Abstract: Common mode error correction for differential amplifiers involves accurately measuring both the input and output of an amplifier using a low-leakage measurement path, and calculating common-mode gain. Two measurements are made at each node by appying two different common-mode voltages. Subtracting one set of measurements from the other eliminates voltage offset errors, and leaves a common-mode error term for gain calculation. The common-mode gain factor is stored, and thereafter, common mode error may be subtracted from measurements made by the differential amplifier.

Abstract: According to the present invention, a power amplifier with a plurality of power transistors has detection circuitry corresponding to each power transistor which detects the output power of the power transistors and allows this output power to be monitored and modified if desired. The detection circuitry generates a voltage output signal indicative of the rise and fall times achieved by the power transistor. The voltage output signal of the detection circuitry may be monitored by connecting the voltage output signal to a measuring device, such as an oscilloscope of built-in-test-equipment (BITE). Additionally, the voltage output signal of the detection circuitry may be modified by tuning input matching circuitry and/or output matching circuitry accordingly.

Abstract: An amplifier calibration apparatus for use in an audio device which processes an audio signal. The audio device includes a manual volume control for manually altering the gain of the signal. An amplifier which may include a digital potentiometer serves to alter the gain of the audio signal in response to a control signal. The amplifier calibration apparatus, which serves to automatically calibrate the amplifier, includes a controller; a waveform generator, which generates a known waveform, and a comparator circuit. The known waveform is fed into the amplifier and the resulting amplifier output is fed into the comparator circuit. The comparator compares a constant signal to the amplifier output resulting in a comparison output indicative of any difference between the two signals. The comparison signal is operably connected to the controller such that the controller can calibrate the full scale point of the amplifier.

Abstract: A test system for measuring the characteristics of an active circuit employs a pulsed bias technique for periodically biasing the input control port of the active circuit into the active region of operation. Biasing is achieved with a bias voltage that is periodically pulsed ON and OFF. An RF source is pulse modulated ON and OFF synchronously with the pulsed bias voltage and applied to the input control port of the active circuit. The pulsed RF occupies a portion of the time interval encompassed by the pulsed bias voltage. These voltages are combined and applied to the input port of the active circuit which operates only during the presence of the pulsed bias voltage and which is OFF during the absence of the pulsed bias voltage. A DC supply is utilized to bias the output port. The amplified RF power is then measured at the output port of the circuit, after the RF power has been separated from the DC bias by a non-reciprocal device.

Abstract: A device for testing an amplifier. A plurality of PN modulators are provided corresponding to a plurality of oscillators at stages preceding or following them, or fluctuation is given to division ratios at the oscillators. Since each of n carriers combined by a combiner contains phase fluctuation, the possibility that the peaks will overlap each other or that the carriers having opposite phases will negate each other is very low. The peak power in signals supplied to the amplifier to be tested is unlikely to vary, enabling accurate evaluation or testing.

Abstract: A Cartesian amplifier in which an input signal is pre-processed and split into two quadrature components. Both quadrature components are passed, in parallel, through an error amplifier (4), after which they are re-combined and up-converted to RF. The output of the amplifier is used to provide a feedback signal. This feedback is downconverted from RF to baseband and resolved into two quadrature components which are fed to the respective inputs of the error amplifier (4). Periodically the pre-processor (3) is switched into a calibration mode in which test signals are applied to the amplifier instead of the input signal. At these times the signal strength of the output of the power amplifier is measured and used to provide pre-distortion factors in the signal preprocessor (3) to improve amplifier linearity.

Abstract: In a logarithmic amplifier circuit including a plurality of cascaded differential amplifiers, a plurality of blocks of logarithmic full-wave rectifiers are provided, each producing output currents having logarithmic full-wave rectification characteristics in respect to voltages of their input signals. Each logarithmic full-wave rectifier is formed by a plurality of squaring full-wave rectifiers each producing an intermediate current having squaring full-wave characteristics. A current adder is provided for each or a group of the squaring full-wave rectifiers to add up the intermediate currents thereof and produce an output current. A common adder is provided for adding the output currents from all logarithmic full-wave rectifiers to produce a current output signal.

