Showing papers on "Comparator applications published in 1976"

Analog-digital converter with variable threshold levels

Abstract: An analog-digital converter comprises a comparator to which signals to be converted are applied, and a threshold circuit coupled with the comparator in order to control the threshold level of the comparator, so that the signals applied to the comparator are converted into binary signals based upon a predetermined threshold level. The threshold level corresponding to the output of the threshold circuit is compensated in accordance with the variations in the levels of the signals applied to the comparator. The threshold level of the comparator is changed to a compensated level when the result, calculated from the average level of the signals approximately corresponding to a predetermined area in a field of the object and that of the signals approximately corresponding to plural areas which are in the vicinity of the predetermined area, is different from that of the preceding frame.

Comparator circuit for a C-2C A/D and D/A converter

Abstract: A comparator circuit for comparing two voltage levels in a C-2C A/D and D/A converter, comprising four cross-coupled active devices (FETs) in a latch arrangement whereby an offset voltage is used to compensate for imbalances in the comparator. The comparator includes a first FET having its gate electrode connected to the output of the D/A converter, and a second FET having its gate electrode connected to an analog input voltage. The first and second FETs each have one of their electrodes connected to a common voltage source. A third and a fourth FET have one of their electrodes connected respectively to the other electrode of the first and second FETs at first and second common nodes, respectively. The output of the comparator is provided at one of such first and second common nodes. The first and second nodes are also respectively connected to the gate electrodes of the fourth and third FETs in a cross-coupled arrangement. The other electrode of both the third and fourth FETs are connected to a common phase voltage source. An offset voltage is generated at the input to either of the gate electrodes of the first and second FETs to set the comparator at a balance point and thereby compensate for the differences in the threshold voltages and current carrying capabilities of the four FETs. Also, the comparator has relatively high input impedance, gain and bandwidth.

High accuracy MOS comparator

Abstract: The voltages to be compared are applied to a passive MOS capacitor differencing circuit for producing a voltage difference signal, which then is amplified by a high-gain non-precision FET amplifier, the output of which is passed through a low output impedance FET buffer amplifier to a FET latching circuit. Capacitive coupling is used for enabling the amplifiers to be independently biased and to eliminate D.C. offsets. The operating cycle of the comparator has two periods. During an initial set-up or preconditioning period the amplifiers are self-biased by appropriate switching actions which cause each of the amplifiers to be set at a desired operating point that is maintained when its respective bias switching connection subsequently is opened. The bias switch openings in the respective amplifier and latching stages are timed to occur in a chosen sequence which causes the switching transients to be absorbed. At the end of the preconditioning period, the comparator is set up for operation in the comparison period during which the input signals are compared.

Cmos comparator circuit and method of manufacture

Abstract: A chopper stabilized comparator which compares two low level DC signals, and converts these signals to an AC signal which is amplified by AC amplifiers. The AC amplifier output is proportional to the difference between the two DC signals. The circuit has the advantage that it does not have any DC offset terms, for example, it does not drift with temperature. The comparator is implemented in CMOS technology wherein the actual physical layout of the circuit is chosen such that changes in mask orientation during the fabrication process have no effect upon the proper operation of the circuit.

Dynamic threshold tone detector

Abstract: The presence of a tone in a received signal is detected by passing the signal through a bandpass filter tuned to the frequency of interest. The output from the filter is peak detected and applied both to the first input of a comparator and to a unique variable threshold circuit which, in turn, is coupled to the remaining comparator input. The threshold circuit tracks the peak detected level of the bandpass filter output such that the comparator is activated between its logic states, representing the detect or undetect condition, with a minimum of delay time.

High-gain differential input comparator with emitter feedback input hysteresis

Abstract: A high-voltage gain, high-current gain comparator circuit including a pair of input transistors, a constant current source, an unbalanced pair of multiple emitter active load transistors and a signal amplifier with emitter feedback to one of the active load transistors for achieving input signal hysteresis characteristics. The circuit has differential inputs, a single-ended output, inherent noise immunity and is particularly well suited for fabrication as an integrated circuit in a chip of semiconductor material.

