Amplifiers – With semiconductor amplifying device – Including signal feedback means
Reexamination Certificate
1999-03-30
2001-06-26
Lee, Benny (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including signal feedback means
C330S109000
Reexamination Certificate
active
06252459
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electronic circuits, in particular, the present invention relates to a circuit used in a preamplifier that allows fast recovery from electrical transients.
BACKGROUND OF THE INVENTION
Magnetic read head signal preamplifiers used in hard disk drives typically require fast recovery from electronic transients such as power switching, write to read switching, and thermal asperity. If the preamplifier is unable to recover quickly from transients, then performance of the hard disk drive may be compromised. Power switching occurs when the power is turned on or off. Write to read switching occurs when the disk drive changes functions from writing to the hard disk to reading from the hard disk. A transient such as thermal asperity occurs when a disk drive head hits the disk as the disk goes by. The contact with the disk causes heat on the disk drive head and this heat may show up as a voltage. A thermal asperity may generate a significant amount of energy and only a small fraction of that energy should be processed. These examples of electronic transients typically produce signals that are undesirable to process. If these electronic transients are processed, performance is typically reduced.
Fast recovery from electronic transients, such as power switching, write to read switching, and thermal asperity, is typically achieved via a complicated circuit performing complicated functions, such as dual peak detection and subtraction. Conventional preamplifier circuits that provide fast recovery from transients typically require a substantially large number of components. A large number of circuit devices potentially increase the risk of a device failure in addition to increasing the cost of the circuit.
It would be desirable to allow preamplifiers to quickly recover from electrical transients by integrating a simple circuit. The present invention addresses such a need.
SUMMARY OF THE INVENTION
The present invention is related to a filter circuit that allows preamplifiers, such as those used in hard disk drives, to quickly recover from transients such transients caused by power switching, write to read switching, and thermal asperity. According to an embodiment of the present invention, under normal conditions, such as signals at 100 KHz to 10 MHz, signals at medium frequencies, such as signals at 100 KHz to 10 MHz, pass through a low pass filtering circuit. When a transient signal is received, then a change in voltage for V
out
of the low pass filtering circuit increases by more than 100*V
out
. For example, during transient conditions, the low pass filter circuit may also pass signals ranging from 10 MHz to 100 MHz. Accordingly, under transient conditions, the low pass pole moves approximately 100 times or more. A feedback loop subtracts the resulting low pass signals from the original signal, acting as a high pass filter. The overall circuit recovers quickly from the transient by adjusting for the tail end of the transient. Transient conditions may include a signal that is low frequency or higher amplitude or both. As the transient condition disappears, then the filter circuit resumes normal operation.
A system according to an embodiment of the present invention of filtering a signal in a preamplifier is presented. The system comprising a filter that passes a first range of signals during a first input signal condition and passes a second range of signals during a second input signal condition, wherein the filter produces a first signal, and wherein the second input signal condition includes a transient. The system also includes a differential amplifier coupled to the filter, wherein the differential amplifier subtracts the first signal from a second signal.
A method according to an embodiment of the present invention for filtering a signal in a preamplifier is also presented. The method comprising providing a first signal and determining whether the signal is a transient signal. The method also filters the signal at a first range of frequencies if the signal is not a transient signal, resulting in a first filtered signal; and filters the signal at a second range of frequencies if the signal is a transient signal, resulting in a second filtered signal. One of the first filtered signal and the second filtered signal is subtracted from a second signal.
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Fish & Richardson P.C.
Lee Benny
Nguyen Khanh Van
Siemens Microelectronics, Inc.
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