A Study On Programmable Gain Amplifier And Low-pass Filter For Hard Disk Drive Read Channel

The presented thesis is about broadband programmable gain amplifier and broadband widely tunable continuous time low-pass filter for hard disk drive read channel.The analysis of hard disk drive operating principle and read channel model shows that the programmable gain amplifier with large bandwidth, low gain error and small gain step is needed in the analog front end of hard disk drive read channel. And continuous time low-pass filter with both wide bandwidth variable range and large bandwidth is required as well.Conventional broadband variable or programmable gain amplifier cannot cover the gain accuracy requirement of read channel. On the other hand, high accuracy var-iable gain/attenuation technologies cannot provide sufficient bandwidth or gain step. Two programmable amplifier (PGA) based on two-stage gain control are proposed, which provides both low gain error and small gain step. The first PGA is based on double feedback loops, whose performance at high frequency is improved by intro-ducing compensation network. The bandwidth of the second PGA is increased by Cherry-Hooper amplifier, inductor load and negative Miller capacitor. The two chips are implemented with SMIC 0.13μm CMOS technology. Measurement results show that they both provide gain step of 0.1dB. The bandwidths are 600MHz and 3.8GHz, respectively, and the gain error is -0.03-0.08dB and -0.05-0.04dB, respectively. Both of the PGAs satisfy the gain error and gain step requirements of read channel. The second PGA also meets the bandwidth demand of the read channel.Conventional widely tunable low-pass filters have limited bandwidths, and the tunable ranges of broadband low-pass filters are limited. Quality factor tuning loop is necessary in most of the widely tunable low-pass filter to maintain a constant fre-quency response shape across different bandwidths. A broadband widely tunable low-pass filter consisting of only parasitic capacitors is proposed in this thesis. The transconductance is controlled by transconductor array in the operational transcon-ductance amplifier (OTA). With proper design of the transconductor cell, the trans-conductance and parasitic capacitors are both proportional to the width of input MOS transistor. As a result, the quality factor of the filter can be kept constant by specific design of the ratios between the widths of input transistors in different OTAs, which enables a constant frequency response shape across different bandwidths without quality factor tuning loop. The filter is designed with SMIC 0.13 μm CMOS technol-ogy. Post-layout simulation results shows that its frequency response shape maintains constant with bandwidth from 142MHz to 1.86GHz, which is insensitive to process and temperature variations. The proposed filter satisfies the maximum bandwidth and bandwidth tunable range requirements of read channel.