2031 LP CIRCUIT THEORY

Read Amplifier Circuits

When data is recorded on the disk, a " 1 " bit is represented on the disk by a change in direction of magnetic flux, caused by a change in direction of current passed through the R/W coil in the R/W head. When a "0" bit is to be recorded, no change in current flow direction occurs, causing the direction of the magnetic flux to remain the same on the disk.

When data is being read from the disk, CEMF is induced into the R/W coil by the magnetic fields on the disk, causing current flow which is detected by the read amplifiers. Current flow through the R/W coil will forward bias either CR6 or CR11, depending on the direction. Q3 and CR9 must be forward biased. The first amplifier, UH7, senses this current flow from the R/W coil on one of the inputs and amplifies it. L8, L9, L10, L11, and C1 6 act as a low pass filter, suppressing noise on the amplified output. UH5 is a differential amplifier which amplifies the difference of the two input signals from the filter section. UH4 is a peak detector. The output of UH4 will pulse "high" when a "1" is read. This signal is the reconstruction of data recorded. The time domain filter, UG3 times out when a "1" bit has been read, so unwanted "1" bits are not added to the actual data. The one shot, UG3 generates the correct data pulse width so the read/write logic circuits can convert it to parallel for processor control.