Showing papers on "Comparator applications published in 1980"

Pulse width modulation of printhead voltage

Abstract: An electronic thermal printer has a thermal printhead to which is applied a train of pulses which is pulse width modulated. A power switch connects and disconnects the printhead from a DC power source. The pulse train is integrated, scaled and applied as an input to a comparator circuit. The thermal printhead has a temperature sensing diode whose output is applied, as a reference voltage, to the other input of the comparator. During a print cycle, the output of the temperature sensing diode is cut off and the reference voltage is capacitively stored and held as the reference voltage. The output of the comparator circuit clears a latch circuit whose input is provided by a system clock and whose output is connected to control the power switch. The comparator provides an output when the integrated voltage reaches the reference voltage, clearing the latch. Since the latch is supplied with signals from the system clock, a constant frequency is maintained. However, the varying output from the comparator clearing the latch provides varying pulse widths. In this manner, pulse width modulation of the voltage input pulses to the thermal printhead is achieved.

Apparatus for reproducing disc record

Abstract: Apparatus for maintaining a constant linear velocity for a PCM disc record which includes a detector for optically detecting the PCM signal on the record and supplies the output to a differentiating circuit and a rectifier circuit with the output of the rectifier circuit supplied to a peak detector circuit which supplies its output to a level comparator that also receives a reference level from a reference source. A first phase comparator also receives the output of the rectifier circuit and controls a voltage controlled oscillator through a low pass filter and the output of the voltage controlled oscillator is supplied to the phase comparator. A divider receives the output of the voltage controlled oscillator and supplies a first input to a phase comparator which also receives an input from a reference frequency generator. The outputs of the level comparator and the phase comparator are supplied to the motor drive circuit which controls the drive motor for the disc record.

Digital phase comparator with improved sensitivity for small phase differences

Abstract: A digital phase comparator for essentially eliminating the dead zone in the phase correction means of a phase locked loop. The digital phase comparator is arranged to provide respective up and down output pulses to operate respective charge pumps. The up and down output pulses at all times are greater than a predetermined time duration no matter how small the phase difference between comparator input signals. A delay means is provided in the phase comparator logic, which delay means substantially determines such predetermined time duration. The minimum pulse duration of the up and down signals is selected to be at least of a duration sufficient to operate its respective charge pump, thereby overcoming the finite turn on time of the respective charge pump, no matter how small the phase error.

Temperature sensing circuit with high noise immunity

Abstract: A refrigerator includes a compressor, a condenser, an evaporator, an evaporator fan and a temperature sensing circuit which includes a thermistor located to sense the average temperature of the cabinet air and a potentiometer manually adjustable to a desired temperature set point. The temperature sensing circuit also includes a first comparator stage which indicates whether the average temperature of the cabinet air is above or below a first value, the first comparator having little or no hysteresis in its response so that small changes in temperature can be detected. A second comparator stage indicates whether a signal at its input is greater or less than a second value, the second comparator stage having substantial hysteresis in its response to provide high noise immunity. An integrator is interposed between the first comparator stage and the second comparator stage to further enhance noise suppression.

Zero-crossing comparators with threshold validation

Abstract: In carrier and timing recovery systems for high performance data modems it is essential to employ threshold comparators and to be able to determine accurately zero-crossing instants. The circuit of the invention comprises a comparator with feedback which produces a positive transition of the comparator output in response to the negative zero-crossing transition of the input signal on condition that the previous half-cycle of the input signal has exceeded the positive reference threshold. In a practical arrangement two comparators (C1, C2) provided together with a pair of bistable storage elements (D1,D2) which produces a narrow pulse in response to the negative zero-crossing transition of an input signal (IPS) provided that the input signal (IPS) has exceeded the positive reference threshold (+VT) applied to the second comparator (C2).

Liquid absence detector

Abstract: A system is provided for detecting the absence of liquid in a liquid chamber. A signal is transmitted through a liquid chamber and a signal is provided in response to the amplitude of the received signal. A receiving transducer receives an AC signal which is amplified and fed to a DC control circuit. A reference voltage is provided to one input of a comparator and the output of the DC control circuit is fed to the other input of the comparator. The comparator output provides the liquid absence signal if the difference between the reference voltage and the DC control circuit output voltage is less than a predetermined value.

