Gain control circuit and method for providing gain control of a variable amplifier using a pilot signal
AssigneeMotorola, Inc.
InventorMark Brian Anderson
Life of this patent
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Abstract
The present invention provides for a gain control circuit (10) and method for providing gain control of a variable amplification circuit (16) using a pilot signal. A pilot signal is added to the received signal. The pilot signal has at least a minimum signal level which when added to the signal received insures the sampled input signal has a level above the point where offset or low power errors are experienced. Preferably the pilot signal will be a sinusoidal signal having a frequency within the operational bandwidth of the amplifier (16), but outside the frequency range of the input signal.
Claims16
A gain control circuit comprising:
- a received signal input for receiving an input signal to be amplified;
- a pilot signal injector coupled to said received signal input for adding a pilot signal to the input signal;
- a variable amplification circuit coupled to said pilot signal injector for receiving the input signal with pilot signal added and producing an amplified output signal, and having a control input, the level of amplification dependent upon the value of the signal received at the control input;
- an input sampling circuit coupled to said pilot signal injector for sampling the input signal with pilot signal added;
- an output sampling circuit coupled to said variable amplification circuit for sampling the amplified output signal;
- and
- a control loop for receiving the sampled input signal with pilot signal added and the sampled amplified output signal, for producing a control signal coupled to the control input of the variable amplification circuit.
A method for providing gain control of a variable amplifier using a pilot signal comprising the steps of:
- receiving an input signal;
- adding a pilot signal to the input signal;
- amplifying the input signal with pilot signal added a variable amount, for producing an amplified output signal;
- sampling the input signal with pilot signal added;
- sampling the amplified output signal;
- comparing the sampled input signal with pilot signal added to the sampled amplified output signal, wherein the sampled input signal with pilot signal added is comprised primarily of the pilot signal portion of the sampled input signal with pilot signal, when the received portion of the signal level of the sampled input signal with pilot signal added falls below a predetermined threshold;
- and
- adjusting the variable amount of amplification in the step of amplifying the input signal with pilot signal added, based on the result of the comparison between the sampled input signal with pilot signal added and the sampled amplified output signal.
Dependencies are inferred from the claim text.