Variable thresholding circuit for converting an analog signal to a binary signal

Abstract: A variable thresholding circuit for converting an analog signal to a binary signal comprises a comparator to which signals to be converted are applied and a threshold circuit coupled with the comparator in order to provide the threshold level of the comparator, so that the signals applied to the comparator are converted into binary signals in accordance with the threshold level. The threshold level corresponding to the output of the threshold circuit is compensated in accordance with the variations of the levels of the signals applied to the comparator. The threshold level of the comparator is changed to a compensated level when the result calculated from the threshold level and the signals applied to the comparator is smaller than a predetermined value, whereas the threshold level of the comparator is not changed to the compensated one when the result calculated from the threshold level and the signals applied to the comparator is larger than that and the compensation is repeated until the calculated result becomes smaller than the predetermined value.

Circuit arrangement for evaluating signals, particularly output signals of optical measuring devices

Abstract: The circuit arrangement includes a measuring device having an output circuit connected to one input of a comparator, and including a voltage divider whose tap is connected to the other input of the comparator. A storage capacitor is connected to the tap of the voltage divider and to such other input of the comparator and provides a reference voltage bearing a fixed relation to, but always lower than, the signal voltage of the measuring device in the quiescent state of the arrangement. A bias voltage may be applied to the tap of the voltage divider. When the measuring device responds to a test object, the voltages at the comparator inputs are so switched that the reference voltage is held above the signal voltage until the measuring device returns to the quiescent state. In the quiescent state, the signal voltage exceeds the reference voltage and the comparator, changing back to the zero state, restores the initial condition of the two voltages. A switching arrangement is provided which, when the reference voltage falls below a predetermined minimum value, and if the arrangement has not switched to the operating state, provides a corresponding logic signal.

A current comparator bridge for power measurement

Abstract: A current comparator technique for the measurement of sinusoidal ac power at 60 Hz is described. The reference power is that generated by applying the voltage across a 10-kΩ resistor. The voltage itself is measured by comparing it directly to a dc reference with an ac/dc rms voltage comparator. The current is compared with the current comparator to the current in the resistor for the in-phase or active power component, and to the current in a capacitor for the quadrature or reactive power component. Six-digit resolution is provided for both components. The bridge can be operated over a voltage range from 50 to 150 V and a current range from 0.01 to 1 A at any power factor. An auxiliary current transformer provides extension of the current range to 10 A. Comparison measurements with a Drysdale wattmeter used as an ac/dc power transfer standard indicates agreement at unity power factor to within 25 ppm.

Wide range current flow fault detector

Abstract: A wide range current flow fault detector comprising a current sensor and a selective interrogator are disclosed. Current flow, or the lack thereof, between a power supply (e.g., capacitor bank) and a load (e.g, the hammer coils of a line printer) is sensed by a current sensor connected to detect the voltages at spaced points along a selected length of the supply conductor connecting the power supply to the load. A differential amplifier forming a part of the current sensor produces an output voltage related to the voltage difference between the selected points. The output voltage of the differential amplifier is compared, in a comparator, with a preset voltage. Any time the output voltage of the differential amplifier is above the preset voltage, the output of the comparator changes from a first state (e.g., low) to a second state (e.g., high). At all other times, the output of the comparator remains in the first state. Thus, the output state of the comparator denotes the presence or absence of current flow through the supply conductor adequate to cause the output of the differential amplifier to rise above the preset level. The interrogator selectively interrogates the output of the comparator to determine if: (1) a current adequate to raise the differential amplifier output above the preset level exists when such a current should be flowing through the supply conductor; and (2) zero current or a current inadequate to raise the differential amplifier output above the preset level exists when zero or very little current should be flowing through the supply conductor.

Transistor oscillator circuit using thermal feedback for oscillation

Abstract: Disclosed is a monolithic oscillator circuit which relies upon the thermal characteristics of the semiconductor chip for oscillation. The circuit includes, in one embodiment, first and second transistors with similar output characteristics coupled to the input of a comparator element, and a third transistor coupled to the output of the comparator. The first and second transistors are unbalanced and the third transistor is placed close to only one of these transistors so that any heat generated will primarily affect the output of only the adjacent transistor. Thus, when a current flows from the comparator through the third transistor, the generated heat will decrease the potential across the first and second transistors until they are balanced, and the current through the comparator will shut off. The current remains off until the transistor cools off and an unbalanced condition is again achieved. The circuit may be integrated in a chip of small size and so is particularly suited for inclusion in light emitting diode packages.

