Write-to-read coupling

Abstract

The design of the interconnect between the read/write heads and the read/write electronics in a disk drive is constrained by the head suspension. The resulting narrow spacing of the write and read lines and the open-line type interconnect that must be used can cause a considerable write-to-read coupling. In storage devices operating at high data rates, the transient voltages on the read line while writing can be large enough to cause electrical overstress of the read head and slow down the recovery from overdrive of the read amplifier. This paper analyzes the coupling mechanisms (magnetic and electrical) for the two write line propagation modes (differential and common). For the low-end of the frequency spectrum, this leads to closed-form lumped parameter expressions. To include the high end of the spectrum, network simulations are presented using distributed parameter coupling as well as distributed parameter write and read lines. The measurement of the severity of write-to-read coupling is discussed. Finally, the paper presents various ways of reducing this write-to-read coupling.