A low-power CMOS VGA for 50 Mb/s disk drive read channels

We describe an all CMOS variable gain amplifier (VGA) suitable for use in disk drive read channels. The VGA maintains a 3 dB bandwidth greater than 85 MHz throughout its gain range. This ensures good phase linearity for data transfer rates of up to 50 Mb/s. The VGA provides a 25 db gain variation along an ideal exponential gain to control voltage curve and 30 dB of gain control if ideal exponential characteristics is not absolutely necessary. The VGA achieves the necessary exponential gain to control voltage characteristics intrinsically using only MOS transistors as a single unit to reduce power and area consumption. Overall power consumption is less than 10 mW for the VGA circuit excluding the off-chip buffer circuits