A current mirror with fast turn-on, for a magnetic disc gated read amplifier

摘要

A switched current mirror provides bias currents for a magnetic disc read preamplifier. The preamplifier may be turned on rapidly from a disabled state. The switched current mirror comprises input and output transistors Q1 and Q2, and is enabled when the signal READ is asserted. When M30 is disabled, the reference current Iref3 is diverted from Q1 to the dummy circuit Q10 so that the capacitor C0 has a potential slightly less than its potential when the mirror is switched on. The transistor M0 is always on, but does not conduct when the mirror is off. The mirror turns on rapidly, with no overshoot.