Power detection technique for automatic amplifier power control

A controlled-output power amplifier for providing power output control over a wide dynamic range, said controlled-output amplifier comprising:

• a power amplifier having an input for receiving an input signal and an output for providing a power output signal;
• power detector means for receiving a sample signal representative of the amplifier output signal, said power detector means rectifying said sample signal to thereby provide for a DC output signal;
• variable coupling means coupled between the output of said amplifier and said power detector means for providing the sample signal to said power detector means, said variable coupling means receiving said amplifier output signal and an isolation control signal and providing in response a variable amount of isolation between the amplifier output and said power detector means, such that the sample signal provided therefrom is a function of the power level of the output;
• control means for providing said isolation control signal, said isolation control signal controlling the amount of isolation provided for a given range of output signals;
• comparator means for comparing the DC output of said power detector means with a reference voltage to obtain an error voltage;
• adjustment means for adjusting the output of said power amplifier in relation to error voltage so as to maintain a desired amplifier output signal;
• and
• means for storing a plurality of isolation voltages, each isolation voltage being representative of a given range of amplifier output signals.

A method for providing automatic power output control for an amplifier over a wide dynamic range, said method comprising:

• receiving an input signal;
• amplifying said input signal with a power amplifier to provide an RF power output signal;
• coupling the output of said power amplifier to a variable coupling network which receives said output signal and an isolation control signal and provides in response a variable amount of isolation therein, said variable coupling network further providing a sample signal therefrom;
• rectifying the sample signal provided from said variable coupling network with a power detector to thereby provide a DC power signal;
• comparing the DC power signal with a reference voltage to obtain an error voltage;
• adjusting said power amplifier in relation to said error voltage so as to maintain a desired power output signal;
• storing a plurality of isolation voltages, each isolation voltage being representative of a given range of amplifier output signals;
• and
• providing one of said isolation voltages as the isolation control signal.