Electronic Systems Design Group Department of Electronics and Computer Science University of Southampton, UK Analogue Filter IP Cores for Design Reuse Bashir Al-Hashimi Reuben Wilcock

ASP 2002 University of Southampton, UK Slide 2 Outline Introduction and Motivations Analogue Filter IP Core Design Example Results Concluding remarks

Reuben WilcockASP 2002 University of Southampton, UK Slide 3 Introduction System on Chips (SoC) employ IP cores Analogue IP core design is demanding –Difficult to trade as high level description –Correct operation depends on many factors Important to redesign for particular specifications and process to ensure functionality

Reuben WilcockASP 2002 University of Southampton, UK Slide 4 Analogue Filter IP Core Design What are the considerations? Circuit design technique Filter Methodology Automation

Reuben WilcockASP 2002 University of Southampton, UK Slide 5 Solution ? Circuit Design Technique Requirements –Simple, easily designed blocks –No high quality passive components –Compatible with present and future processes –High performance Solution: Switched Current –Designs based on current mirrors –No linear passive components –Current mode allows low Vdd –High performance cells available

Reuben WilcockASP 2002 University of Southampton, UK Slide 6 Solution ? Filter Methodology Requirements –Suitable for Switched Current –Regular structures and simple design procedure –Based on LC ladder to inherit low sensitivity –Bilinear transform so Nyquist limit can be approached Solution: Wave Filters –Ideal for Switched Current –Easily designed blocks –Based on LC ladders –Bilinear transform

Reuben WilcockASP 2002 University of Southampton, UK Slide 7 Automation Requirements: –Increase productivity –Transistor level simulations –Optimisation Solution ? Solution: SKILL tool –Automate hand- calculations –Integrated in Cadence –Manual/Automatic optimisation loops

Reuben WilcockASP 2002 University of Southampton, UK Slide 8 Step 1: Passive Filter Design De-normalise values Frequency response Choose filter type/function/order Normalised component values

Reuben WilcockASP 2002 University of Southampton, UK Slide 9 Step 2: Wave Filter Design Optimise [Yufera ’94] Frequency response from behavioural models Decide cutoff/sample ratio Coefficients are calculated

Reuben WilcockASP 2002 University of Southampton, UK Slide 10 Step 3: Memory Cell Design S 2 I memory cell [Hughes ’00] Trade off design parameters First cut design calculated DC, transient simulations Optimise for gm, Cgs, Ctot, Switch Ron and settling

Reuben WilcockASP 2002 University of Southampton, UK Slide 11 Step 4: Complete Filter Design Save all design variables, dimensions and coefficients to a single file Schematic representing entire transistor level design is opened Spectre RF used to give an AC response in minutes Revisit steps 1 – 3 as necessary

Reuben WilcockASP 2002 University of Southampton, UK Slide 12 Schematic Hierarchy Parameter passing with pPar(“”) Hierarchy from top to transistor level

Reuben WilcockASP 2002 University of Southampton, UK Slide 13 Conclusions Switched Current has good potential for IP cores Wave is suitable as a filter methodology Automation tools should be integrated into powerful CAD packages Our tool allows a designer to rapidly develop Switched Current analogue filter cores. Future work will involve –Extending the filter library –Including Class AB cell as alternative to S 2 I –May include layout (step 5)

Reuben WilcockASP 2002 University of Southampton, UK Slide 14 Contact Reuben Wilcock Electronic Systems Design Department of Electronics and Computer Science University of Southampton United Kingdom