Abstract: Apparatus and methods are provided for feedback circuitry in a power converter, the feedback circuitry including a first resistor coupled to a first node between a high switch and a low switch, a first capacitor in series with the first resistor, the first capacitor coupled to a second node, a first comparator having a positive terminal connected between the first resistor and the first capacitor and a negative terminal connected to a third node, the first comparator configured to compare a voltage at the positive terminal to a voltage at the negative terminal, wherein the feedback circuitry is configured to generate a ramp waveform at the positive terminal of the first comparator, an amplitude of the ramp waveform based on a time constant of the first resistor and the first capacitor.

Abstract: Apparatus and methods are provided for feedback circuitry in a power converter, the feedback circuitry including a first resistor coupled to a first node between a high switch and a low switch, a first capacitor in series with the first resistor, the first capacitor coupled to a second node, a first comparator having a positive terminal connected between the first resistor and the first capacitor and a negative terminal connected to a third node, the first comparator configured to compare a voltage at the positive terminal to a voltage at the negative terminal, wherein the feedback circuitry is configured to generate a ramp waveform at the positive terminal of the first comparator, an amplitude of the ramp waveform based on a time constant of the first resistor and the first capacitor.

Abstract: A switch mode power converter that precisely controls average switching current and operating frequency. The switching control operative in hysteretic average current mode control provides wide bandwidth operation without the need for slope correction. The switching converter ripple current is varied by a frequency comparator in response to a comparison of the switching frequency to a reference frequency. The ripple current is adjusted to obtain correlation between the operating switching frequency and the reference frequency. Peak current levels are precisely controlled and may be limited to prevent component stress levels from being exceeded. Current levels are continuously monitored with a current sense amplifier, or monitored with a high-gain low energy current sampler. Feedback loop independent line and load regulation is provided by continuous current monitoring, or by using variable slope charge and transfer voltage to pulse width converters when operating with a current sampler based system.

Abstract: A voltage to current converter that can provide multiple current sources at differing voltage levels using a single inductor, without the need to provide a current sense element, pass element, and wiring to provide feedback for load current regulation. A switching inductor current is regulated such that the average current supplied by the inductor is equal to a user determined set point or points for a set of multiplexed loads. The inductor current levels are sampled and stored, and the average current level for each load is determined based on the sampled current levels. The average current levels are compared to a current level set point or set point signals to determine an error signal for each load current. The error signal for each current is amplified and filtered to provide duty cycle control terms. The duty cycle control terms are converted to pulse width modulated control signals by a pulse width modulator.

Abstract: Power converters employing extrapolative conductance mode (ECM) control utilize periodic current sampling and employ an extrapolation method to determine charge pulse duration. In preferred embodiments, the operating frequency of the converter is altered in response to current sample perturbations to dissipate sub-harmonic oscillations associated with duty cycles of 50% or greater without the use of slope correction. High current monitor signal-to-noise ratios may be achieved in conjunction with low power losses, and a first order output filter response may be obtained for duty cycles greater than 50%.

Abstract: A switch mode power converter that precisely controls average switching current and operating frequency. The switching control operative in hysteretic average current mode control provides wide bandwidth operation without the need for slope correction. The switching converter ripple current is varied by a frequency comparator in response to a comparison of the switching frequency to a reference frequency. The ripple current is adjusted to obtain correlation between the operating switching frequency and the reference frequency. Peak current levels are precisely controlled and may be limited to prevent component stress levels from being exceeded. Current levels are continuously monitored with a current sense amplifier, or monitored with a high-gain low energy current sampler. Feedback loop independent line and load regulation is provided by continuous current monitoring, or by using variable slope charge and transfer voltage to pulse width converters when operating with a current sampler based system.

Abstract: A method for driving a resonant electromagnetically-actuated motor, such as those used to scan a light source for date reading applications, wherein drive current is applied when the back-EMF induced in the actuator coil is zero and has a specific slope, and that drive current is removed after the induced back-EMF voltage has changed by a predetermined constant value. The drive circuit will drive the motor across a scan angle which remains substantially constant regardless of changes in ambient temperature, changes in motor orientation, or externally applied forces.

Abstract: A method for driving a resonant electromagnetically-actuated motor, such as those used to scan a light source for date reading applications, is described, wherein (in the preferred embodiment) drive current is applied when the back-EMF induced in the actuator coil is zero and has a specific slope, and that drive current is removed after the induced back-EMF voltage has changed by a predetermined constant value. It is shown that this drive means will drive the aforementioned motor across a scan angle which remains substantially constant regardless of changes in ambient temperature, changes in motor orientation, or externally applied forces.

Abstract: A system and method for improving the accuracy of edge detection under high Inter-Symbol Interference, or ISI, conditions is disclosed. The amplified and filtered first derivative signal is offset by equal amounts in both directions to generate positive and negative offsets which serve as inputs to negative and positive peak detectors, respectively. The offset is determined by a fast adaptive peak detector provided by attenuating and AC-coupling the first derivative signal to the positive supply to drive a peak detector with a fairly short attack time, such that its output is nearly settled on the first peak of the first derivative signal, but having a decay time long enough to keep the threshold level approximately constant across the label. Peaks are qualified if the peak in question differs in amplitude from the previously qualified peak by the offset amount.