Abstract: In a receiver comprising a receiver filter (12) with a frequency attenuation band and a pilot oscillator (25) for generating a pilot oscillation signal with a pilot frequency in the frequency attenuation band, a coupler (26) couples the pilot oscillation signal and a filtered receiver signal of the receiver filter to form a coupled signal. A low noise amplifier (13) amplifies the coupled signal into an amplified signal which comprises an amplified receiver signal component derived from the filtered receiver signal and an amplified pilot oscillation signal component derived from the pilot oscillation signal. A branching filter (27) branches the amplified signal into the amplified receiver signal component and the amplified pilot oscillation signal. A pilot signal component detector unit (28) detects the amplified pilot oscillation signal component to produce a direct pilot signal.

Abstract: A detector for detecting changes in the output level of an amplifier included in, for example, a mobile communication signal. A first detecting circuit produces a detected voltage having linearity against low output levels of the amplifier. A second detecting circuit produces a detected voltage which is linear against high output levels of the amplifier. The detected voltages from the first and second detecting circuits are mixed by a mixer in a predetermined ratio. Even when the output level of the amplifier changes over a broad dynamic range, the detector detects the changes with accuracy.

Abstract: A vertical amplifier system for a multitrace oscilloscope including a first and a second variable gain amplifiers each connected to each channel of a multitrace oscilloscope. First, a first reference voltage is fed to the two variable gain amplifiers at the same time. The polarity of output of the second variable gain amplifier is inverted, and the inverted output is added to the output of the first variable gain amplifier by an adder. The added result is detected by a resistor. A CPU automatically controls a gain of at least one of the variable gain amplifiers while receiving the added result so that the added result becomes zero. Second, a second reference voltage (a ground level voltage, for example) is applied to both variable gain amplifiers, and an offset of at least one of the variable gain amplifiers is adjusted so that the added result detected by the resistor becomes zero. The input-output characteristics of both variable gain amplifiers are equalized with high accuracy.

Abstract: A virtual sensing system includes a sensing network that is external to a standard cell for sensing a reference current in the standard cell and for generating a scaled current without breaking the reference current path and without inserting any sensing device in series with the reference current. The reference current can be used, for example, for duplication and/or scaling.

Abstract: An amplifier level-setting apparatus is provided for obtaining the maximum power output and highest efficiency allowable for a predetermined level of distortion. According to the invention, a training signal is applied to the input of the amplifier prior to the desired signal. The training signal level is increased while the output distortion is measured. When the output distortion level reaches a predetermined limit, the corresponding training signal input level is saved. The input signal level is then adjusted to this saved level value, thereby resulting in the maximum amplifier output level possible that is still within the distortion limit.

Abstract: The automatic gain control method adapted to maintain the output level equal of the variable gain amplifier to a required value, includes a preliminary calibration phase for establishing a relationship representing the variations in the amplifier gain control signal as a function of variations in the input signal level with a constant output level equal to the required value or as a function of variations in the output signal level for a constant input signal level.

Abstract: Improvements in the circuits and techniques for read, write and erase of EEprom memory enable nonvolatile multi-state memory to operate with enhanced performance over an extended period of time. In the improved circuits for normal read, and read between write or erase for verification, the reading is made relative to a set of threshold levels as provided by a corresponding set of reference cells which closely track and make adjustment for the variations presented by the memory cells. In one embodiment, each Flash sector of memory cells has its own reference cells for reading the cells in the sector, and a set of reference cells also exists for the whole memory chip acting as a master reference. In another embodiment, the reading is made relative to a set of threshold levels simultaneously by means of a one-to-many current mirror circuit.

Abstract: A load connection state detector circuit for use in a stereophonic system comprises: a check mode setting circuit for generating a check mode signal to perform checking; an offset generator circuit for generating an offset voltage from an input-stage amplification section according to the check mode signal; a first current detector circuit for detecting a current flowing to a first load according to the offset voltage; a second current detector circuit for detecting a current to a second load according to the offset voltage; and a difference-current detector circuit for detecting whether or not a difference current between output currents of the first and second current detector circuits falls within a predetermined range.

Abstract: A multichannel amplifier employs field-effect transistors to vary the gain of operational amplifiers in each respective channel. Gain matching of the respective channels is obtained by providing each channel with a respective DC bias voltage which compensates for differences in pinch-off voltage of the field-effect transistors. The invention permits the use of inexpensive, unmatched JFETs in the amplifier. Close gain tracking achieves very accurate stereo imaging in an audio system.

