An RF transmitter provides both GSM and EDGE capability by implementing
collector voltage control over the power transistor(s) in a power
amplifier. During EDGE mode, linear base-biasing a power amplifier (PA)
allows collector control to provide either saturated mode PA operation
(during ramp up/ramp down) or linear mode PA operation (during data
burst). Collector control can therefore be used to provide the accurate
ramp up and ramp down profiles required for both GSM and EDGE burst
output signals, and can also be used to set the level of the constant
envelope data burst of a GSM burst output signal, while linear mode PA
operation can provide the non-constant envelope EDGE data burst. A
variable gain amplifier is used to adjust the input signal to the power
amplifier such that the desired transmission level is achieved.