Low voltage, low power RC oscillator circuit

Abstract: A resistor-capacitor oscillator circuit (10) is provided and includes a voltage comparator circuit (12). A capacitor (20) is connected to an input terminal (14) of the voltage comparator circuit (12). A resistor divider network (30) is coupled to an input terminal (16) of the voltage comparator circuit (12) for generating a reference voltage. A delay circuit (50, 52) is coupled to an output terminal (42) of the voltage comparator circuit (12). A discharge device (54) is coupled to the delay circuit (50, 52) and to the capacitor (20) for discharging the capacitor (20). A switching device (40) is coupled to the output (42) of the voltage comparator circuit (12) and to the resistor divider network (30) for controlling the application of the reference voltage to voltage comparator circuit (12).

Apparatus for use in testing an internal combustion engine ignition system

Abstract: An apparatus for testing an i.c.e. ignition system of the kind including an ignition coil and a semi-conductor switch means controlling current interruption in the coil primary, includes a voltage comparator connected to compare the voltage across the switch means with a predetermined voltage. The comparator output starts a monostable timer circuit, the output of which is gated with the output of the comparator to produce an output signal only if the voltage across the switch means falls below the predetermined voltage within a predetermined time duration.

Voltage comparator hysteresis control circuit

Abstract: A voltage comparator includes a hysteresis control circuit which utilizes a level threshold device. The comparator has a first input coupled to an unknown voltage and a second input coupled to a threshold voltage. The hysteresis control circuit includes means for generating a hysteresis current which is caused to flow through a hysteresis resistor coupled to the second input when the threshold voltage exceeds the threshold of the level threshold device and the unknown voltage is greater than the voltage on the second input of the comparator.

Digital phase comparator circuit

Abstract: of the Disclosure A digital phase comparator circuit comprises a digital phase comparator having output terminals and a circuit connected to the output terminals of the phase comparator and arranged to remove erroneous pulse output signals simultaneously appearing at the output terminals due to propagation delay times of logic gates incorporated in the phase comparator.

Device for measuring the level of a liquid

Abstract: A device for measuring the level of a liquid, comprising a high temperature coefficient sensor immersed in the liquid, a detection circuit connected to the sensor for delivering a voltage indicative of the level of liquid, a memory circuit to which said voltage is applied, a saw-tooth signal generator circuit and, a comparator. The output signals of the memory circuit and of the saw-tooth signal circuit are coupled to input terminals of the comparator, and a display galvanometer is connected to the output of said comparator.

Electronic ignition-coil control device for an internal combustion engine

Abstract: The primary winding of an ignition coil is placed in series with the collor of a switching transistor. In order to protect the transistor against overvoltages, the collector is also connected to a level comparator and the base receives a two-state control signal which is synchronous with the rotation of the engine. One input of the comparator is connected through a divider network to the collector of the transistor and the outer input is connected to a fixed direct-current voltage source. Provision is also made for an error amplifier connected to the output of the comparator, and for a summing circuit which is connected to the control input of the transistor and receives the control signal.

High power and/or high voltage switching operational amplifier

Abstract: There is disclosed a high power and/or high voltage switching operational amplifier arrangement having a comparator with a first input for a low frequency AC signal. The output of the comparator is connected with the data input of a bistable element. The bistable element is triggered by a clock pulse signal with a rate substantially higher than the frequency of the AC input signal. An amplifying stage arranged between both poles of a high power and/or high voltage source is composed of a pair of alternately operating switch means, each arranged between a respective pole of the voltage source and a common amplifier stage output. Each of the switch means is coupled by a control input to at least one of the outputs of the bistable element. A low pass filter network coupled to the amplifier stage output forms the output stage of the operational amplifier arrangement. Means for providing feedback are arranged between the filter network and a second input of the comparator.