Voltage to frequency conversion - involves using quartz oscillator operational amplifier and logic circuit to overcome voltage and capacitive variation effects

Abstract: A voltage to frequency conversion circuit uses an integrating operational amplifier, comparators, a quartz oscillator and a logic circuit to overcome the effect on frequency of integrating capacitor and voltage variations. The convertor input (A) is connected via two switches (10, 11) to input resistors of the amplifier (1), whose output is connected to inputs of three comparators (2, 3, 4). The comparator outputs are connected to a logic circuit (5), which is also supplied by the oscillator (6), and which controls the input switches (10, 11) and further amplifier (1) input switches (12, 13). One comparator (4) has an input grounded via a resistor (7) and connected via a resistor (8) to its output which is also the convertor output (D). The output may be provided by a digital counter in another arrangement.

Digital phase comparator

Abstract: A high gain digital phase comparator which in digital phase lock loop systems can give a thousand-fold reduction in ripple and close-in noise sideband amplitudes. The comparator is of the sample-and-hold type but the normal ramp reference waveform is replaced by a trapezoidal waveform with a very steep rising or falling slope generated by a trapezoidal waveform generator. This slope is sampled by a sampling circuit coupled to said generator and its steepness gives the increased gain of the phase comparator leading to the reduced noise and ripple. Additional logic and switching circuits are added to make the comparator operate only during a rising edge of the trapezoidal waveform.

Phase comparator and process for the operation thereof

Abstract: A phase comparator has at least two signal comparison inputs and at least one resistance line and one or more voltage amplitude comparators. A first comparator input of each voltage amplitude comparator is connected to the resistance line. One end of the resistance line is connected by way of a first dc voltage blocking means to the first signal comparison input and the second signal comparison input is connected by way of an inverter and a second dc voltage blocking means to the other end of the resistance line. In one mode of operation the one end of the resistance line is connected to a fixed voltage and the other end is connected to an impressed current source, and the second comparator inputs of all the voltage amplitude comparators are connected to a fixed reference voltage which is equal to the arithmetic mean of the two voltages present at the ends of the resistance line and produced by the current source and the voltage source. In this mode of operation each signal comparison input is fed with one of two input signals which are to be compared and the output signal of the phase comparator is provided in parallel from all of the comparator outputs. In another mode of operation, one end of the resistance line is connected to a fixed voltage and the other end is connected to an impressed current source. The second comparator input of all the voltage amplitude comparators are connected to a fixed reference voltage which is equal to the arithmetic mean of the two voltages present at the ends of the resistance line and produced by the fixed voltage and the impressed current source. The two ends of a second resistance line are connected to a fixed voltage and a further resistor has one end connected to a tap of the second resistance line and another end connected to a fixed voltage. In this mode of operation each signal comparison input is fed, in each case, with one of the two input signals which are to be compared and the output signal of the phase comparator is obtained at the tap of the second resistance line.

Current regulating circuit for magnetic deflection systems

Abstract: The current in the deflection coil of a video display system is converted into a DC voltage and applied to a peak detector. Peak values of the DC voltages as stored by the peak detector are amplified and then compared with a reference voltage at the input of a comparator amplifier. The comparator amplifier provides an output as a base drive to a regulating transistor that has an emitter-collector junction in series with the deflection coil and an unregulated source of DC power.

Variable on-and off-time relaxation oscillator

Abstract: A relaxation oscillator comprising three cascaded operational voltage comparators is described. The on-time of the inventive circuit is established in accordance with a variable input element to the first operational comparator. The off-time is established by an RC network in the input circuit of the second operational comparator. The first and second operational comparators are interconnected so that the turning on or off of the second operational comparator affects the first operational comparator to cause it to also turn on or off.

Programmable voltage sensing circuit

Abstract: A simple, reliable and sensitive electrical circuit for detecting when a first input exceeds a second input and vice versa and producing corresponding signals at first and second outputs comprising first and second operational amplifiers each having its negative input connected to its output and its positive input serving as a circuit input to function as a voltage follower, first and second comparator circuits with the positive input to the first comparator being directly connected to the output of the first amplifier and the negative input to the output of the second amplifier via voltage dividing resistors so that the output thereof goes to zero when the output of the first amplifier drops below the divided output of the second and with the second comparator similarly connected so that the output thereof goes to zero when the output of the second amplifier drops below the divided output of the first amplifier. The circuit finds particular utility in a system for detecting yarn or thread breakage or for counting.

