An eight-order lowpass filter with 5 - 100 MHz tuning range and programmable boost

An eighth order linear phase continuous time low-pass filter implementing pulse shaping and noise filtering for partial response maximum likelihood (PRML) read channel applications is presented. The filter supports two operation modes: DATA and SERVO. In each mode the cutoff frequency is tunable in a 1 to 3 range for a fixed external reference resistor (a further 1 to 3.3 tuning range is available changing this resistor), the cutoff frequency range in SERVO is an half that in DATA. The amount of boost is programmable in the 6-15dB range for DATA and 3-9dB for SERVO. At the nominal signal swing of 100mVpp differential, the allowed distortion is 1%. The transconductance capacitance (Gm-C) filter is implemented in a 0.35µm 3.3V BiCMOS technology, occupies 0.14mm²and dissipates 46mW at 100MHz.