Abstract: The present invention relates to a tuning aid system for manually operated vacuum tube type RF power amplifiers. The tuning sequence is simplified by providing a visual indication of a region where the plate current and grid current of the vacuum tube indicate that the amplifier is properly tuned. In particular, the plate current and grid current of the vacuum tube are monitored and the readings thereof are coordinated by means of a visual display which indicates when the amplifier is properly tuned. In an aspect of the invention, the visual display also includes directions for modifying the level of the plate current and/or grid current on either side of the tuned region.

Abstract: An MOS current mirror includes a floating node onto which and from which electrons may be transported by control signals and electrical semiconductor structures in order to adapt the current mirror to supply a desired output current when a particular input calibration current is present.

Abstract: Automatic Level Control (ALC) circuit having a directional coupler, for branching an output of an amplifier, and a detector, for detecting the branched output, is disclosed. When saturation of the amplifier is measured, coupling by the directional coupler is decreased and the input signal to the detector can be kept below a predetermined value.

Abstract: A test apparatus and method is disclosed for determining the absolute noise figure of an optical amplifier. The apparatus comprises an optical receiver and functions to measure the output power of a test noise source, such as a lamp or LED. A plot of input power versus output power yields a linear relationship, with a y-intercept at the test apparatus (first) noise floor (N.sub.0). An optical amplifier to be tested is then inserted in the signal path between the noise source and the receiver. A new plot is generated and a second system noise floor value is determined (N.sub.1). The difference between the two noise floor values (N.sub.1 -N.sub.0) is then defined as the amplifier absolute noise figure (N.sub.A). The inventive technique is equally applicable to semiconductor and fiber optical amplifiers.

Abstract: A circuit for sensing the output distortion of amplifier stages of the type which has a first input which receives a voltage signal to be amplified, a second input connected to a feedback network and an output which generates an amplified output signal. The circuit comprises at least one comparator, which receives in input a first signal which is correlated to the voltage signal and a second signal which is correlated to the output signal of the amplifier stage, and is enabled so as to generate a distortion signal in output when the second signal exceeds the first one in terms of absolute value, i.e. in the presence of distortion.

Abstract: A detection circuit including a first and second sensing circuits detects the presence of load current provided by a utilization circuit to which the detection circuit is coupled to provide an output current that is proportional to the load current. A fraction of the load current that is sourced from the utilization circuit flows through the first sensing circuit the latter of which then provides an output current proportional to the fractional load current. Similarly, a fraction of load current that is sunk by the utilization circuit flows through the second sensing means which provides an output current proportional to the fractional load current.

Abstract: Frequency characteristic setting circuitry for an amplifier generates frequency band data groups using a plurality of characteristic pattern data groups stored in a memory. Each of the frequency band data groups is made by making each item of data of a characteristic pattern data group retrieved from among a plurality of characteristic pattern data groups stored in the memory correspond to each frequency in a designated frequency band. The data groups generated for a plurality of frequency bands are combined together and the equalizing characteristic of the amplifier is controlled according to a characteristic pattern data group obtained by the combination.

Abstract: An adjustable slew rate amplifier in the input stage of an amplifier circuit helps reduce off-channel frequency splatter. In instances where test sequences are input to an amplifier circuit that are used to measure maximum permissible input levels to the amplifier, inclusion of a low slew rate amplifier in the input loop further prevents the production of off-channel frequency splatter caused even by the input test sequence. The adjustable slew rate amplifier is run at full slew rate, providing full-bandwidth amplification, during periods of normal circuit operation.

Abstract: A novel CATV signal distribution system includes a head end, a plurality of taps, lines including a coaxial line connecting the head end with the taps, and at least one signal amplifier in the coaxial line, the amplifier for producing output signals within a prescribed range of operating parameters. The novel system includes a local status monitor operatively connected to and in close proximity with one or more of the amplifiers in the system. Each status monitor is adjusted to produce a status signal that is visually, aurally or otherwise detectable by service personnel in the vicinity of the amplifier when the amplifier malfunctions. A novel local status monitor circuit for use in the novel system is also disclosed.

