Platform-based Design for Mixed Analog-Digital Designs

1. Platform-based Design for Mixed Analog-Digital Designs r2 rM=WM/LM L2 W2 P System Specs SystemLevelExploration IB VGS2 ½ Define a formal setof conditions for feasibility System Design • Matlab/Simulink, V-AMS, … • Breakdown Requirements n Select new topology n ½ W4  + - I Derive ACG and nominal configuration Analog Platform + - L4 Define an objective function for optimization out VGS4 Circuit Sizing &Synthesis Circuit design • Size, Simulate and iterate Generate P Optimize system constraining behavioral models to their P Layout design • Verify and iterate Refine/Add platforms • Performance models are approximated with Support Vector Machines (SVMs) • n-dimensional functions that evaluate to {0,1}, 2D projection shown aside • Characterization cost C  #sim · Tsim  kdim(I) · Tsim • Constrain Iwith Analog Constraint Graphs so that effective dimensionality is drastically reduced • Exploit ACGs to bias characterization • A tool set is available to generate performance models Run local optimization to meet requirements Return optimal performancesand candidate solutions • Export non-idealities at system level • Fast, reasonably accurate simulations for system exploration • Built for Top-down use Behavioral models Analog Platform • Constrain behavioral models to implementation architecture • Accurate models obtained through bottom-up characterization of platform Performance models Interconnection models • Model analog component composition • Allow composing systems from APs maintaining performance accuracy • Encapsulate analog components providing an abstraction level consistent with platform based design paradigm • Implement function/communication/architecture mapping in the analog context • Provide accurate performance estimation for optimization through constraints propagation Define behavioral model and P • Multi-stage gm/gm wide-band amplifier • Top-level design problem: • determine optimal configuration (#stages and gain distribution) so to minimize power • First step: behavioral model • Second step: Interconnection model ( Cload) • Third step: Performance model System Requirements • Exploit Platforms for optimizing the system • Formulate as an optimization problem at behavioral level • Constrain instances with APs • Perform optimization (SA) • Return feasible specs and candidate instances Select new topology … Derive ACG and nominal configuration Generate P Architectural Space • Define the platform library for the system • New topologies can be easily added and compared through the exploration-through optimization top-down flow • Given a circuit topology, performance characterization defines the platform architectural space • Performance models allow selecting feasible points in the architectural space • The framework is the same as for digital platforms  capture mixed signal designs • Decouple circuit from system design • Harness designer creativity exporting several circuit topologies at the system level • Platforms do not solve circuit synthesis problem directly, they export circuits at system level Build System with APs • Performance models allow defining multiple levels of abstraction • Performance models map the architecture space I of level i into the architecture space P of level i+1 • For a circuit platform i: • I is the set of n-tuples (I Rn) {W1, W2, …, L1, L2, …, IB1, …, VB1, ..} • O is the set of m-tuples (O Rm){Power, Gain, NF, IIP3, P-1dB, DR,…} • : Rn Rm is the AP Evaluation function • analytical expressions, simplified simulations, Spice simulations • A performance model is a relation P s.t. P(x)=1  x(I) • Set a well defined design problem • Automatic exploration needs formal definition for working systems • Optimize the system and refine the architectural blocks – Architectural exploration is performed Fernando De Bernardinis, Yanmei Li, Alberto Sangiovanni-Vincentelli Performance Models Platform Characterization Abstract A design methodology for system level analog design is proposed. Analog Platforms provide a new abstraction layer that allows fast while accurate evaluation of analog components at the system level. Analog Constraint Graphs (ACGs) are introduced to make the approach more efficient. The basic idea and design flow of Platform-based Analog Design are presented. A multi-stage amplifier design is discussed as a proof-of-concept example. Design Example: Bottom-Up Analog Platform Design Paradigm AP Design Flow: Bottom-up Phase Top-down Phase Top-down May 10, 2004