sensitivity.
Component Loss
Physical properties of the substrate and the conductor define the minimum achievable loss. Excessive receiver passband attenuation can occur if the copper traces are too thin or if the dielectric material has a high dissipation factor. High quality laminates and gold plating are often used to reduce these resistive and dielectric losses in high frequency designs.