Output level control circuit for use in RF power amplifier

An output level control circuit for use in a high frequency power amplifier responsive to a control signal having "on" and "off" periods in a recurrent cycle for amplifying an intermittent high frequency signal having a waveform corresponding to said control signal and supplying them to an antenna, comprising high frequency power extracting means for taking out part of the output of said high frequency power amplifier, and a high frequency detecting circuit responsive to the output of said extracting means and said control signal for generating a detection output representing the high of said waveform, wherein:

• said high frequency detecting circuit comprises detecting means supplied with said high frequency signal and generating an output representing the level of said high frequency signal;
• means for analog-to-digital (A/D) converting the output of said detecting means;
• signal accumulating means for accumulating the output of said A/D converting means corresponding to the output of said detecting means during each of said "off" periods and supplying the accumulated output of said A/D converting means at the beginning of the "on" period immediately following that "off" period;
• and
• means for subtracting the output of said signal accumulating means from the output of said A/D converting means in each of said recurrent cycles.

A high frequency detecting circuit, in an output level control circuit for use in a high frequency power amplifier responsive to a control signal having "on" and "off" periods in a fixed recurrent cycle for amplifying an intermittent high frequency signal having a waveform corresponding to said control signal and supplying them to an antenna, responsive to an extracted output from high frequency power extracting means, which takes out part of the output of said high frequency power amplifier, and said control signal for generating a detection output representing the height of said waveform and supplying that detection output to amplitude control means for controlling the amplitude of said high frequency power amplifier,

• said high frequency detecting circuit comprising:
• detecting means supplied with said high frequency signal and generating an output representing the level of said high frequency signal;
• and
• differential voltage generating means for generating, for each of said recurrent cycles, a voltage representing the difference between the output of said detecting means during one "on" period and the output of said detecting means during an "off" period immediately preceding said one "on" period.

A high frequency detecting circuit, in an output level control circuit for use in a high frequency power amplifier responsive to a control signal having "on" and "off" periods in a fixed recurrent cycle for amplifying an intermittent high frequency signal having a waveform corresponding to said control signal and supplying them to an antenna, responsive to an extracted output from high frequency power extracting means, which takes out part of the output of said high frequency power amplifier, and said control signal for generating a detection output representing the height of said waveform and supplying that detection output to amplitude control means for controlling the amplitude of said high frequency power amplifier, wherein:

• said high frequency detecting circuit comprises detecting means supplied with said high frequency signal and generating an output representing the level of said high frequency signal;
• means for analog-to-digital (a/D) converting the output of said detecting means;
• signal accumulating means for accumulating the output of said A/D converting means corresponding to the output of said detecting means during each of said "off" periods and supplying the accumulated output of said A/D converting means at the beginning of the "on" period immediately following that "off" period;
• and
• means for subtracting the output of said signal accumulating means from the output of said A/D converting means in each of said recurrent cycles.

An apparatus comprising:

• power amplifier means responsive to a first control signal for amplifying a high frequency signal to produce an amplified signal;
• high frequency power extracting means for taking out part of said amplified signal to produce an extracted signal;
• detecting means responsive to a second control signal having "on" and "off" periods in a recurrent cycle for detecting said extracted signal to produce, for each of said cycles, a control voltage, said detecting means including a detecting diode;
• means for placing the output of said detecting means at a prescribed voltage during said "off" period and supplying said detecting diode with a forward bias current having a magnitude corresponding to said prescribed voltage during said "on" period;
• and
• control circuit means responsive to said control voltage and to said control signal for producing and supplying said first control signal to said power amplifier.