Cirrus Logic Inc.

Marvell Technology Group Ltd.

Wen Fang

Gani Jusuf

Low-noise magneto-resistive (MR) pre-amplifier circuit amplifies signal from MR head. MR head is biased at optimal point by current source to generate signal. Current source is powered by regulator to reduce noise contribution from Vcc due to finite output impedance of current source. Self-biased CMOS low-noise amplifier (LNA) minimizes input-referred noised without using negative power supply. Small MOS transistor with feedback tracking loop replaces self-bias resistor which determines lower corner cutoff frequency. This facilitates use of large-value resistor, thereby enabling on-chip integration of DC blocking input capacitor. Gm&mdash;Gm amplifier configuration increases gain bandwidth product and minimizes parasitic effects of MOS transistors.

Low-noise magneto-resistive amplifier using CMOS technology

According to the present invention, a PLL circuit is designed to include an active mode, a sleep mode and an idle mode. In the idle mode, the PLL draws substantially less power than that in the active mode. In order to return to the designed operating frequency immediately, the PLL periodically refreshes itself in this mode of operation. The power consumption of the PLL is dependent upon the ratio of on-time to off-time which is a fraction of the power consumed in the active mode. Preferably, the PLL is designed to receive an external clock signal as a reference clock from which it develops the internal system clock. The PLL also receives a lower frequency refresh signal for activating a refresh operation during the idle mode. The PLL can power itself down after completing a single phase compare operation. The refresh signal which can be derived from a real time clock must be synchronized to the external reference clock. Thus, the PLL includes a zero-phase-restart circuit.

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Fremont, CA, United States of America

Wen Fang