Showing papers on "Comparator applications published in 1970"

Search circuit for frequency synthesizer

Abstract: In an indirect digital frequency synthesizer comprising a voltage-controlled oscillator, a feedback loop connected from the oscillator output to its phase control input via a frequency divider, phase detector and low-pass filter, a reference frequency pulse source connected as a second input to the phase detector, and a digital comparator network for comparing the frequency of the feedback and reference pulses and generating output pulses when the feedback and reference pulses are not interlaced, a search circuit responsive to the frequency comparator output pulses for providing an error correction signal to the oscillator, whereby the oscillator is coarse tuned to within a frequency allowing the phase detector to accomplish phase lock of the feedback pulse train with the reference pulse train. For bidirectional tuning, two outputs are taken from the comparator, pulses at one output indicating the feedback frequency is too low and pulses at the other output indicating the feedback frequency is too high, and the search circuit comprises a capacitor having two pulse-controlled constant current sources, one responsive to pulses at one of the comparator outputs for charging the capacitor in a stepwise manner and the other responsive to pulses at the second comparator output for providing stepwise discharging of the capacitor. For unidirectional tuning, only one pulse output is taken from the comparator, and the search circuit comprises a capacitor having a pulse-controlled constant current source operative in response to comparator output pulses to stepwise charge the capacitor, with a dump circuit being provided to discharge the capacitor upon its charging to a predetermined maximum voltage level.

High-speed sample and hold signal level comparator

Abstract: A sample and hold comparator fabricated with emitter coupled logic using only one transistor-type, resistors, and interconnects and including a differential comparator and logic circuit for comparing an input signal VIN with a reference signal VREF in response to a short duration sample and hold pulse VS/H to produce a digital ONE or ZERO output signal depending upon whether the compared input signal is above or below the reference signal. The differential comparator and logic circuit being further responsive to a regenerative feedback signal produced by a differential amplifier in response to the output signal for latching or holding the state of the sample and hold comparator at the comparison state so that it is not further responsive to variations in the input signal VIN until after a reset pulse VRESET is received by it for clearing the sample and hold comparator circuitry.

High voltage functional comparator

Abstract: A comparator circuit has an hysteresis relationship between its two-level output signal and the input signal. As a result, the level of the output signal is substantially independent of noise on the input signal. By changing the value of a resistor the amount of hysteresis in the circuit is changed.

Temperature stable integrated oscillator

Abstract: A temperature stable integrated oscillator has a control loop including a flip-flop, a series resistor-capacitor timing circuit, reference voltage means and a comparator. The comparator compares the reference voltages to the voltage swing across the capacitor to actuate the flip-flop and thereby provide the oscillator output frequency. Temperature stability is provided by making both the voltage swing across the flip-flop and the reference voltage proportional to the difference between the power supply voltage and the base emitter drop of associated integrated transistors.

Midvalue signal selector

Abstract: A midvalue signal selector contains a channel for each of the signals to be compared. Each signal is applied to its respective channel through a comparator which produces a high- or low-level signal depending upon the comparative instantaneous values of the input signal and a feedback signal developed in that channel. Each channel contains a logic voter connected to receive the outputs of all comparators. The logic voter actuates a bipolar weighting switch in accordance with the high or low value of the majority of the signals applied to that logic voter. The output of the weighting switch in each channel is applied to a combination filter and operational amplifier which produces the output and feedback signals for that channel. The hysteresis inherent in a comparator, together with the filter circuit associated with the corresponding operational amplifier, produces an oscillatory signal at the output of the operational amplifier. The comparator receiving the midvalue signal produces a rectangular wave having a duty cycle dependent upon the magnitude of the midvalue signal. The output signal from the corresponding operational amplifier includes a DC component dependent upon the amount that this duty cycle deviates from 50 percent. The comparators of the remaining channels produce steady output signals so that the corresponding logic voters respond only to the midvalue signal.

