Amplifiers – With semiconductor amplifying device – Including gain control means
Patent
1987-10-09
1989-08-22
Mottola, Steven
Amplifiers
With semiconductor amplifying device
Including gain control means
330129, H03G 320
Patent
active
048599646
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an apparatus and a method for automatic gain control of a signal. More particularly, the apparatus and method relate to adjustment of gain so as to maintain an output signal between upper and lower limits.
BACKGROUND OF THE INVENTION
Known prior art gain control circuits have been implemented exclusively with analog devices, by combining both analog circuits and digital circuits or with only digital electronics. Known prior art gain control circuits detect a single characteristic parameter of the input signal which is to be adjusted. The selected parameter may include the main valve, effective value or peak value of the signal.
Where it is desirable, because of downstream processing, to use a gain control circuit which includes digital elements problems have been encountered in processing analog input signals having large dynamic ranges. The problems arise out of the fact that the digital circuitry, which might be implemented in part as a microprocessor, is usually organized to have a predetermined digital word length.
If the dynamic range of the analog signal is too large, it will at times exceed the predetermined digital word length. When this happens, it is necessary to resort to multiple word arithmetic which can be slower and more complicated than single word arithmetic.
In some applications, the input analog signal to be processed may lie within a relatively narrow, predetermined frequency range and have an overall known wave form the dynamic range of which varies. At times, the signal which is intended to be processed may be distorted due to noise superimposed thereon.
If the amplitude of the noise exceeds that of the signal to be processed, it will have an undesired effect on the operation of the automatic gain control circuitry. Hence, in addition to being able to deal with an input signal of a varying dynamic range, it is also desirable to be able to filter the signal prior to carrying out the gain control-related processing.
SUMMARY OF THE INVENTION
In accordance with the invention, a method of processing any input analog signal having variable values and of automatically adjusting the gain of a corresponding amplifier system is provided. The method includes the steps of amplifying the input signal by a predetermined value of gain.
Subsequent to the amplifying step, the signal is then digitized. The digitized values of the analog signal are then stored.
A determination is then made as to whether or not the digitized values are increasing or decreasing. If the digitized values are increasing, those values are compared to an upper predetermined threshold. If the maximum digital values exceed the predetermined threshold, the gain is subsequently reduced incrementally. If the digitized values are decreasing, they are compared to a predetermined lower threshold. If the maximum digitized values fall below the lower threshold, the gain of the system is subsequently incrementally increased.
In addition, if desired, the digitized values can be filtered so as to remove unwanted components therefrom prior to the determining step. The filtering step can include determining of frequency value for the unwanted component and removing the unwanted component from the digitized values.
A system for processing an input analog signal includes a variable gain amplifier for amplifying the input analog signal by a predetermined gain value. Analog-to-digital converter circuitry is provided for digitizing the amplified analog signal.
A memory is provided for storing the digitized values received from the analog-to-digital converter. Control circuitry is provided for determining if the digitized values are increasing or decreasing.
The control circuitry can also compare the values of the digitized signal to an upper threshold if that signal is increasing. The gain adjusting circuitry is provided for subsequently, incrementally reducing the gain value if a selected digitized maximum value exceeds the upper threshold.
The control circuitry also compares the values of t
REFERENCES:
patent: 4297527 (1981-10-01), Pate
patent: 4546326 (1985-10-01), Van Uffelen et al.
patent: 4553104 (1985-11-01), Olsen
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