Gm Global Technolgoy Operations, Inc.

Delco Electronics Corporation

David W Osburn

David A LaRosa

Richard A Kennedy

Michael John Easterwood

Stephen L Inman

John R Pacourek

James R Knolinski

A method for tuning and aligning an electronically tuned FM broadcast receiver is described. The system described compensates for the mismatch of component values between the antenna and RF amplifier tuned circuits, and the IF offset between the local oscillator frequency and the center frequencies of the antenna and RF resonant circuits by developing independent tuning signals for the circuits. The system also provides temperature compensation, and can be aligned without mechanically adjusting inductors and/or capacitors in the tuned circuits.

Method and apparatus for tuning and aligning an FM receiver

An audio amplifier of the type including circuitry to detect clipping and adjust the gain of an amplifier input element to control the clipping in closed loop operation further includes circuitry effective to sense the temperature of an amplifier component and change the amplifier bias voltage that determines the maximum non-clipping voltage so as to induce clipping in the amplifier when the temperature exceeds a predetermined temperature. The clipping control circuitry then reduces the input gain to the amplifier to control the clipping and, in so doing, reduces power dissipation to a level allowing the temperature to decrease to the predetermined temperature. The circuit provides for closed loop control of amplifier temperature in marginal temperature situations with minimal intrusion on the music reproduction process.

Power limiting audio amplifier temperature protection circuit

Conventional bridged amplifiers obtain output voltage range and DC operating voltage from full and half voltage outputs of a voltage divider. A low voltage unipolar supply powers the voltage divider for small signals. A peak detector selects the higher peak amplifier output; and a voltage follower with an output voltage range from a high voltage unipolar supply maintains an output voltage a predetermined level above the peak. The output of the follower controls a transistor connecting the high voltage supply to the full voltage output of the voltage divider to allow the bridged amplifier outputs to increase above the low voltage supply as necessary in class G operation. An input amplifier obtains output voltage range and DC operating level from the full and half voltage outputs of the voltage divider and has differential outputs connected in opposite phase to the inputs of the bridged amplifiers so that the DC operating level shifts with the output voltage range to maintain an undistorted output across the load in spite of clipped individual outputs due to the lack of oppositely poled supplies. The predetermined voltage is large enough to ensure that the transistor can provide sufficient current from the high voltage supply at high output levels in class G operation.

Class G bridge amplifier with unipolar supplies

A preamplifier circuit for a tape player includes a voltage-follower transistor which is operable when turned on to establish the output bias voltage of the preamplifier circuit at substantially a reference voltage. In turn, a voltage divider network develops the reference voltage coincident with energization of the tape transport mechanism. Due to the inertia of the tape transport mechanism, the speed of the tape remains below that necessary for undistorted operation during a start-up time period immediately following energization of the tape transport mechanism. An RC network is responsive to development of the reference voltage to provide a time delay such that the voltage-follower transistor is prevented from turning on until after expiration of the start-up time period. Thus, the output bias voltage of the preamplifier circuit is not established until the tape speed is sufficient to permit undistorted operation.

Tape player preamplifier circuit responsive to tape speed

A series of electrical signals of a frequency directly proportional to the speed of a motor controlled by a speed control circuit of the type which completes an energizing circuit for the motor through the current carrying electrodes of a switching transistor is generated. These signals are employed to produce a direct current reference potential signal which increases rapidly in magnitude when the motor becomes stalled. The reference potential signal is applied across the series combination of a Zener diode and the base-emitter electrodes of an NPN transistor for supplying base-emitter drive current to the transistor when the potential level thereof reaches a magnitude equal to the inverse breakdown potential of the Zener diode. The collector-emitter electrodes of the NPN transistor are connected in circuit with the motor speed control circuit in such a manner that the control circuit switching transistor is maintained not conductive while base-emitter drive current is supplied to the NPN transistor.

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Kokomo, IN, United States of America

David W Osburn