TILowPowerRF.pptVIP

TI Low Power RF Designers Guide to LPRF Considerations when starting an RF design: How many members/nodes will participate the wireless network? What is the required range between the devices? Is there a special need for low power consumption? Are there common standards that have to be met? How far can TX and RX be apart from each other? Friis’ transmission equation for free space propagation: or Pt is the transmitted power, Pr is the received power Gt is the transmitter, Gr is the receiver antenna gain d is the distance between transmitter and receiver, or the range Lambda is the wavelength Compared to the estimated range we should get in theory here are some ”real life” rules and experiences on RF range: 120 dB link budget at 433 MHz gives approximately 2000 meters (TI rule of thumb) Based on the emperical results above and Friis’ equation estimates on real range can be made Rule of Thumb: 6 dB improvement ~ twice the distance Double the frequency ~ half the range (433 MHz longer range than 868 MHz) Antenna (gain, sensitivity to body effects etc.) Sensitivity: Lowest input power with acceptable link quality (typically 1% PER) Channel Selectivity: How well a chip works in an environment with interference Output power Environment (Line of sight, obstructions, reflections, multi-path fading) Low Power characteristics and features of TI’s RF devices: Low sleep current Minimum MCU activity RX/TX turn around time Adaptive output power using RSSI Fast crystal start-up time Fast PLL calibration (and settling) Carrier sense recognition Low RX peak current Minimum duty cycle Wake on radio (new devices) Use the lowest possible duty cycle Send data only when needed, do not send more data than necessary Use the highest data rate you can (trade-off vs. range) Watch out for protocol-related overhead Use the lowest possible voltage RF chips have reduced current draw at lower voltages Low voltage degrades RF performance Above not a proble