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AC Coupling With Improved Phase/Bandwidth

IP.com Disclosure Number: IPCOM000061623D
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Martin, VC: AUTHOR

Abstract

This AC coupling is used between the amplifier stages of a disk file read channel. The coupling blocks out DC offset and filters out low frequency noise. The improved phase characteristic of this pole/zero configuration permits locating the low frequency cutoff four to five times closer to the lowest signal frequency. Transient recovery time and low frequency noise attenuation are thereby optimized (e.g., read channel recovery from a write turn-off transient). Implementations (A) and (B) are similar, where R2 represents driver resistance in (A) and shunt load resistance in (B). In (A), an inductor is added in series with the normal AC coupling resistor. This is a minimum space passive implementation, but inductors are expensive and prone to picking up noise. Implementation (C) requires only resistors and capacitors.

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AC Coupling With Improved Phase/Bandwidth

This AC coupling is used between the amplifier stages of a disk file read channel. The coupling blocks out DC offset and filters out low frequency noise. The improved phase characteristic of this pole/zero configuration permits locating the low frequency cutoff four to five times closer to the lowest signal frequency. Transient recovery time and low frequency noise attenuation are thereby optimized (e.g., read channel recovery from a write turn-off transient). Implementations (A) and (B) are similar, where R2 represents driver resistance in
(A) and shunt load resistance in (B). In (A), an inductor is added in series with the normal AC coupling resistor. This is a minimum space passive implementation, but inductors are expensive and prone to picking up noise. Implementation (C) requires only resistors and capacitors. This passive implementation avoids inductors at the cost of two resistors and one capacitor, but it also attenuates the signal. Note the criterion for good phase performance,
i.e., R1 = R2 = R3 and 1 < C1/C2 < 1.3. Implementation (D) uses two resistors, two capacitors and an amplifier of K = 1, a simple emitter follower. This implementation avoids both inductors and signal attenuation at the cost of one resistor, one capacitor and an active element. All implementations are effective, and choice depends on board space and preference for inductors.

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