Differential current detector in cable television trunk amplifier station

Abstract: A voltage comparator compares the DC current in active elements of a trunk amplifier with a variable reference voltage for detecting when to switch to a bypass mode. Its output is normally low for passing a current through it, an LED, and relay coils when the amplifier operates satisfactorily. Circuitry for establishing an allowable amount of decrease in DC current in a current sensing resistor R5, prior to switching the comparator for de-energizing the relay coils, comprises a first transistor Q4 that continuously conducts collector current through a load resistor, a second transistor Q2 that is only responsive to a low output voltage of the comparator for passing a prescribed current through the load resistor for decreasing the first transistor Q4 collector voltage a prescribed amount, and circuitry including voltage dividers for coupling a greater percentage of the change in Q4 collector voltage to the positive input of the comparator than to the negative input thereof which also senses the level of the DC current.

CMOS Analog to digital converter with selectable voltage follower buffering

Abstract: An analog to digital converter is fabricated using CMOS construction and uses a successive approximation register to develop the bits in a digital word. A digital to analog converter converts the digital word to analog voltages which are compared with the analog input. The comparator is coupled to the register so as to determine its word bit sequence. The digital words most significant bit is set first in accordance with whether the analog input is greater or less than half of the reference voltage. Then the next most significant bit is evaluated and this process is continued until the least significant bit is evaluated at which time the conversion is complete. In the CMOS circuit, a switched comparator is employed and it draws a capacitor charging current in its operation. Accordingly, it is useful to buffer the comparator input. Two buffers are employed, one p-type and one n-type. They have common inputs and outputs that are selected as a function of the most significant bit in the digital word. The selected output is coupled to the comparator so that the comparator does not load the analog signal input.

Transistor circuit having two comparator levels

Abstract: A comparator receives an input voltage as well as one of two comparator levels and compares them to selectively produce one of two outputs having different values. A comparator level generator is connected to the comparator for selectively applying one of the two comparator levels to the comparator under the control of a controlling means. The controlling means is connected to both of the comparator level generator and the comparator for controlling the comparator level generator so as to change the comparator level in response to the new state of the comparator.

Phase locked loop for use with discontinuous input signals

Abstract: A PLL circuit which comprises a phase comparator, a voltage-controlled oscillator whose oscillation frequency is controlled by an output from the phase comparator, a flip-flop circuit adapted to be set by an input signal, and a counter circuit responsive to an output condition of the flip-flop circuit to count an output from the voltage-controlled oscillator. The flip-flop circuit is adapted to be reset by an output from the counter circuit, and the phase comparator is adapted to receive an output from the flip-flop circuit and the output from the voltage-controlled oscillator.

Vehicle electrical system diagnostic unit - reduces noise by operating independently of supply, and contains window comparator, logic and display

Abstract: An arrangement for testing electrical systems in vehicles with a current measurement probe requires fewer connections than conventional systems and eliminates the previously necessary connection to the electrical supply. Ignition transients are thus reduced and the operating reliability improved, in partic. for digital and computer-controlled systems. A voltage proportional to the measurement current is used to determine the condition of the electrical system. The voltage is displayed on an oscillograph or recorder showing the peak and/or average value. The voltage is also input to a window comparator with variable upper and lower limits. The comparator output is fed to evaluation logic which drives an analogue or digital display and controls the comparator.

Evaluation circuit for electrical signals

Abstract: Signals from a coil producing pulses in response to flux variations produced by a rotary member driven by an engine crankshaft are applied in push-pull through series resistors to the inverting and non-inverting inputs of a comparator. A variable voltage divider for the input signals is provided by a pair of complementary transistors respectively connecting the comparator inputs to opposite poles of a fixed voltage supply. The comparator pulses charge a capacitor through a transistor, the capacitor being periodically discharged through a resistor, once per crankshaft revolution. An increase of capacitor voltage beyond a very small amount progressively lowers the resistances provided by the transistors connected to the comparator inputs, acting on one of them simply through a transistor and on the other through a transistor and a current mirror circuit. In order to compensate for the temperature dependent leakage current of the transistor driven by the comparator output in order to charge the capacitor, a second current mirror is provided that prevents charging of the capacitor during the blocked-condition of the transistor in question. A supplementary voltage divider is connected through isolating series resistors to set the d.c. level of the comparator inputs when the transistors connected to these inputs are non-conducting.

