Dual band cellular phone with two power amplifiers and power control circuit therefore

A transmitter for a cellular phone comprising an antenna and being operable at a first radio frequency band and a second radio frequency band, said transmitter comprising:

• a first power amplifier, said first power amplifier having a first input for a first signal at said first radio frequency band, a second input for a first control signal and a first output for an amplified first signal, said first output being connectable to said antenna;
• a second power amplifier, said second power amplifier having a third input for a second signal at said second radio frequency band, a fourth input for a second control signal and a second output for an amplified second signal, said second output being connectable to said antenna;
• and
• a control module, said control module being associated with said first and second outputs to receive a portion of one of said amplified first and second signals, and generating one of said first and second control signals to control one of said first and second power amplifiers, said control signal being a function of one of said first and second amplified signals and a reference signal, said control module comprising:
• a detector, said detector having an input for a portion of an amplified signal derived from one of said amplified first and second signals, and an output which, responsive to said input, provides a detection signal corresponding to said portion;
• a comparator having an input which receives said reference signal and having an input which receives said detection signal, said comparator generating an error signal corresponding to a difference between said reference signal and said detector signal;
• and
• a shaping circuit, said circuit weighting said error signal in accordance with a predetermined desired power characteristic to generate said control signal which accounts at least in part, for nonlinear amplification characteristics of said power amplifiers.

A control module for a dual band transmitter in a cellular phone, said dual band transmitter comprising first and second power amplifiers, said module comprising:

• a logarithmic detector, said detector having an input which receives a portion of a signal derived from an amplified RF signal, and an output, which in response to said input, provides a detection signal corresponding to said signal portion;
• a differential amplifier, said differential amplifier having a reference input which receives a reference signal and having a detection signal input which receives said detection signal, said amplifier generating an error signal corresponding to a difference between said reference signal and said detector signal;
• an integrator, said integrator integrating said error signal and generating an integrated error signal;
• and
• a shaping circuit, said circuit weighting said integrated error signal in accordance with a predetermined power level characteristic to generate said control signal which accounts, at least in part, nonlinear amplification characteristics of said power amplifiers.

A method for controlling an output power level of a dual band cellular phone, comprising the steps of:

• providing a dual band transmitter comprising a single control module, and first and second power amplifiers which are coupled to an antenna;
• activating one of said first and second power amplifiers;
• feeding an RF signal to said activated power amplifier;
• amplifying said RF signal with said activated power amplifier;
• feeding said amplified RF signal to said antenna;
• coupling a portion from said amplified RF signal;
• feeding said portion to said single control module;
• detecting said portion and generating a detector signal corresponding to said portion;
• comparing said detector signal with a reference signal to generate an error signal corresponding to a difference between said reference signal and said detector signal;
• weighing said error signal in accordance with a predetermined desired power characteristic to generate a control signal which accounts, at least in part, for nonlinear amplification characteristics of said power amplifiers;
• and
• feeding said control signal to the activated power amplifier to control the activated power amplifier to provide an amplified RF signal which is in accordance with a desired signal characteristic defined by the reference signal.

A cellular phone for a mobile communications system, said phone being operable at a first radio frequency band and a second radio frequency band comprising a dual band transmitter and an antenna, said dual band transmitter comprising:

• a first power amplifier, said first power amplifier having a first input for a first signal at said first radio frequency band, a second input for a first control signal and a first output for an amplified first signal, said first output being connectable to said antenna;
• a second power amplifier, said second power amplifier having a third input for a second signal at said second radio frequency band, a fourth input for a second control signal and a second output for an amplified second signal, said second output being connectable to said antenna;
• and
• a control module, said control module being associated with said first and second outputs to receive a portion of one of said amplified first and second signals, and generating one of said first and second control signals to control one of said first and second power amplifiers, said control signal being a function of one of said first and second amplified signals and a reference signal, said control module comprising:
• a logarithmic detector having an input for a portion of an amplified signal derived from one of said amplified first and second signals, and an output for a detection signal indicative of the power level of said amplified signal, wherein said logarithmic detector comprises a first signal path and a second signal path, said first and second signal paths being joined at an input of the logarithmic detector and at a summing stage associated with an output of the logarithmic detector, said first signal path comprising a serial arrangement of a first number of amplifiers and an equal number of detectors, each detector being interconnected between an output of an amplifier and an input of the summing stage, said second signal path comprising a serial arrangement of an attenuator, a second number of amplifiers and an equal number of detectors, each detector being interconnected between an output of an amplifier and an input of the summing stage, said attenuator being interconnected between the input of the logarithmic detector and a first amplifier of the second signal path;
• a comparator having an input which receives said reference signal and having an input which receives said detection signal, said comparator generating an error signal corresponding to a difference between said reference signal and said detection signal;
• and
• a shaping circuit, said circuit weighting said error signal in accordance with a predetermined desired power characteristic to generate said control signal which accounts, at least in part, for nonlinear amplification characteristics of said power amplifiers.

