Abstract: Two filter sections having different frequency responses are interconnected via selectively enabled switches, formed on the same integrated circuit (IC) as the filter sections, between a signal input terminal and a signal output terminal. The selectively enabled switches can be used to: (a) selectively connect the two filter sections in cascade between the signal input and output terminals to produce a bandpass filter; or (b) selectively connect the two filter sections in parallel to produce a notch filter, or (c) couple only one of the two filter sections between the signal input and output terminals; or (d) provide a short circuit between the signal input and output terminals. In a preferred embodiment the filter sections are switched capacitor filters. The filter system of the invention is highly suited for use in an engine knock signal processor integrated circuit.

Abstract: A transconductance amplifier suitable for the input stage of a comparator with the capability of amplifying input signal with common mode voltage components in a range including the entirety of its operating voltage. Operation at one voltage extreme is accomplished by use of a long tailed pair connection of a pair of bulk modulated FETs with gates at the input terminals of the amplifier. Operation at the other voltage extreme is accomplished by the use of a pair of FETs in a source follower mode to drive common gate transistors of opposite polarity, the gates of the FETs also being connected to the input terminals of the amplifier. A common high impedance load for the comparator is connected to current mirrors of the drains of both pairs of FETs in the amplifier. The circuit may be implemented with bipolar transistors and additional amplification provided. Methods of comparing voltages are also disclosed.

Abstract: An amplifier system embodying the invention includes an input stage comprising one or more differential amplifiers having a high degree of common mode rejection. The inputs of the differential amplifiers of the input stage are AC coupled to different signal input terminals which are adapted to receive small information signals riding on large common mode signals. The AC coupling blocks any dc level associated with the input signals from affecting the amplifier system and the high degree of common mode rejection maintains the gain of the amplifiers relatively constant over a wide range of common mode signals. The outputs of the differential amplifiers of the input stage are connected in common to an output node to sum their output signals and to reduce random noise associated with the input signals and the input stage. The output node of the input stage is AC coupled to the input of a second stage whose output is in turn AC coupled to a third output stage to reduce the effect of amplifier offsets.

Abstract: Signals applied to the gate of an enhancement-mode field effect transistor by resistive coupling, via a dc-blocking capacitor, are self-biased. The self biasing is carried out by detecting the signal amplitude and applying a portion of the direct voltage from this detection to the gate of the field effect transistor through the coupling resistor.

Abstract: A differential current amplifier includes a differential input transistor pair having respective first and second unity gain current mirror amplifiers (CMA) connected in their respective output circuits. The output terminal of the CMA connected in the output circuit of the first transistor of the differential pair is connected to the input terminal of the second transistor of the differential pair. The output terminal of the CMA connected in the output circuit of the second transistor is connected to the input terminal of the first transistor. The current feedback to the input terminals of the differential pair conditions them to be responsive to input signal currents. An amplifier output current can be derived from an additional current output from one of the first and second CMA's, the additional CMA output having a gain of A relative to the unity gain output.

Abstract: A bandgap reference voltage generating circuit develops a predetermined reference potential between first and second terminals. A pair of transistors are operated at different emitter current densities to develop a difference between their base-emitter potentials. That difference is applied across a first resistance and is increased and applied across a second resistance. The reference potential comprises the sum of at least the scaled-up potential and the conduction potential of a semiconductor junction. A regulating transistor completes a degenerative feedback connection and controls the current flowing between the first and second terminals responsive to the reference potential departing from the predetermined value. A regenerative feedback connection responds to the current in the regulating transistor to decrease the potential across the second resistance when the controlled current increases.

Abstract: A position sensing and display means for use on a weighing scale includes two stationary spaced conductive plates to which out-of-phase oscillations are supplied. A movable conductive plate has a position between the two stationary plates dependent on the weight of an object being measured. The amplitude of the oscillations capacitively coupled to the movable conductive plate is displayed as an indication of the weight of the object.

Abstract: A plural-stage amplifier circuit having improved common-mode input voltage range includes first and second transistors connected to form a first long-tailed pair, third and fourth transistors connected to form a second long-tailed pair in cascade connection after the first long-tailed pair, a first current supply providing tail current to the first long-tailed pair, a second current supply having a plurality of outputs providing collector currents to the first long-tailed pair, and a third current supply providing tail current to the second long-tailed pair. The output currents of the first, second and third current supplies are controlled in proportion to a control current which permits the voltage across the third current supply to be controlled such that the first and second transistors do not saturate at input voltages approaching the supply voltage.

Abstract: A system for use in battery powered alarm equipment for self-testing such battery for a low voltage and a high series resistance condition, and particularly for use in systems which utilize a starting capacitor in combination with the battery to provide a high starting current to the alarm annunciator. For periodic battery tests, a resistor is selectively connected across the battery and the resulting voltage drop at the battery terminals is compared to a reference voltage supply. Energy stored in the starting capacitor is prevented from discharging through the battery test circuit by a transistor switch operated in the inverse mode for disconnecting the starting capacitor from one of the battery terminals during such battery tests so that substantially no current is supplied from the starting capacitor through the test circuit.

Abstract: First and second transistors are connected in long-tailed-pair amplifier configuration, with interconnected emitter electrodes connected to a constant current generator that supplies the tail current. Input signals applied to the base electrodes of these transistors are pre-distorted by diodes connecting the base electrodes of the first and second transistors to a common node point. These diodes are provided forward bias currents from constant current generators, so they float with regard to common-mode components of the input signals and do not impair the common-mode signal rejection of the long-tailed-pair amplifier configuration.

Abstract: A three-terminal current amplifier has a current gain substantially independent of the forward current gains of its component transistors. It employs a first transistor with collector-to-base feedback regulating its collector current flow to equal applied input current and a second transistor having a base emitter circuit in parallel with that of the first transistor. Output current from the collector electrode of the second transistor consequently is proportional to the input current. Means are provided for maintaining the collector potentials of the first and second transistors substantially equal to help maintain a fixed relationship between the output and input current amplitudes.