Method and circuit for voice automatic gain control

In an amplifier using automatic gain control, a system for minimizing distortion of an output signal from said amplifier in response to wide level variations in a source signal, comprising:

• means for monitoring the source signal level;
• means for calculating an initial gain factor required to modify the source signal level according to said automatic gain control;
• and
• means for gradually modifying the initial gain factor to within a preselected band of allowable values when the source signal is monitored above a preselected minimum level and the initial gain factor is monitored above said preselected band;
• means for periodically sampling said source signal to detect instantaneous power levels at particular times;
• and
• means for calculating a windowed average power level at a particular point in time by averaging a predetermined number of instantaneous power levels detected during a predetermined period of time.

In an amplifier using automatic gain control, a method of maintaining an output signal from said amplifier at a preselected, substantially constant level, said method comprising the steps of:

• calculating an initial gain factor from a source signal according to said automatic gain control;
• establishing a modified gain factor from said initial gain factor, the establishing step including the substeps of:
• setting said initial gain factor equal to a lower limit of a preselected band of allowable values when said source signal is below a preselected minimum level, said step of setting thereby producing said modified gain factor;
• moving said initial gain factor to within said preselected band when said source signal is above said preselected minimum level and said initial gain factor is above said preselected band, said step of moving thereby producing said modified gain factor;
• and
• making said modified gain factor equal to said initial gain factor when said initial gain factor is within or below said preselected band;
• and
• multiplying an input signal by said modified gain factor.

In an amplifier using automatic gain control, a circuit for maintaining an output signal from said amplifier at a pre-selected, substantially constant level, comprising:

• means for calculating an initial gain factor from a source signal according to said automatic gain control;
• means for changing said initial gain factor to a modified gain factor, said changing means further comprising:
• means for setting said initial gain factor equal to a lower limit of a preselected band of allowable values when said source signal is below a preselected minimum level, said setting means thereby producing said modified gain factor;
• means for moving said initial gain factor to within said preselected band when said source signal is above said preselected minimum level and said initial gain factor is above said preselected band, said moving means thereby producing said modified gain factor;
• and
• means for making said modified gain factor equal to said initial gain factor when said initial gain factor is within or below said preselected band;
• and
• means for multiplying an input signal by said modified gain factor.

In an amplifier using automatic gain control, a method of minimizing distortion of an output signal from said amplifier in response to wide level variations in a source signal, said method comprising the steps of:

• monitoring the source signal level, said monitoring step including the substeps of:
• periodically sampling said source signal to detect levels thereof at predetermined times;
• identifying a predetermined time window in said sample stream;
• and
• averaging said sample levels within said time window to determine a windowed average level;
• calculating an initial gain factor as a predetermined function of the windowed average level;
• and
• at a predetermined controlled rate of change, modifying the initial gain factor to within a preselected band of allowable values when the source signal is monitored above a preselected minimum level and the initial gain factor is monitored above said preselected band, said predetermined controlled rate of change being a function of the value of the initial gain factor.

In an amplifier using automatic gain control, a system for minimizing distortion of an output signal from said amplifier in response to wide level variations in a source signal, the system comprising:

• means for monitoring the source signal level, said monitoring means including:
• means for periodically sampling said source signal to detect levels thereof at predetermined times;
• means for identifying a predetermined time window in said sample stream;
• and
• means averaging said sample levels within said time window to determine a windowed average level;
• means for calculating an initial gain factor as a predetermined function of the windowed average level;
• and
• means for modifying, at a predetermined controlled rate of change, the initial gain factor to within a preselected band of allowable values when the source signal is monitored above a preselected minimum level and the initial gain factor is monitored above said preselected band, said predetermined controlled rate of change being a function of the value of the initial gain factor.