A transmitter for a cellular phone comprising an antenna and being operable at a first radio frequency band and a second radio frequency band, said transmitter comprising:

• a first power amplifier, said first power amplifier having a first input for a first signal at said first radio frequency band, a second input for a first control signal and a first output for an amplified first signal, said first output being connectable to said antenna;
• a second power amplifier, said second power amplifier having a third input for a second signal at said second radio frequency band, a fourth input for a second control signal and a second output for an amplified second signal, said second output being connectable to said antenna;
• and
• a control module, said control module being associated with said first and second outputs to receive a portion of one of said amplified first and second signals, and generating one of said first and second control signals to control one of said first and second power amplifiers, said control signal being a function of one of said first and second amplified signals and a reference signal, said control module comprising:
• a logarithmic detector, said detector having an input for a portion of an amplified signal derived from one of said amplified first and second signals, and an output which, responsive to said input, provides a detection signal corresponding to said portion, wherein said logarithmic detector comprises a first signal path and a second signal path, said first and second signal paths being joined at an input of the logarithmic detector and at a summing stage associated with an output of the logarithmic detector, said first signal path comprising a serial arrangement of a first number of amplifiers and an equal number of detectors, each detector being interconnected between an output of an amplifier and an input of the summing stage, said second signal path comprising a serial arrangement of an attenuator, a second number of amplifiers and an equal number of detectors, each detector being interconnected between an output of an amplifier and an input of the summing stage, said attenuator being interconnected between the input of the logarithmic detector and a first amplifier of the second signal path;
• a comparator having an input which receives said reference signal and having an input which receives said detection signal, said comparator generating an error signal corresponding to a difference between said reference signal and said detector signal;
• and
• a shaping circuit, said circuit weighting said error signal in accordance with a predetermined desired power characteristic to generate said control signal which accounts at least in part, for nonlinear amplification characteristics of said power amplifiers.

A control module for a dual band transmitter in a cellular phone, said dual band transmitter comprising first and second power amplifiers, said module comprising:

• a logarithmic detector, said detector having an input which receives a portion of a signal derived from an amplified RF signal, and an output, which in response to said input, provides a detection signal corresponding to said signal portion, wherein said logarithmic detector comprises a first signal path and a second signal path, said first and second signal paths being joined at an input of the logarithmic detector and at a summing stage associated with an output of the logarithmic detector, said first signal path comprising a serial arrangement of a first number of amplifiers and an equal number of detectors, each detector being interconnected between an output of an amplifier and an input of the summing stage, said second signal path comprising a serial arrangement of an attenuator, a second number of amplifiers and an equal number of detectors, each detector being interconnected between an output of an amplifier and an input of the summing stage, said attenuator being interconnected between the input of the logarithmic detector and a first amplifier of the second signal path;
• a differential amplifier, said differential amplifier having a reference input which receives a reference signal and having a detection signal input which receives said detection signal, said amplifier generating an error signal corresponding to a difference between said reference signal and said detector signal;
• an integrator, said integrator integrating said error signal and generating an integrated error signal;
• and
• a shaping circuit, said circuit weighting said integrated error signal in accordance with a predetermined power level characteristic to generate said control signal which accounts, at least in part, nonlinear amplification characteristics of said power amplifiers.