Hard disk drives include a variety of electronic circuitry for processing data and for controlling the overall operation. This electronic circuitry generally includes a preamplifier, a read channel, a write channel, a servo controller, a motor control circuit, read-only memory (ROM), a random-access memory (RAM), and a variety of disk control circuitry to control the operation of the hard disk drive and to properly interface the hard disk drive to a system bus. A separate microprocessor is also generally provided for executing instructions to control the operation of the HDD.
Read channel integrated circuits for hard-disk drive digital magnetic recording channels require a programmable low-pass filter circuit for reducing wideband noise and shaping a readback signal. The low-pass filter is built from a number of tunable transconductance stages. Although a transconductance stage utilizing bipolar transistors can operate at higher frequency ranges than a transconductance stage utilizing MOSFETS and can provide higher transconductance, bipolar transconductance stages of high frequency filters have inherently small linear ranges, which reduces the amplitude of the signal that can be passed through the filter. This small linear range results in lower signal-to-noise performance in the read channel.
Some attempts at increasing the linear range of bipolar transconductance stages have utilized intentional device area offsets. However, affecting the linearity of such devices results in bandwidth degradation due to the use of larger device sizes to effect a device area offset. Generally, the use of larger devices results in diminished frequency response.