Circuit for calibrating instruments

Abstract: A circuit permitting an operator to accurately calibrate an instrument to indicate when a variable analog quantity being measured is zero. The analog signal is connected to the input of an operational amplifier which operates in stable mode for large analog inputs and operates in oscillation mode for very small analog inputs. The output of the operational amplifier is compared to zero and when the analog input is greater than zero, the comparator output is a logic zero. When the analog input is less than zero and not in the immediate vicinity of zero, the comparator output is a logic one. When the analog input is very small and less than zero, the operational amplifier operates in oscillation mode as the circuitry connected thereto causes it to oscillate with the duty cycle of the negative portion of the oscillation decreasing as the analog input comes closer to zero. Accordingly, the output of the comparator also oscillates. The comparator output connects to a sign driver of a typical seven segment display and the sign indication provided thereby grows dimmer as the analog input approaches zero from the negative direction.

Linear A-D converter using successive subtraction - uses amplifier simultaneously as comparator to simplify cct

Abstract: The linear analog/digital converter uses successive subtraction of simple construction without comparators. The amplifiers in the section coders, realised as inverting operational amplifiers (Vj) are designed as polarity separating amplifiers with two summation resistors in the input circuit, one resistor (R1) between the inverting input of the operational amplifier and the input of the section coder, and the other one (R2) from the inverting input through a change-over switch (Sj) which is normally connected to reference voltage and can be switched to earth. The feedback loop for signals of a polarity to be doubly amplified contains a decoupling diode (D1) and a resistor (R4) of twice the value of that between the operational amplifier and input. The other feedback loop has a decoupling diode (D2) and a limiter (Di) limiting the digital output voltage to the logice level of the digital switching circuit in use. The digital output connected to the control input of the changeover switch lies between the decoupling diode and the voltage limiter. This has the effect that the double-gain amplifier is used simultaneously as a comparator.

Electronic voltage regulator for electric motors - comparator generates square wave with frequency and mark space varied to adjust average value

Abstract: An electronic voltage regulator for electric motor drives uses digital switching output stage to minimise power boss. The constant voltage source delivers an output dependent upon the reference voltage setting. A comparator stage compares the reference with the actual voltage supplied to the motor and the difference signal controls the power stage. The comparator output is digited, with zero output level if the difference is positive and a one output level of the difference is negative. The power stage output is therefore in the form of a square wave. The regulation is achieved by generating an average of the signal that is varied by frequency and mark/space ratio changes. To protect the output stage against overload a cut-out stage (14) is provided.

Control point driver circuit

Abstract: A control point driver circuit for use in a telephone exchange for energizing and deenergizing a control element such as a control relay in response to set and reset input pulses. The control point driver circuit comprises a transformer having a centertapped primary forming set, reset, and common inputs for receiving the set and reset input pulses and a secondary coupled to a constant control voltage. The control point driver circuit also includes a comparator having a first input coupled to the transformer secondary, an output coupled to the control relay to be energized and de-energized and a second input coupled to the comparator output for receiving first and second reference voltages which are related in magnitude to the constant control voltage to maintain the comparator in the set state or reset state indefinitely until a reset or set input pulse is received. A received input pulse causes an induced voltage within the transformer secondary which augments the control voltage to change the relation in magnitude between the reference voltages and the control voltage to cause the comparator to change states in response to the received set and reset input pulses. When the comparator is in the set state, the control relay is energized and when the comparator is in the reset state, the control relay is de-energized.

The synchronized astable multivibrator bridge as a voltage-to-time convertor, a voltage comparator and an error detector

Abstract: The synchronized astable multivibrator bridge is used as a new, sensitive, linear, temperature stable, reliable voltage-to-time converter, voltage comparator, zero crossing detector, error detector of an on-off servomechanism (for example as a contactless thermostat with thyristors), voltage differential transducer, measuring device with digital counter for voltage or corresponding nonelectric quantities (temperature pH etc.), convenient even for remote operations. The discrimination capability of the error detector or comparator, limited by the bridge jitter, is about 500 mu V. If the comparator is used with the preamplifier, its discrimination capability improves to about 0.4 mu V. The bridge as a comparator, employed with a Pt-Pt/Rh thermocouple, for temperature measurement and regulation within the range of about +or-50 degrees C around 1000 degrees C has a discrimination capability of about 0.2 degrees C.