An arrangement to provide feedback to amplifier systems incorporating an electrical load. A current transformer in conjunction with a resistor is incorporated 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 provides a single-ended amplifier driving a load and incorporates the current transformer between the output of the amplifier and the load. The secondary winding of the transformer is in series with the input to the amplifier, and a resistor is connected across the secondary winding. The transformer determines the frequency bandwidth of the entire amplifier system, and the resistor value determines the gain of the amplifier. Such a configuration provides negative feedback to the amplifier which is directly proportional to changes in current in the load due to distortions caused by the amplifier or load. The second embodiment applies the principles of the present invention to a differential amplifier configuration. The primary winding of the current transformer is connected between the output of the amplifier and one end of the load. A secondary winding of the transformer is connected to the other end of the load and to the negative input of the differential amplifier. A resistor is connected across the secondary winding of the transformer.
A transformer coupled amplifier circuit that eliminates transformer induced non-linearities by way of a dual feedback path without sacrificing any of the inherent attributes of general transformer coupled amplifiers.
By the use of a feedback arrangement, deleterious circuit effects of an isolation transformer in a terminal device for a telephone line can be eliminated. By this arrangement, a smaller, cheaper transformer may be used. A terminal device employing such arrangement can present a balanced termination to a telephone line, exhibit a known and controlled impedance to that line and provide for signals to be coupled to and from that line.
An active aerial for use in car radios and aerial "arrays" comprising an aerial element and an aerial connected thereto. In order to obtain a low distortion and a good signal-to-noise ratio in spite of the presence of protection diodes to prevent overloading of the amplifier by atmospherics and in spite of contamination of the aerial etc, the input of the active portion of the amplifier is virtually grounded. To this end, the amplifier is preferably an operational amplifier having a high gain factor, the signal input of which is connected to ground, both the signal coming from the aerial element and a signal fed back from an output of the amplifier being applied to the inverting signal input.
A driver circuit for applying a first signal having a desired wave form, frequency and peak to peak voltage to a coaxial transmission line which also has applied to it a second signal having a substantially higher frequency. An operational amplifier has the first signal applied to its noninverting input terminal. The output of the operational amplifier is applied across the primary winding of a driver coupling transformer through an inductor which provides high impedance to the second signal. The voltages induced in the secondary winding of the driver transformer are applied to the transmission line. The primary winding of a feedback transformer is connected in parallel with the secondary winding of the driver transformer. The voltage induced in the secondary winding in the feedback transformer are applied by a feedback circuit including an R.C. filter to the inverting input terminal of the operational amplifier. The signal applied to the inverting input terminal includes both an A.C. component and a D.C. component, which components cause the output current of the operational amplifier to induce in the secondary winding of the driver transformer a signal, the wave form, frequency and peak to peak voltage of which substantially equal those of the first signal applied to the noninverting input terminal of the operational amplifier.
