The United States of America As Represented by the Administrator of the

The United States of America As Represented by the Administrator

Other

The United States of America As Represented by the United States

Neillen Technologies, Corp.

Leonard L Kleinberg

An impedance-generating device that provides a resistance and a reactance that are non-linear functions of a signal over a wide impedance range (VariablE Non-Linear Impedance Circuit Electronics, 'VENICE'). An electronic component that has a gain characteristic with a unity gain frequency that is directly proportional to that signal can be configured to generate such an impedance. Such an electronic component configured to provide a negative effective resistance and a variable non-linear reactance can be used to implement a high frequency harmonic generator. This generator can provide high order harmonics which can be used in high frequency communications systems. The electronic component can also be configured to provide only a voltage-variable non-linear reactance which can be used to implement a reactive mixer to frequency shift a high frequency signal to an intermediate frequency signal, from mixing the high frequency signal with a local oscillator signal. This mixer provides a gain, at the intermediate frequency, that is the unity gain frequency of the electronic component divided by the intermediate frequency. Two stages of such mixers can be used in a homodyne circuit to generate the intermediate frequency signal without the use of off-chip bandpass filters. Also, an amplification to the intermediate frequency signal generated by the mixing can be used to implement a RF amplifier from the further modulation of this intermediate frequency signal on the local oscillator signal. These impedance-generating devices can thus implement high performance electronic circuits for communications applications.

Method and apparatus for generating non-linear variable impedance

An oscillating signal generator for generating an oscillating signal having a variable oscillation frequency that can be near the unity gain frequency of the gain devices within the oscillating signal generator (Generation of High-Frequency Oscillating Signal Techniques, 'GHOST'). Two gain stages, each with a respective effective resistance R.sub.eff, an emitter load capacitance C.sub.E, and a respective gain device having a unity gain frequency .omega..sub.T, are cascaded and configured to provide a respective gain with a phase at substantially 180.degree.. In that case, the oscillation frequency, of the oscillating signal generated by the oscillating signal generator of the present invention, .omega.=�.omega..sub.T /(R.sub.eff C.sub.E)!.sup.1/2. A feedback with a feedback gain is provided between the output to the input of the cascade of the two gain stages. The feedback gain is designed such that a product of the feedback gain and the gain through the cascade of the two gain stages is substantially one. The oscillation frequency of the oscillating signal generated by the oscillator can be varied by a corresponding variation to .omega..sub.T and/or R.sub.eff. Alternatively, the oscillation frequency can be substantially fixed at a predetermined resonance frequency determined by a frequency determining network operatively connected to the cascade of the two gain stages. The oscillating signal generator of the present invention which can generate sine waves can be implemented with circuit elements that are easily fabricated on-chip within a monolithic integrated circuit. In addition, because oscillation frequencies near the unity gain frequency of the gain devices can be achieved, higher frequencies for a given power dissipation or lower power dissipation for a given frequency can be obtained.

Oscillator having two cascaded gain stages with feedback operating near

A method and apparatus for increasing the bandwidth of an operational amplifier and including a capacitor being connected across the inverting and non-inverting inputs of the operational amplifier and further including a feedback circuit connected from the output to one of the inputs, the inverting input, and wherein the value of the capacitance is selected such that the time constant of an RC network including the capacitance and the feedback circuit impedance is proportional to the inverse of the product of the closed loop gain and a factor .beta. which equates the absolute value of the gain at two different frequencies.

Wideband gain stable amplifier

High input impedance amplifiers are provided which reduce the input impedance solely to a capacitive reactance, or, in a somewhat more complex design, provides an extremely high essentially infinite, capacitive reactance. In one embodiment, where the input impedance is reduced in essence, to solely a capacitive reactance, an operational amplifier in a follower configuration is driven at its non-inverting input and a resistor with a predetermined magnitude is connected between the inverting and non-inverting inputs. A second embodiment eliminates the capacitance from the input by adding a second stage to the first embodiment. The second stage is a second operational amplifier in a non-inverting gain-stage configuration where the output of the first follower stage drives the non-inverting input of the second stage and the output of the second stage is fed back to the non-inverting input of the first stage through a capacitor of a predetermined magnitude. These amplifiers, while generally useful, are very useful as sensor buffer amplifiers that may eliminate significant sources of error.

High input impedance amplifier

A reflection oscillator is provided which employs an active device operated in its roll-off region and two resonant circuits. For an oscillator employing a bipolar transistor, the emitter is connected to a series resonant capacitor-crystal network and the base is connected to an L-C tank circuit with the transistor being operated in the roll-off region of its gain versus frequency curve. This will provide a very high frequency of operation with a relatively inexpensive, low frequency, active device. These oscillators are easily tuned, stable, and require little d.c. power.

Reflection oscillators employing series resonant crystals'

A simple and inexpensive crystal oscillator is provided which employs negative voltage gain, single pole response amplifiers. The amplifiers may include such configurations as gate inverters, operational amplifiers and conventional bipolar transistor amplifiers, all of which operate at a frequency which is on the roll-off portion of their gain versus frequency curve. Several amplifier feedback circuit variations are employed to set desired bias levels and to allow the oscillator to operate at the crystal's fundamental frequency or at an overtone of the fundamental frequency. The oscillator is made less expensive than comparable oscillators by employing relatively low frequency amplifiers and operating them at roll-off, at frequencies beyond which they are customarily used. Simplicity is provided because operation at roll-off eliminates components ordinarily required in similar circuits to provide sufficient phase-shift in the feedback circuitry for oscillation to occur.