Abstract: A control system for an audio amplifier including a control module interconnected by an edge connector to an amplifier to monitor status signals and the audio input and output signals from the amplifier. The control module passes serial data to an interface which interconnects the plurality of control modules and amplifiers to a single host computer. The host computer receives data from the interface and transmits instructions to the interface for routing to the specific amplifier control module to control the amplifier's gain along with other audio functions and a remote power supply. The control module can be set to run in a stand alone mode to regulate the amplifiers thermal dynamic response to the audio signals and prevent thermal clipping.

Abstract: A test circuit for use in testing amplifiers in order to check that they are functioning properly at operational power levels. The test circuit includes switching mechanisms which configure the amplifier in feedback mode in order to cause the amplifier to oscillate and a circuitry for measuring the power output of the amplifier during oscillation in order to thereby check that it is properly operational. The circuit may also include a load acting as a fixed attenuator for dissipating the power output of the amplifier and a bandpass filter for selecting an appropriate frequency of oscillation for the amplifier. The circuit may also include a control loop for regulating the amount of feedback and controlling the output power level.

Abstract: A method and apparatus for enabling the continuous monitoring of the operational state of circuit components includes a scheme for generating a plurality of voltage signals representing neutral-to-line voltages of the system and adding to each of those signals a second signal, each second signal being identical. This addition is done vectorially to yield a modified signal. A representation of the modified signal as acted upon by the circuit to be monitored is compared with a representation of the neutral-to-line voltage signal to yield an output signal representative of the operational state of the circuit components.

Abstract: Apparatus used for local simulation of a metallic pair of 22 Gauge conductors, such as comprising a telephone line, 6.5 miles in length at 70 degrees Fahrenheit consisting of a resistance network. This apparatus is useful for fault identification of telephone line amplifiers, allowing for local activation when used in conjunction with milliampere test meters, in lieu of a technician's required travel to a minimum of 6 miles to perform the same task. This apparatus is useful in that it allows for function testing of typical line amplifiers at the source of the metallic pair.

Abstract: The invention relates to an amplifier arrangement with load independent saturation detection, including an input stage (7) having a first and a second input terminal (5, 6), an output stage (8) coupled to the input stage (7) and having at least one output transistor (T1, T2), and an output terminal (4) connected to the first input terminal (5) via a coupling network (R1, R2, C). In order to obtain a detection signal when the at least one output transistor (T1, T2) becomes saturated, there is provided a detection device, (16) coupled to the input stage (7) to detect, during operation, an amplitude difference between a signal (V.sub.i) to be amplified, which signal is applied to the second input terminal (6), and a portion (V.sub.t) of the signal (V.sub.o) appearing on the output terminal (4), which portion is applied to the first input terminal (5) via the coupling network (R1, R2, C).

Abstract: A method for calibrating measurement or analysis systems that is externally traceable, simple, and repeatable, which is particularly amenable to computer control, and a unique programmable phase-gain amplifier which is especially suited for use in the calibration method, are disclosed. Alternatively, a programmable sample clock delay technique is disclosed to provide phase calibration. The method employs an externally traceable digital voltmeter to measure the magnitude of the signal being applied to an input channel of the measurement system; and obtains a digital representation of the output of the channel. When the input magnitude does not match the output magnitude, the programmable phase-gain amplifier gain is adjusted. These adjustments are made for each range of each channel.

Abstract: A protective earmuff which transmits normal sound levels and clips higher amplitude sound levels by causing an amplifier to go into saturation when the input signal is greater than a preset amount. The sound is received by a microphone, amplified and transmitted to the ear of the user by a speaker. The output of volume level is controllable independently of the clipping level. Also disclosed is a circuit allowing user control of both the clipping level and the volume level independently.

Abstract: A monitor signal injection system for a feedforward cancellation amplifier having at least one stage in which monitor signals having a constant relatively large amplitude are injected into, for example, a main amplifier. The monitor signals are used to measure the status of all individual components of the amplifier and are useful for fault detection and isolation. In addition, the monitor signals are cancelled in the output to a very low level and as a result, on-line monitoring can be performed without significant radiation of power from a load antenna.

