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Fourth Order Low-Pass Filter ASIC

This IC, commonly refered to as "The Decimator", implements a fourth order (sinc4) digital low-pass filter. The intended application for this filter is to process output data from a multi-bit sigma-delta modulator, thus completing a high-resolution A/D converter system.

The entire design was completed in approximately 10 weeks in the Fall of 1993 by me (Paul Stoffregen), Shivani Gupta, and Srinivas Pattamatta as the project associated with the OSU-ECE graduate VLSI design course (ECE 517) instructed by Richard Schreier.

This full-custom CMOS layout was drawn using the CMOSN lambda-based design rules. The layout preview shown here is also available in medium, large, and huge sizes. After the course, the chip was fabricated by MOSIS using Orbit's 2um P-well process on a tiny-chip (2.2mm by 2.2mm) die.

chip All four chips fabricated by MOSIS were tested (at only moderate speed) using a microcontroller to feed data into the chip and collect the output. All four chips produced correct output results!

die photo

Content by Subject

  • Intended Application
  • Original Project Specification
  • Cronological History of the Design Process
  • Architectual Overview
  • Detailed Design Overview
    • 24 Bit Adder and Registers
    • Parallel to Serial Shift Register
    • Serial Subtractors and Shift Registers
    • Control State Machine
  • CMOSN Layout (downloadable)
  • Testing the Chips (all four did function correctly)

Fourth Order Low-Pass Filter IC with Decimation Factor of 32 (aka "The Decimator")
Paul Stoffregen - Circuit Design, IC Layout, Spice Simulation
Shivani Gupta - Schematic Entry, Switch-Level Simulation
Srinivas Pattamatta (aka PVS) - Spice Simulation, Fiddling with CAD Software
Richard Schreier - Project Specification, Architecture Outline, Free Pizza
Last updated: February 24, 2005