Bias Supply Handles GaAsFET Power Amps

A negative regulated switched capacitor voltage inverter that generates a low-noise bias to control the output power of GaAs power amplifiers in cell phones, LM2687 typically produces ±1 mV output ripple with £1 ms startup time to prolong battery life and simplify power amplifier design. This device inverts a positive voltage in the range of 2.7V to 5.5V directly from a lithium-ion battery or fixed, lower noise power source. The voltage is then regulated by an adjustable low dropout linear regulator to provide up to 10 mA between -1.5V and -4.5V. The low ±1 mV output ripple is well below the threshold of concern for RF distortion. The short startup time of £1 ms saves battery life and lets the LM2687 be used in TDMA communications protocols such as PDC in Japan and GSM worldwide.