Parity checking circuit for continuous voltage signals - used for process or circuit function monitoring, including multichannel comparator with digital output

Abstract: The circuit has an input channel for each voltage signal and a multi-channel comparator (VG1, VG2) coupled in series with each input channel comparing the respective voltage signal with at least one further voltage signal. Each comparator channel (VG1, VG2) provides a digital output with two possible values, with all the comparator channels (VG1, VG2) connected to a common circuit output (A) via a switch (R), such that an output signal, indicating correct functioning of all circuits etc. is only provided when the output signals form all the channels have a selected value outof the two possible values. Pref. each comparator channel (VG1, VG2) uses different circuit components and/or layout so that they have different responses to temp. variations, store electromagnetic fields etc.

A fast, latching comparator for 12 bit A/D applications

Abstract: High-speed, 12 bit accurate successive approximation A/D converters demand a comparator with both excellent input specifications and fast response time The author describes a voltage comparator with 50 ns response time to 1/2 LSB overdrive (12 mV) and 01 LSB (250 /spl mu/V) total input error Unique features of the circuit include a super-/spl beta/ input stage, a fast buried-zener level-shift, a fully differential output stage, a floating-zener biasing scheme, and a fast latch circuit which does not interfere with input accuracy The comparator is manufactured on a bipolar, double-implanted, thin epi, junction-isolated process

Circuit arrangement for consecutively monitoring operating conditions of direct current devices

Abstract: The circuit arrangement monitors operating conditions of consecutively sampled direct current devices. The operating conditions are represented by different potentials occurring at a sampling connector of each different direct current device. A selector unit has parallel signal inputs, each of which inputs is connected to a respective sampling point of a DC device. A comparator is coupled by a first input to a reference voltage source and by a second input to the output of the selector unit. An output of the comparator is connected to a shift register buffering the output signals of the comparator for one monitoring cycle. The selector unit and the shift register are commonly controlled for synchronous selecting operation and shifting, respectively. There is arranged a feedback network between the output of the shift register and the first input of the comparator for superposing a positive feedback signal on the reference voltage.

Signal multiplying amplifier system - has two operational amplifiers of very wide band type operating in parallel and with common signal input and output

Abstract: The amplifier system is intended for rapid, highly precise analog-digital conversion It comprises operational amplifiers with a Schottky diode bridge in their feedback branch Two operational amplifiers (OP1, OP2) of very wide band type are used, having a shared signal input (UE) and a shared signal output (UA) The first amplifier is of non-inverting mode, the second one being inverting at the same rate In the output and feedback branch of both operational amplifiers are incorporated Schottky diode bridges (B1, B2) A rapid comparator (K) is connected to the shared signal input, the comparator output being fed to a bridge current drive circuit (BT), controlling the Schottky diode bridges In this manner these bridges operate as an ON-OFF switch with external control for each output signal of the operational amplifiers

Diversity reception system for opposing fading - uses ring counter and comparator in logic system to control sequential aerial switching

Abstract: The diversity reception system for opposing fading uses a set of aerials connected to a switching system with a set of inputs corresponding to the number aerials connected to a multi-stable circuit which receives control pulses to operate a changeover from one aerial connection to another. This multi-stable device can be a ring counter, and the next aerial in the set is selected in turn, then the first aerial is again connected. The output of the receiver is connected with a stage which monitors the quality of the received signal. The voltage level of the intermediate frequency can be used as the reference value, also the signal to noise ratio or distortion can be used. An operational amplifier can be used as a comparator. A control unit connected to the ring counter receives pulses from a pulse generator and signals from the comparator. A memory supplies signals to the comparator and the whole forms a logical control system for the control unit.

