An arrangement to provide feedback to amplifier systems incorporating an inductive laod. A low value error-sensing resistor is incorporated in conjunction with one or more transistors to provide a feedback correction signal to an amplifier which corrects for distortion caused by both the amplifier and the inductive load. A first embodiment providing a single-ended amplifier system incorporates an error-sensing resistor in series with a transistor, an inductive load and a bias resistor. A negative feedback error signal is provided to the amplifier from a point between the error-sensing resistor and the bias resistor. A second embodiment additionally includes a transformer to isolate the load. The third embodiment provides push-pull amplifier configurations. The third embodiment incorporates two complementary transistors to drive an inductive load. A pick-off arrangement including two capacitors and an error-sensing resistor provides negative feedback to the amplifier.
An amplifier comprising an emitter-coupled pair of transistors having inductive load impedances, with capacitive feedback elements tuned with the inductive loads and the capacitive input of the following stage to be resonant at the range of frequencies to be amplified. The reactive loads and feedback elements introduce less noise than with resistive components.
The tail current of a differential transistor pair (12 and 14) is controlled by a feed-back means (40) that couples the pair's tail node (16) to the control input of each transistor for controlling a biasing current through each transistor. The control input of each transistor further receives an input signal in addition to an output signal of the feed-back means. As a result, the circuit has a stable and accurate tail current, and in addition is suitable for a low-voltage supply or for high-current operation.
A clipper includes an amplifier having a non-inverting input node, an inverting input node, and an output node. A feedback transistor has its base connected to the amplifier output node and its collector connected to the non-inverting input node for providing unilaterally conductive degenerative current feedback between the output node and the non-inverting input node. A resistor is connected between the non-inverting input node and an input terminal for conducting a current supplied via the collector-to-emitter path of the feedback transistor which is proportional to the amplitude of an unclipped portion of the signal applied between the input terminal and the inverting input node. When a reference potential is applied to the inverting input node and an AC input signal varying about the reference potential is applied to the input terminal, the stage functions as a negative half-wave rectifier. When the reference potential is applied to the input terminal and the AC input signal is applied to the inverting input node, the stage functions as a positive half-wave rectifier. Two rectifying stages can be interconnected with the collectors of the feedback transistors connected in common to form a full-wave rectifier. The output of the full-wave rectifier can be used to control the gain of an amplifying means producing the AC signal being detected.