Application of operational amplifiers to magnetic measurements

Abstract: The method of voltage integration using expensive stabilized high-gain and low-drift amplifiers has been previously described. Many low-price general-purpose amplifiers are now available, and their performance as voltage integrators (fluxmeters) is reported. The fluxmeter is intended for general use in factory test rooms where measurements consist of a single flux change over a few seconds unlike recording hysteresigraphs, where integration may be over several minutes, and where output voltage drift problems may arise. These electronic fluxmeters offer advantages over the conventional moving coil fluxmeter in that zero return is very fast and that they are particularly suited to pass-fail testing when used in conjunction with a reference voltage source and a voltage comparator. Both a reference source and a comparator can be constructed using similar types of operational amplifiers.

Signal comparator system

Abstract: A digitally controlled frequency generator is provided having a selectively variable output frequency with crystal controlled accuracy and stability. Should the desired output frequency drift, however, a phase comparator detects the drift and compares the phase thereof with a provided reference signal. The resultant error signal is then fed into the frequency generator to shift the frequency back to its original value. In addition, should it be desired to change the output frequency of the frequency generator, a new program is applied to a variable program counter which produces an electronic response representative of the new program. This response is sensed by both the phase comparator and an acquisition circuit, the acquisition circuit providing signals to the phase comparator to achieve a "lock-in" of the system at the new desired frequency.

Sawtooth generator with a ramp-bias voltage comparator

Abstract: In a sawtooth generator the voltage ramp across a condenser is compared with a bias voltage source. The ramp and bias voltages are applied, respectively, to the two input terminals of a bistable comparator. When the two voltages are equal the comparator output voltage changes state suddenly to operate a first switch to discharge the condenser, and second switch to close a positive feedback circuit from the output to the input of the comparator to insure the reliable switching action. The result is a linear ramp repeated at regular intervals free of the vagaries of noise voltages in the system.

Phase-lock-stabilized system for generating carrier frequencies usable in multiplex communication

Abstract: A voltage-responsive carrier-frequency oscillator, with a limited range of adjustability designed to compensate for frequency drifts, works through a frequency divider into a phase comparator also receiving a relatively low base frequency harmonically related to the desired carrier frequency. The output of the phase comparator is fed back to the oscillator to maintain a predetermined phase relationship between the two low frequencies. The phase comparator includes a pair of differentiation circuits, deriving respective pulse trains from these low frequencies, and a flip-flop alternately set and reset by interleaved pulses from the two trains; the integrated output wave of the flip-flop constitutes the feedback voltage controlling the output frequency of the oscillator.

Pulse code modulation feedback encoders

Abstract: A pulse code modulation encoder having two comparators, one receiving analogue signals to be encoded via a unity gain amplifier and the other arranged to receive signals after they have been amplified by a fixed amount. If the analogue signal is above a predetermined value it is fed to the one comparator and if below the predetermined value it is fed to the other comparator. The predetermined value is the voltage represented by the first amplitude digit of the P.C.M. code and dependent upon whether the analogue signal is above or below the predetermined value then AND gates in the comparator outputs are either inhibited or enabled.

Audio to digital converter

Abstract: An audio-to-digital converter having a comparator means for comparing an audio input with a feedback signal. The feedback is coupled to the comparator through a feedback control device so that a constant comparison occurs.

Integrated level detector circuit with gating arrangement to inhibit transient output signals in response to energization of the circuit

Abstract: A level detector circuit suitable for embodiment in integrated circuit form includes a comparator circuit and reference voltage generator energized by a common voltage source. The level detector monitors the voltage of an incoming signal by utilizing the comparator circuit to compare this signal with the generated reference voltage. The reference voltage is generated in response to a current source energizing a breakdown diode. The output of the comparator is temporarily inhibited during the transient initial energization of the comparator and the reference voltage generator to prevent false alarm signals. The output is inhibited by an inhibit gate circuit arrangement which is energized by a driving circuit operative prior to breakdown of the breakdown diode. An additional feature of the invention is a signal inversion scheme energized by the reference voltage generator which permits voltages of opposite polarity to that of the reference and energization voltages to be compared with the magnitude of the reference voltage by the comparator.