Back to results
US 5,350,908 AGranted
Automatic gain control circuit having disturbance cancellation capabilities
AssigneeAllen-Bradley Company, Inc.
InventorRichard D. Bechtel
Life of this patent
Estimating the term…
Abstract
A system for filtering electrical signals and cancelling large amplitude disturbance events contaminating such signals which might otherwise interfere with these signals being further processed. The system includes a disturbance filter which is operative for identifying disturbance events and passing an inverted signal corresponding solely to these events to a summing junction for use in cancelling these events as they occur. In the preferred embodiment this system is adapted for use in a bar code reader.
Claims18
An automatic gain control circuit having disturbance cancellation capabilities, comprising:
- a variable-gain amplifier having an input for receiving an input signal to be amplified for gain control purposes, an output for supplying a gain-controlled output signal and a gain control terminal;
- a rectifier having its input connected to the output of said variable-gain amplifier for providing a rectified signal based on the output signal of said amplifier;
- a sampling network for generating a filtered output signal from said rectified signal;
- an error amplifier having an input coupled for receiving said filtered output signal of said sampling network and an output connected to said gain control terminal, said error amplifier adapted for amplifying the output of said sampling network based on a difference with a reference signal and applying the resulting error signal to said gain control terminal;
- a differencing amplifier having a first input coupled for receiving said rectified signal, a second input connected to a level switching network and an output coupled to said sampling network for supplying a disturbance cancellation signal for combination with said rectified signal;
- means for clamping the first input to said differencing amplifier to a fixed voltage level for all signal levels at said input below said voltage level;
- and
- a level switching network connected to the second input to said differencing amplifier for applying a voltage signal to said second input and for shifting the level of this voltage signal between said fixed voltage level and ground based on the level of said rectified signal.
5 more elements
A bar code reader, comprising:
- a photodiode for detecting light signals encoded with bar code information;
- a variable-gain amplifier for amplifying signals from said photodiode having a gain control terminal and an output for supplying an amplified bar code signal;
- a rectifier for converting said amplified bar code signal from said variable-gain amplifier to a rectified signal;
- a sampling network for filtering said rectified signal from said rectifier to generate a sampled signal;
- an error amplifier for amplifying said sampled signal from said network and applying the resulting error signal to said gain control terminal;
- means for detecting disturbance events in said rectified signal as they occur, inverting these disturbance signals to form inverted signals during such events and summing these inverted signals with the rectified signal from said rectifier before this signal is applied to said sampling network in order to cancel the disturbance events in said rectified signal from said rectifier;
- and
- means for decoding said bar code signal to identify said bar code information.
5 more elements
An automatic gain control circuit having disturbance cancellation capabilities, comprising:
- a variable-gain amplifier having an input for receiving an input signal to be amplified for gain control purposes, an output for supplying a gain-controlled output signal and a gain control terminal;
- a rectifier having its input connected to the output of said variable-gain amplifier for providing a rectified signal based on the output signal of said amplifier;
- a sampling network for generating a filtered output signal from said rectified signal;
- an error amplifier having an input coupled for receiving said filtered output signal of said sampling network and an output connected to said gain control terminal, said error amplifier adapted for amplifying the output of said sampling network based on a difference with a reference signal and applying the resulting error signal to said gain control terminal;
- a differencing amplifier having a first input coupled for receiving said rectified signal, a second input connected to a level switching network and an output coupled to said sampling network for supplying an output signal in which major disturbance events have been cancelled to said sampling network;
- an inverting amplifier having an input connected to said rectifier for receiving said rectified signal and an output connected to said first input of said differencing amplifier;
- means for clamping the first input to said differencing amplifier to a fixed voltage level for all signal levels below said voltage level;
- and
- a level switching network connected to the second input to said differencing amplifier for applying a voltage signal to said second input and for shifting the level of this voltage signal between said fixed voltage level and ground based on the level of said rectified signal.
6 more elements
A disturbance filter for processing signals containing large amplitude disturbance events, comprising:
- a differencing amplifier having a first input coupled for receiving an input signal, a second opposite polarity input connected to a level switching network and an output for supplying an output signal including only disturbance events;
- means for clamping coupled to said first input to said differencing amplifier for clamping this input to a fixed voltage level when said input signal is below said fixed voltage level;
- and
- a level shifting network coupled to the second input of said differencing amplifier for supplying a voltage signal to said second input and shifting the level of this voltage signal from said fixed voltage level to ground whenever said input signal exceeds said fixed voltage level and from ground to said fixed voltage level whenever said input signal is below said fixed voltage level.
1 more element
A bar code reader comprising:
- a photodiode positioned for receiving light signals containing bar code information and generating an electrical signal based on these light signals;
- a differentiater for generating a differentiated signal as a function of the rate of change of said electrical signal;
- a peak detector for generating a peak identification signal based on said differentiated signal;
- a rectifier for generating a rectified signal from said differentiated signal;
- means for generating a disturbance cancellation signal from said rectified signal;
- a summing junction for combining said rectified signal and said cancellation signal to generate a combined signal which is free from large amplitude disturbance events;
- a sampling network for generating a filtered signal by low pass filtering said combined signal;
- a window comparator for generating threshold detection signals by comparing the amplitude of said rectified signal to thresholds set as a function of said filtered signal;
- and
- correlation circuitry for detecting bar code signals by processing and correlating said peak identification and threshold detection signals.
7 more elements
Dependencies are inferred from the claim text.