Abstract: A bar code scanner system includes a laser light source that periodically produces a light beam that is swept across a bar code label. The laser light source is periodically turned "on" and "off" according to a duty cycle. A detector produces a first electric signal representative of received bar code label reflected light and ambient light when the laser light source is on, and produces a second electric signal representative of received ambient light when the light source is "off". A demodulator circuit, coupled to the detector, provides a first gain to the first electric signal and provides a second gain to the second electric signal. The gains applied are selected such that the signal and signal component produced solely as a result of the ambient light will significantly cancel out one another when the signals are combined. A filter, coupled to the demodulator circuit, receives the electric signals from the demodulator circuit and reduces out-of-band signal components such as noise.

Abstract: A bar code scanner system includes a laser light source that periodically produces a light beam that is swept across a bar code label. The laser light source is periodically turned "on" and "off" according to a duty cycle. A detector produces a first electric signal representative of received bar code label reflected light and ambient light when the laser light source is on, and produces a second electric signal representative of received ambient light when the light source is "off". A demodulator circuit, coupled to the detector, provides a first gain to the first electric signal and provides a second gain to the second electric signal. The gains applied are selected such that the signal and signal component produced solely as a result of the ambient light will significantly cancel out one another when the signals are combined. A filter, coupled to the demodulator circuit, receives the electric signals from the demodulator circuit and reduces out-of-band signal components such as noise.

Abstract: A system for bar code reading and scanning is provided having automatic bar code signal size control. In the first embodiment of the system, a processor selects on successive scans of a bar code one of a plurality of different optical power levels from a laser diode which provides a light beam illuminating the bar code. This selection is responsive to the size of the signal from a photo-detector which receives returned light from the bar code during scanning. The signal size is detected by a signal size detecting circuit, and is measured by the processor during scanning. In a second embodiment of the system, the processor calculates an optical power level after every two consecutive scans across the bar code. The laser power level is calculated differently for alternative scans occurring in different orders (even or odd counting from the first scan).

Abstract: In order to set the output optical power of a laser diode precisely and under digital control without expensive digital to analog conversion devices, a digital controller provides a sequence of pulses. A capacitor is charged by these pulses to produce a control voltage which controls the current through the laser diode via an operational amplifier driver stage. The output power obtained from the laser as detected by a photodetector, which is optically coupled to the laser and may be packaged therewith, is monitored by the computer so as to determine the rate at which laser power changes and indirectly at the rate at which the capacitor charges. This rate may vary depending upon environmental conditions and manufacturing tolerances. Based upon the charging rate, a pulse is generated and used to either provide additional charge or to charge the capacitor to the voltage corresponding to the desired optical power output.

Abstract: In order to set the output optical power of a laser diode precisely and under digital control without expensive digital to analog conversion devices, a digital controller provides a sequence of pulses. A capacitor is charged by these pulses to produce a control voltage which controls the current through the laser diode via an operational amplifier driver stage. The output power obtained from the laser as detected by a photodetector, which is optically coupled to the laser and may be packaged therewith, is monitored by the computer so as to determine the rate at which laser power changes and indirectly at the rate at which the capacitor charges. This rate may vary depending upon environmental conditions and manufacturing tolerances. Based upon the charging rate, a pulse is generated and used to either provide additional charge or to charge the capacitor to the voltage corresponding to the desired optical power output.

Abstract: A system for bar code reading and scanning is provided having automatic bar code signal size control. The scanner includes a processor which calculates, in response to a signal power level of the symbol which has been read, a first optical power level when the beam is scanned in a first direction and a second optical power output level when the beam is scanned in a second direction. This calculation is responsive to the power level and the detected signal size of the preceding scan.

Abstract: In order to decode from electrical signals derived by a photodetector which responds to the light returned from the relatively less reflective (black) bars of the code and relatively more reflective (white) bars (also known as spaces), these signals must be digitized into a digital data signal where the black and white bars are represented by opposite logic levels, (for example logic high voltage levels representing the black bars, and logic low voltage levels representing the white bars). The high logic levels are pulses which are separated in time by the low logic levels. A cascade of amplifiers is used to amplify the bar code signal from the photo detector. An amplifier having a logarithmic signal compression characteristic is included in the cascade, preferably after an amplifier which serves to differentiate the signal. The amplified signal is applied to a digitizer including a comparator which is sensitive only to the leading edge.

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 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: 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 bar code hand held scanning terminal which combines a data input device, a display and a scanning engine in a single portable unit. This unit is compact and may be employed in, for example, a scanning terminal which is attached to the back of a hand of an operator. Alternatively, the unit may be employed in a gun-type hand held scanning terminal. The combination has a display which is pivotally connected to the hand held scanning terminal such that the display may be in an open position or in a closed position. A light sensor is used to detect the opening or closing of the display portion of the hand held scanning terminal and maybe used to selectively deactivate the scanning beam when the display is open. The scanning device may be used to read bar code labels for inventory or warehousing, in medical prescription distribution, etc.