Abstract: The present invention provides a precision variable gain current-to-voltage amplifier which has a test mode of operation wherein the gain is independent of the gain of the amplifier when operated in the normal amplification mode. The invention enables a test signal, preferably a test voltage, to be injected into the amplifier circuit to test the functioning of the op amp and thus the amplifier. Because the gain of the amplifier in the test mode is independent of the gain of the amplifier when in the normal mode, a simple and easy method of checking the functioning of the op amp is provided which does not require knowing the gain of the amplifier and then selecting the proper test input to use.

Abstract: An improved alternating current amplifier employs capacitive feedback to balance the intrinsic input capacitance, and a multiplier circuit responsive to a digital control signal coupled in the feedback path to vary the effective capacitance of the capacitive feedback. Thus, the frequency response of the amplifier may be adjusted and set digitally, such as under computer control, obviating the need to make manual adjustments to improve amplifier performance.

Abstract: In an amplifier stage comprising a pair of input current sources, connected in series between a pair of reference potential lines, a pair of output transistors connected between the pair of reference potential lines and defining an intermediate output terminal of the amplifier, a driving circuit comprising active elements and interposed between the input current source and the output transistors, and at least one saturation control circuit comprising at least one control transistor connected with its base to the driving circuit and with its collector and emitter between the output of the amplifier stage and the intermediate point between the input current sources, to detect distortion due to clipping, at least one distribution detection transistor is provided, connected to the control transistor so as to detect the current flowing through the latter, which current is related to the imbalance of the input current sources and therefore to the distortion generated in the stage.

Abstract: A method of proving safe operation of a complex electronic circuit, and apparatus for carrying out the method, in which a proving signal having known characteristics is superimposed on an input to the circuit and the output is searched for said characteristics. An example involves the use of a microprocessor arranged to evaluate a fast Fourier transform algorithm on the coded carrier signal of a railway automatic train protection system or of railway a.c. track circuit arrangement.

Abstract: A device and process for programmatically generated and controlled in-circuit pin tests and gross functionality tests of operational amplifiers. The tests provide basic functionality verification of amplifier functions independent of other circuitry on the printed circuit board of which the operational amplifier is a component.

Abstract: In an intermediate frequency amplification circuit comprising first through n-th differential amplifiers which are connected in cascade to one another with the first amplifier supplied with a circuit input signal and which successively produce amplifier output signals with an n-th amplifier output signal produced as a circuit output signal from the n-th amplifier, first through (n+1)-th rectification circuits are supplied with respective amplifier output signals with the circuit input signal given to the first rectification circuit. Each rectification circuit comprises a differential unit comprising at least one pair of transistors which have different emitter areas from each other to rectify each amplifier output signal and to produce a collector current which is summed up by an adder circuit to be produced as a field strength signal. The rectification circuits may carry out either half-wave rectification or full-wave rectification.

Abstract: A plurality of amplifier channels, wherein each channel is automatically gain controlled by a gain control signal and wherein the gain of each channel is a known function of a plurality of constants of corresponding to each amplifier and of the gain control signal, can be calibrated by the following method. The method comprising the steps of measuring each output of each amplifier at a corresponding plurality of gain control values and at a corresponding input to each amplifier. The number of the plurality of the constants equals the number of the plurality of the gain control values. The method continues by computing the gain of each amplifier at the step of measuring. The constants corresponding to each amplifier are then computed according to the function and computed gain. A corresponding changed gain control signal is applied to each amplifier according to the function to set the corresponding gain of each amplifier to a corresponding predetermined calibrated value.

Abstract: An apparatus for field testing a feedforward amplifier includes a source of an RF signal and a source of an audio frequency signal. Both of these signals are applied to the feedforward amplifier under test. A failure in one of the active elements in the feedforward amplifier will increase the level of distortion and thus produce audio-frequency sidebands on the RF carrier at the output of the feedforward amplifier. These audio sidebands are detected in a double balanced mixer which also receives a phase-shifted RF test signal. The output of the double balanced mixer is representative of the level of amplifier distortion and thus of a failure in the feedforward amplifier.

Abstract: A logarithmic amplifier calibrator internal to an electronic instrument applies a swept frequency signal via a switch and a single pole resonator to a logarithmic amplifier to be calibrated. The logarithmic amplifier output is digitized and stored as a frequency response for the resonator. The switch is opened and the single pole resonator rings down through the logarithmic amplifier. The ringdown output of the logarithmic amplifier also is digitized and stored as a linear log response. A ripple error look-up table is generated from the linear log response. An approximate bandwidth for the resonator is determined from the frequency response and a ringdown time corresponding to the time the linear log response decreases from the maximum amplitude to a 3 dB down amplitude of the frequency response to determine the exact bandwidth for the resonator.