Crystal oscillators using negative voltage gain, single pole response

A temperature responsive transmitter is provided in which frequency varies linearly with temperature. The transmitter includes two identically biased transistors connected in parallel. A capacitor, which reflects into the common bases to generate negative resistance effectively in parallel with the capacitor, is connected to the common emitters. A crystal is effectively in parallel with the capacitor and the negative resistance. Oscillations occur if the magnitude of the absolute value of the negative resistance is less than the positive resistive impedance of the capacitor and the inductance of the crystal. The crystal has a large linear temperature coefficient and a resonant frequency which is substantially less than the gain-bandwidth product of the transistors to ensure that the crystal primarily determines the frequency of oscillation. A high-Q tank circuit having an inductor and a capacitor is connected to the common collectors to increase the collector current flow which in turn enhances the radiation of the oscillator frequency by the inductor.

Temperature responsive transmitter

A high frequency oscillator is provided by connecting two amplifier circuits in parallel where each amplifier circuit provides the other amplifier circuit with the conditions necessary for oscillation. The inherent noise present in both amplifier circuits causes the quiescent current, and in turn, the generated frequency, to change. The changes in quiescent current cause the transconductance and the load impedance of each amplifier circuit to vary, and this in turn results in opposing changes in the input susceptance of each amplifier circuit. Because the changes in input susceptance oppose each other, the changes in quiescent current also oppose each other. The net result is that frequency stability is enhanced.

Low phase noise oscillator using two parallel connected amplifiers

A predetermined and variable synthesized capacitance which may be incorporated into the resonant portion of an electronic oscillator for the purpose of tuning the oscillator comprises a programmable operational amplifier circuit. The operational amplifier circuit has its output connected to its inverting input, in a 'follower' configuration, by a network which is low impedance at the operational frequency of the circuit. The output of the operational amplifier is also connected to the non-inverting input by a capacitor. The non-inverting input appears as a synthesized capacitance which may be varied with a variation in gain-bandwidth product of the operational amplifier circuit. The gain-bandwidth product may, in turn, be varied with a variation in input set current with a digital to analog converter whose output is varied with a command word. The output impedance of the circuit may also be varied by varying the output set current. This circuit may provide very small changes in oscillator frequency with relatively large control voltages unaffected by noise.

Programmable electronic synthesized capacitance

An oscillator circuit for sensing and indicating temperature by changing oscillator frequency with temperature comprises a programmable operational amplifier which is operated on the roll-off portion of its gain versus frequency curve and has its output directly connected to the inverting input to place the amplifier in a follower configuration. Its output is also connected to the non-inverting input by a capacitor with a crystal or other tuned circuit also being connected to the non-inverting input. A resistor is connected to the program input of the amplifier to produce a given set current at a given temperature, the set current varying with temperature. As the set current changes, the gain-bandwidth of the amplifier changes and, in turn, the reflected capacitance across the crystal changes, thereby providing the desired change in oscillator frequency by pulling the crystal. There is no requirement that a crystal employed with this circuit display either a linear frequency change with temperature or a substantial frequency change with temperature.

Temperature sensitive oscillator

A high frequency oscillator circuit is provided using a low cost junction type field effect transistor (T.sub.1) with a tuned circuit connected to its gate. The frequency of operation is determined by the tuned circuit and the capacitance reflected from the source to the gate. The transistor is matched to the frequency of operation so that this frequency falls within the roll-off portion of the transistor's transconductance verses frequency curve, preferably somewhat above the 3 db point in frequency. Phase shifting necessary to sustain oscillation occurs due to the operation of the transistor in the roll-off portion of the curve and the addition of a phase shifting network (R.sub.1, C.sub.1) at the source. The resulting oscillator is small, stable, linear and inexpensive.

JFET Reflection oscillator

An active R bandpass filter network (10) is formed by four operational amplifier stages interconnected by discrete resistances. One pair of stages (12, 14) synthesizes an equivalent input impedance of an inductance (L.sub.eq) in parallel with a discrete resistance (R.sub.0) while the second pair of stages (16, 18) synthesizes an equivalent input impedance of a capacitance (C.sub.eq) serially coupled to another discrete resistance (R.sub.i) coupled in parallel with the first two stages. The equivalent input impedances aggregately define a tuned resonant bandpass filter in the roll-off regions of the operational amplifiers.

Reactanceless synthesized impedance bandpass amplifier

A bandpass amplifier employing a field effect transistor amplifier first stage (10) with a resistive load (R.sub.2) either a.c. or directly coupled to the non-inverting input of an operational amplifier second stage (20) which is loaded in a Wien Bridge configuration. The bandpass amplifier may be operated with a signal injected into the gate terminal (G) of the field effect transistor and the signal output taken from the output terminal of the operational amplifier. The operational amplifier stage appears as an inductive reactance, capacitive reactance and negative resistance at the non-inverting input of the operational amplifier, all of which appear in parallel with the resistive load (R.sub.2) of the field effect transistor.

Low noise tuned amplifier

A non-inverting, direct current amplifier stage is cascaded into an integrator stage to form a two stage tuned network (10) having a single input junction common to both stages. The network provides independent adjustment of center frequency, bandwidth and voltage gain. The insertion of a positive feedback loop between the stages provides a very narrow bandwidth network (10'). The addition of back-to-back zener diodes between the common input node and ground converts the network into an oscillator (10').

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Greenbelt, MD, United States of America

Leonard L Kleinberg