Spezielle Anwendungen des VLSI – Entwurfs Applied VLSI design

Spezielle Anwendungen des VLSI – Entwurfs Applied VLSI design Serialization Heiko Westphal

Serialization • Main idea: save area with reuse of logic • Two possibilities: • Reuse complete components • Operating bit-wise

Serialization: Components • Origin: same as pipelining:each gate just switches once each cycle •  on long path operation time of single gate much smaller than period time  low usage • Idea: increase usage with reusing save gates

Serialization: Components - Example clk Clk(f) Register Clk(2f) Register A C B A B C T-FF Adder MUX MUX A+B A+B Adder Adder Register A+B +C clk Clk(f) Register Register

Serialization: Components - benefit • A bit more than half area when using one component twice: • Area of the component • + Area for control logic • almost the same Period path just increased by control logic • But: 2ndclock with doubled frequency needed for inner register •  more effort than for pipelining •  for our metric not much benefit • Useful for non-critical paths  delay of control does not matter

Serialization: bitwise • Idea: decrease width of components by operating bitwise clk(nf) clk(f) Register Register A1 An B1 Bn MUX MUX log2(n) cIN FA D-FF Counter cOut MUX MUX MUX MUX Register

Serialization: bitwise – benefit • Period: Same up to n-times of original (depends on data dependency) • Problem on area: much effort for serialization and deserialization • 2nd clock needed with frequency n times f •  area reduction only for original logic area >> control logic area • Worst case: area increasment •  only useful in some special cases

Thank you for your attention!

Spezielle Anwendungen des VLSI – Entwurfs Applied VLSI design