Analogue Filter IP Cores for Design Reuse

1. Bashir Al-Hashimi Reuben Wilcock bmah@ecs.soton.ac.uk rw01r@ecs.soton.ac.uk Analogue Filter IP Cores for Design Reuse

2. Outline • Introduction and Motivations • Analogue Filter IP Core Design • Example Results • Concluding remarks

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

4. Analogue Filter IP Core Design • What are the considerations? • Circuit design technique • Filter Methodology • Automation

5. Solution: Switched Current • Designs based on current mirrors • No linear passive components • Current mode allows low Vdd • High performance cells available Circuit Design Technique • Requirements • Simple, easily designed blocks • No high quality passive components • Compatible with present and future processes • High performance Solution ?

6. Solution: Wave Filters • Ideal for Switched Current • Easily designed blocks • Based on LC ladders • Bilinear transform 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 ?

7. Solution: SKILL tool • Automate hand-calculations • Integrated in Cadence • Manual/Automatic optimisation loops Automation • Requirements: • Increase productivity • Transistor level simulations • Optimisation Solution ?

8. Step 1: Passive Filter Design • De-normalise values • Frequency response • Choose filter type/function/order • Normalised component values

9. Step 2: Wave Filter Design • Decide cutoff/sample ratio • Coefficients are calculated • Optimise [Yufera ’94] • Frequency response from behavioural models

10. Step 3: Memory Cell Design • S2I memory cell [Hughes ’00] • Trade off design parameters • First cut design calculated • DC, transient simulations • Optimise for gm, Cgs, Ctot, Switch Ron and settling

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

12. Schematic Hierarchy • Parameter passing with pPar(“”) • Hierarchy from top to transistor level

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 S2I • May include layout (step 5)

14. Contact Reuben Wilcock Electronic Systems Design Department of Electronics and Computer Science University of Southampton United Kingdom rw01r@ecs.soton.ac.uk