EER modulator with power amplifier having feedback loop providing soft output impedance

An amplifier comprising:

• a divider circuit for dividing an incoming signal into a low frequency amplitude modulation envelope signal and a phase portion;
• a first RF amplifier for amplifying said phase portion, said first RF amplifier having a bias supply input;
• a modulator connected to receive said envelope signal for furnishing a modulated bias supply to said bias supply input of said first RF amplifier, said modulator comprising:
• a high frequency operational amplifier for amplifying a higher frequency portion of said envelope signal and a power amplifier for amplifying a lower frequency portion of said envelope signal, said power amplifier having an output current control input and an output current monitoring port;
• a feedback control loop having first and second inputs and a control output connected to said output current control input of said power amplifier, said first and second inputs connected respectively to said envelope signal and said output current monitoring port of said power amplifier, said feedback control loop comprising means for producing at said control output a signal which is a function of a difference between said envelope signal and the output current at said monitoring port of said power amplifier, whereby said feedback control loop controls the output current of said power amplifier so as to minimize said difference.

In an envelope elimination and restoration (EER) amplifier, an EER modulator comprising:

• a high frequency amplifier having an input coupled to receive an envelope signal and an output having an output impedance;
• a power amplifier having a first gain, outputs of said high frequency amplifier and said power amplifier being coupled to an EER modulator output node;
• a feedback control loop having a first input coupled to receive said envelope signal and a second input coupled to receive an output signal of said power amplifier, said feedback control loop providing an input to said power amplifier to minimize a difference between the output of said power amplifier and said envelope signal;
• said feedback control loop having a first gain and said power amplifier having a second gain, said first and second gains being such that the output impedance of the combination of said power amplifier and feedback control loop does not exceed said output impedance of said high frequency amplifier by more than a factor of ten.