Abstract: A successive approximation A/D having dual comparators for allowing a larger range of analog input signals to be converted into digital form. One comparator is an N-channel device, and the other comparator is a P-channel device. The A/D switches to either the N-channel device or the P-channel device based upon whether the first two comparisons the determine the most-significant bit and the next-most significant bit are a "11", in which the N-channel device is selected, or anything else, in which the P-channel device is selected. Switching circuitry is included to output the proper comparator based on these two comparisons.Control circuitry is also provided to allow for successive conversions using only a single address read.

Abstract: A system for bar code reading and scanning is provided having automatic gain control for accurate reading of bar codes over a range of distance. An amplifier within the system provides a plurality of selectable amplification gain levels for increasing the size of the signal received by a digitizing element. A processor is programmed to select the gain level. The system has a light source, preferably a laser diode, and a laser diode circuit, which provides accurate setting by the processor of the laser optical power output. The laser diode is calibrated according to each selected gain level of the amplifier such that the system can scan within a desired range of distances from the system to a bar code. The system successively scans a bar code, with each scan being at a different amplification level. In the alternative, a signal size detector provides a signal representative of the size of the signal to the digitizer.

Abstract: A resolution enhancer circuit provides an increased resolution capability for an A/D converter. The resolution enhancer circuit receives as input an analog input signal having a range greater than the effective range of the A/D, and prescales the input signal to a range that is within the common mode range of op amps used within the resolution enhancer circuit. The input signal can also have a range much less than the effective range of the A/D, and then it would be increased by the prescaler to be within an operable range of the A/D. The prescaled signal is provided to a sampling circuit, which samples the prescaled signal at times determined to be near-saturation conditions of the A/D. A magnified difference between the prescaled signal and the sampled signal, biased to the sampled signal, is then input to the A/D, which determines a number of A/D counts based on that value.

Abstract: A system for use in a bar code processing system using a combination of a first derivative signal and a second derivative signal to determine the bar edge. The predominant signal in determining the edge is the second derivative signal. A zero-cross of the second derivative signal occurs at the bar edge. The first derivative signal is used to qualify the point in time in the second derivative signal for which a zero-cross is examined the system is particularly suited for near filled operation.

Abstract: An optical scanner unit has a window which transmits light from inside the scanner to a target, for example, a bar code, and receives light from a target into the scanner. The window is tilted at Brewster's angle to permit light from inside the scanner to exit the scanner without "exit reflection" of light off the interior of the window. The window also permits light returned from the scanned target to enter the scanner and be sensed by a photodetector therein. The same window may be used for light transmitted to the photodetector and from the light source. The window is disposed at Brewster's angle relative to the scanning beam at the center of scan, and is close to Brewster's angle over the entire scan.

Abstract: A control system for a scanning motor that may operate at constant power, which has a control circuit including an H-Bridge connected across the drive coil of the motor. The control circuit operates under microprocessor control for digitally generating selected high current and a low current thresholds, which can be changed to enable the scanning motor to be operative over a large range (e.g. 3.3 v to 8 v) of supply voltage and to control the arc over which the motor oscillates and, therefore, the scan angle of an optical beam which scans a bar code. The control circuit turns the current to the drive coil on and off when the high and low thresholds are reached thereby varying the current which the motor draws which determines the scan angle and scan rate and average current draw, which may be maintained constant for constant power consumption.

Abstract: A D/A converter having a bias circuit that supplies a well-compensated gate voltage to a weighted current source part of the D/A converter, so that any changes in component characteristics due to the manufacturing of the components making up the D/A converter or due to temperature variations in the D/A converter are compensated for to output a correct analog voltage. The bias circuit comprises an amplifier and a p-type FET, where the drain of the p-type FET is fed back to a non-inverting input of the amplifier, and a reference voltage is applied to an inverting input of the amplifier. The bias circuit operates in a negative feedback condition, such that the non-inverting input is kept as close to the reference voltage as possible. A first resistor is connected to the drain of the p-type FET, to determine the current at the drain of the p-type FET. The weighted current source is made up of FETs having similar operating characteristics as the p-type FET of the bias circuit.

Abstract: A successive approximation A/D having dual comparators for allowing a larger range of analog input signals to be converted into digital form. One comparator is an N-channel device, and the other comparator is a P-channel device. The A/D switches to either the N-channel device or the P-channel device based upon whether the first two comparisons determine the most-significant bit and the next-most significant bit are a "11", in which the N-channel device is selected, or anything else, in which the P-channel device is selected. Switching circuitry is included to output the proper comparator based on these two comparisons.Control circuitry is also provided to allow for successive conversions using only a single address read. A one-half clock cycle reset occurs at the start of every MSB comparison for every n-bit read, and this reset goes to every component in the A/D except the latch for the LSB, which must be held for at least one more clock cycle before since it has not yet been output to the data bus as yet.

Abstract: An amplifier circuit provides wide bandwidth low noise performance by minimizing the effect of a pole created by the feedback resistor and the capacitance of the input device, such as a photodiode. This is accomplished by shifting the dominant pole to higher frequencies in the amplifier disclosed. A first amplifier stage receives a signal from an input device, such as the photodiode, and feedback from a second amplifier stage. The first amplifier stage is connected to the second amplifier stage such that a lower gain stage is employed to eliminate the phase shift which occurs if the amplifier alone is used in open loop form. The output of the low gain stage is provided to a second amplifier stage with associated gain setting components such that the dominant pole of the overall amplifier is shifted to a higher frequency, typically two decades higher than available from the single stage open loop amplifier.

Abstract: A video brightness control system for high performance CRT displays including a buffer amplifier for receiving high speed video information and applying it to a gain control variable resistor serving as a contrast control. An ambient light sensor drives a nonlinear amplifier to provide an ambient light signal which is in proportion to the logarithm of the ambient light level over a wide range. A manual brightness control potentiometer is adjustable to provide a constant brightness signal. The video information signal, the ambient light signal, and the manual brightness control signal are added together by a summing device, with the resultant signal approximating a logarithmic characteristic. The output of the summing device is applied to a gamma correction amplifier which drives a video driver amplifier, the video amplifier, in turn, drives the CRT.