Amplifiers – With control of power supply or bias voltage – With control of input electrode or gain control electrode bias
Patent
1987-10-09
1989-03-07
Wan, Gene
Amplifiers
With control of power supply or bias voltage
With control of input electrode or gain control electrode bias
330 9, H03G 320, H03F 102
Patent
active
048109738
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a method of compensating the offset voltage in a variable-gain amplifier.
Variable-gain amplifiers are employed for example in focus-and tracking-control loops in the optical scanning systems of compact-disk players. The wanted signals--audio or video signals stored in circular or spiral tracks on the disk for example--employed in compact-disk players are read out with an optical system. The optical system consists as a rule of a system of lenses that are axially displaced by the focus-control loop in such a way that the focus of the lens system rests against the disk. This method of control, which is basically similar to adjusting the image in a telescope, is called focussing. To allow the optical system to read the wanted signals off the disk satisfactorily it is necessary for the focus-control loop to be constantly adjusting the focus. Since even slight deviations in sharpness can lead to errors in reading the wanted signals stored on the disk, the variable-gain amplifier offset voltage cannot be too high, and it must accordingly be compensated.
SUMMARY OF THE INVENTION
The object of the invention is accordingly a method of compensating the offset voltage of a variable-gain amplifier.
This object is attained in accordance with the invention in that, in order to measure the offset-compensation voltage, the output terminal of the variable-gain amplifier is disconnected from the control-loop controls, in that the level of offset-compensation voltage is stored, in that, once the level of offset-compensation voltage has been detected and stored, the output terminal is reconnected to the control-loop controls, and in that the stored offset-compensation voltage is applied to the input terminal of the variable-gain amplifier.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are diagrams of the circuitry employed to carry out the method in accordance with the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The method in accordance with the invention will now be described with reference to the circuitry illustrated in FIG. 1.
The output terminal of the variable-gain amplifier RV illustrated in FIG. 1 is connected to the input terminal of an analog-to-digital converter AD and to one contact of a variable switch S, the other contact of which is connected to controls SG. The signal F that governs controls SG is at the input terminal of variable-gain amplifier RV. The output terminal of analog-to-digital converter AD is connected to one input terminal E1 of a control circuit ST. One output terminal A1 of control circuit ST is connected to the input terminal of an up-and-down counter Z, the output terminal of which is connected to the input terminal of a digital-to-analog converter DA. The output terminal of digital-to-analog converter DA is feedbacked to the input terminal of variable-gain amplifier RV. The offset reference voltage is applied to another input terminal E2 of control circuit ST. Another output terminal A2 of control circuit ST is connected to the control input terminal of variable switch S.
The operation of the circuitry that is illustrated in FIG. 1 and that can be installed in a compact-disk player for example will now be described.
When the compact-disk player is turned on, control circuit ST opens variable switch S and hence the focus-control loop. While the focus-control loop is open, the analog offset voltage at the output terminal of variable-gain amplifier RV is supplied in digital form through analog-to-digital converter AD to control circuit ST, wherein the offset voltage is compared with the offset reference voltage, which is usually zero. Control circuit ST releases counting pulses to up-and-down counter Z as long as the offset voltage at the output terminal of variable-gain amplifier RV does not equal the zero offset reference voltage. The count at the output terminal of counter Z is converted into an analog voltage in digital-to-analog converter DA. The analog voltage is feedbacked to the input terminal of variable-gain ampli
REFERENCES:
patent: 4229703 (1980-10-01), Bustin
patent: 4494551 (1985-01-01), Little, III et al.
Kash, R., "Building Quality Analog Circuits with C-MOS Logic Arrays", Electronics, Aug. 11, 1981.
Deutsche Thomson-Brandt GmbH
Fogiel Max
Wan Gene
LandOfFree
Method of compensating the offset voltage in a variable gain amp does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of compensating the offset voltage in a variable gain amp, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of compensating the offset voltage in a variable gain amp will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1671190