ISM Transmitter Has Constant Transmitter Power for Varying Supply Voltage
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In battery-powered RF transmitters such as garage door openers and remote keyless entry for cars, as the battery drains, the transmit power typically falls. This application note demonstrates that combining a high-efficiency step-up, or boost, voltage converter with an ISM transmitter will keep the transmitted power constant (under 0.5dB variation) over the battery voltage range. Performance data will show that the battery life for constant transmit power is up to 2 times that of a transmitter whose power drops as the battery voltage drops.