ECL compatible integrated circuit A=D converter - has identical comparators coupled in groups to multiple-input AND=gates

Abstract: The analog/digital converter has identical comparators connected at one input to one of a series of equidistant reference voltages and at the other to a shared input signal rail. The number n is given by n = 2m - 1, whre m is the number of AND-gates each with 2m-1 inputs connected to the outputs of the comparators. Each AND-gate input is connected to only one comparator. Groups containing 2m-1 comparators are connected to the path comparator. The comparator with the lowest number in the first group assigned to the path gate has the number 2m-1 and there are 2m-1 comparators between each group.

Condition responsive inductance to frequency converter with temperature compensation

Abstract: A circuit arrangement for converting an inductance value into a specific frequency particularly for producing a pressure-dependent frequency fully compensated against variations in temperature for injection systems in internal combustion engines. The circuit arrangement comprises a comparator, the output of which is connected to a series circuit comprising at least one diode, a coil with variable inductance and a temperature-dependent resistor, all connected to a current supply line with the end of the coil opposite the comparator output coupled back to a first input of the comparator. The potential of the second input of the comparator can be affected by the output value of a voltage divider between the two current supply lines and a regenerative feedback line emanating from the output of the comparator. During the operation of the circuit arrangement, a pulse sequence is obtained, the frequency of which is determined by the inductance.

Digital stabiliser suitable for testing communication lines - converts into AC output voltage of constant amplitude and of same frequency using comparator

Abstract: The amplitude stabiliser has two or more m-stage counters receiving clock pulses from a clock generator. A comparator compares the contents of the counters with the contents of a third m-stage counter. The third counter counts pulses of 2n times the frequency. Each time the comparator's inputs are equal, a counter with n+1 stages moves on and has its output converted into analog form. The advantage lies in using purely digital means to stabilise an a.c. input.

Control circuit with two variable impedances - has two operational amplifiers controlling both impedances in dynamic companders

Abstract: The control circuit has its second variable impedance (13) located in the d.c. feedback path of a comparator that generates a control signal for the first impedance (21). At least one of the connections (22, 23) to the first impedance is connected to an input (29) of a transfer component (27). The control input (24) of the first impedance is connected to the output of the comparator (6) and to the output of the transfer component. The transfer value between the connections of the first impedance and the control input of the first impedance is unity. The comparator and the transfer component are differential amplifiers. The second impedance is connected between one input of the comparator and a first reference voltage. The value of the second impedance is, therefore, independent of the reference voltage applied to it. Field-effect transistors, diodes, or transistors may be used as the impedances.

Interval timer circuit.

Abstract: An interval timer circuit including a single comparator (12) having first (14) and second (16) inputs thereto and an output (18) therefrom. The circuit includes a series connected resistive and capacitive means (R1, R2, C1) having a control point (A) which is connected for varying the voltage of the second input (16) of the comparator. A first reference voltage is established by a first means (R3, R4) at the first input (14) of the comparator whereby its output (18) changes from a second state to a first state when an increasing voltage at the control point (A) exceeds the first reference voltage. A second means (R4, R5, CR2) establishes a second reference voltage at the first input (14) of the comparator in response to the first state at the output thereof. A third diode means (CR1) produces a decreasing voltage at the control point (A) in response to the first state and when the decreasing voltage at the control point (A) is less than the second reference voltage, the output (18) of the comparator (12) changes to its second state to repeat the process.

Recording system AC amplifier over-drive circuit - feeds end-stage operating voltage and reference control signal to comparator providing output to control display

Abstract: The overdriving display uses a control signal (UST) corresp. to the peak value of the amplifier output signal. This control signal (UST) is supplied to a comparator (7) for comparison with a reference control signal (URef) corresp. to the operating voltage of the amplifier end stage, with the display (9) controlled by the comparator output. Pref. the operating voltage (UB) for the amplifier end stage is supplied to the second input of the comparator via a voltage divider (8), with a division ratio varied in dependence on the operating voltage (UB). the voltage divider (8) may include a series circuit with a zener diode and a resistor. Both the comparator (7) and the amplifier may use operational amplifiers and the display (9) may comprise a LED.