Abstract: Apparatus and method for performing low-frequency noise measurements on active devices such as operational amplifiers, instrumentation amplifiers and the like. A device under test is settled thermally in a short, controlled interval. The device under test is placed in a test fixture within a closed housing which shields against air flow. A substantial heat sink is urged against the device under test while a pre-heat circuit preheats the device for about 1-2 seconds by forcing it to consume a predetermined amount of energy. The voltage output of the device under test is supplied to a band-pass filter which includes a high-pass filter having a single dominant pole whose frequency may be varied. A control circuit smoothly moves that pole from a first, higher frequency of about 50 Hz to a second, lower frequency of about 0.1 Hz in an interval of only 3 seconds or so, rapidly settling the filter.

Abstract: A circuit for measuring the leakage current of an electrometer amplifier 10 determines the leakage currents at both amplifier input terminals simultaneously by a method that eliminates the effects of the amplifier offset voltage as well as of the offset voltages and leakage currents of the amplifiers (22 and 40) used in the measurement. With no amp. under test present in the circuit, measurements are made of the outputs of the two test-circuit amplifiers (22 and 40). This results in quantities that indicate the required compensation for the offset voltages and leakage currents of the test-circuit amplifiers. From then on, measurements are made of the amplifier output voltages with an amp. under test present and the leakage currents at both input terminals of said amplifier 10 under test can be inferred from these second measurements by using the information obtained from the first set of measurements.

Abstract: A method and system for enhancing the performance of feedforward amplifiers includes the provision of multiple sweep displays, one each for providing a display of a single performance characteristic of the amplifier. Various characteristics are monitored on an alternating and interleaved basis, and displayed during the intervals that they are monitored. The monitoring intervals are short enough so that each display appears to be continuous. The performance characteristics of the amplifier are thus observable on a real time basis, thereby facilitating adjustment of the amplifier to achieve optimum overall operation.

Abstract: A differential charge amplifier design for a hydrophone pre-amplifier inces a calibration circuit for in situ measurement of the hydrophone/pre-amplifier gain. The hydrophone signal is input to a pair of amplifier stages which form a balanced differential input charge amplifier. The signal from the input charge amplifier is amplified by a second pre-amplifier stage and then passed to a balanced output cable driver. The calibration circuit is enabled by an external signal to inject a calibration signal into the input charge amplifier front end.

Abstract: An intermediate frequency amplifier stage is disclosed, in which linearity of a signal strength detection output is improved. The intermediate frequency amplifier stage includes a plurality of intermediate frequency amplifiers, a plurality of double-wave rectifiers each coupled to the associated intermediate frequency amplifier and making full-wave rectification of the signal supplied from the associated intermediate frequency amplifier, and an adder circuit adding the rectification outputs of the respective double-wave rectifiers.

Abstract: A method of fault sensing for a power amplifier having direct coupled power stages with normally mutually exclusive current flow in which the alternating current output is simultaneously sensed and, when a fault is detected, is ANDed. A power reduction to the amplifier is initiated when the ANDed output exists for a selected period of time.

Abstract: A dead zone in the transfer function of a signal processing system, such as a VTR, is detected by impressing on the system a test signal that is formed within a predetermined interval from a sinusoidal waveform modulated by an envelope function that reduces to zero at a predetermined time. The existence of the dead zone is detected by observing whether the corresponding output signal of the signal processing system has a constant amplitude at times other than the time at which the envelope function is zero.

Abstract: Disclosed is a level detector in use with a differential amplifier circuit in an amplitude-limiting amplifying system for angle-modulation signal amplification. The differential amplifier circuit is made up of differentially paired transistors. The level detector contains first and second transistors which form a differential pair. In the first transistor, the base is connected to an interjunction of the emitters of the differentially paired transistors. A second transistor is connected at the emitter to the emitter of the first transistor. A current source is connected to the emitter interjunction of the first and second transistors. A bias circuit applies a predetermined bias potential to the base of the second transistor. An output signal containing the detected level information of the input signal is derived from the collector of the first or second transistor.