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DC Restoration by a Constant R Symmetrical Passive Lattice

IP.com Disclosure Number: IPCOM000081376D
Original Publication Date: 1974-May-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Dean, RE: AUTHOR [+2]

Abstract

When a readback signal from a magnetic recording head is submitted to integration, the resulting waveform becomes susceptible to a DC component and also to low frequencies. This results in a signal which is not balanced around ground. That is, the DC component and low frequencies cause baseline shifts which result in peak shift and readback errors. Therefore, it is necessary to remove the DC and low-frequency components from the readback signal.

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DC Restoration by a Constant R Symmetrical Passive Lattice

When a readback signal from a magnetic recording head is submitted to integration, the resulting waveform becomes susceptible to a DC component and also to low frequencies. This results in a signal which is not balanced around ground. That is, the DC component and low frequencies cause baseline shifts which result in peak shift and readback errors. Therefore, it is necessary to remove the DC and low-frequency components from the readback signal.

As shown in Fig. 1, the method consists of obtaining the DC and low- frequency components of the input signal, by a low-pass filter 10, and then subtracting those same low frequencies from the signal. Since the low-pass filter introduces a delay, the signal should be delayed by an equal delay 12 so they both arrive simultaneously to the subtractor 14. This in effect results in a special type of low-pass filter having a frequency response, as shown in Fig. 2.

It is apparent that in the output signal, the low frequencies have been greatly attenuated. These frequencies exhibit a very small amount of delay in going through the low-pass filter. Therefore, there is no need to introduce an extra delay. When this happens, it is possible to synthesize the complete transfer function as a linear passive filter. Fig. 3 shows a possible implementation.

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