Amplifiers – With semiconductor amplifying device – Including signal feedback means
Patent
1991-09-03
1993-02-02
Mullins, James B.
Amplifiers
With semiconductor amplifying device
Including signal feedback means
330 85, 330107, 360 67, H03F 134
Patent
active
051840901
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a head amplifier for use with a home VTR, more specifically, to a head amplifier suitable for integratin into an IC.
A head amplifier is an amplifier for a home VTR which processes playback signals from a magnetic head. A head amplifier installed in an IC is disclosed, for example, in Japanese Laid-Open Publication No. 55-153108. The head amplifier of this publication has several disadvantages which will be detailed hereinbelow.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a head amplifier which overcomes the drawbacks of the prior art.
It is a further object of the invention to provide a head amplifier which includes a frequency-sensitive negative feedback path to permit use of PNP transistors, without the normal phase degradation resulting from such components.
It is a still further object of the invention to provide a head amplifier that uses a frequency-sensitive differential amplifier to cancel DC voltage offsets, and to maintain relatively constant response over an effective frequency band. The AC response rolls off at low frequencies to suppress unwanted low frequency noise.
Briefly stated, the present invention provides a head amplifier that is integrated into an IC with a minimum number of pins and outside parts as well. An offset cancellation circuit cancels offset voltages to prevent distortion of playback signals. An amplifier amplifies a playback signal to produce an output signal that is fed to one input of a differential amplifier. A reference voltage is fed to the second input of the differential amplifier. The input of the differential amplifier is compared in a comparator with the reference voltage to produce a feedback signal for cancelling offset voltages. The feedback path is frequency sensitive to reduce frequency response at low frequencies, and to compensate for distortions produced at high frequencies from using PNP transistors in the comparator.
According to an embodiment of the invention, there is provided a head amplifier comprising: an amplifier effective for producing an output in response to a playback signal from a head, a differential amplifier, means for feeding the output to the differential amplifier, means for producing a reference voltage, means for feeding the reference voltage to the differential amplifier, comparator for comparing the output with the reference voltage, and means for feeding back an output of the comparator to an input of the amplifier.
According to a feature of the invention, there is provided a head amplifier comprising: an amplifier for amplifying a playback signal from a head to produce an output signal, a differential amplifier responsive to a difference between the output signal and a reference voltage to produce an amplified output signal, a feedback circuit, means in the feedback circuit for comparing the amplified output signal with the reference voltage and feeding back a feedback signal to the amplifier, and means in the feedback circuit for amplifying the feedback signal with a high gain when a frequency of the amplified output signal is lower than an effective frequency band and amplifying the feedback signal with a smaller gain than the high gain when the frequency of the amplified output signal is higher than the effective frequency band.
The present invention comprises an amplifier which receives a playback signal from a head, a differential amplifier which amplifies the output of the amplifier, a comparator which compares the output of the amplifier with the reference voltage, and a feedback means which returns the output of the comparator. An offset between the two inputs to the differential amplifier is forced to zero by the output of the comparator being feed back to the amplifier.
The present invention also has a means creating a frequency characteristic in a feedback path; this means includes the comparator and the feedback means. This eliminates noise in the playback signal.
The above, and other objects, features and adv
REFERENCES:
patent: 4518925 (1985-05-01), Fukasawa
Mullins James B.
Sanyo Electric Co,. Ltd.
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