Loading the page
Loading
Loading
Lesson 11
A chip's ground isn't the board's. A few nanohenries of pin and bond wire sit between them, and when outputs switch together their current all comes home through it. Commit to how far a quiet output rides up, then fire up the scope. Lesson 10, Edges and reflections, is the same board one step out: what the edge does once it leaves the pin.
Predict · 1 of 2 · the quiet line
Eight outputs of a 3.3 V buffer switch high to low together, each into 50 pF, with 1 ns edges. Their current all comes home through one 5 nH ground pin. A ninth output is held low. What peak voltage does that quiet output reach at the board? CH1 is one of the switching outputs.
Result
Waiting on your call.
Make your mark, then lock it in. The answer, your error and the reason behind it land here, and the scope and every view below fire up.
Engine: in-browser MNA solver, one edge from the DC point in 2,304 trapezoidal steps; the 8 switching outputs as one exact branch (Ron/N, L/N, N·C), checked against every output built separately; the die's ground against the closed form of a ramp into a series RLC, within 5·10⁻⁴ of its peak (the check's tolerance) · the budget map by superposing one ramp response per row · SPICE: its numbers show once you're in the lab (they'd give the answers away) · the driver a TI SN74LVC244A (its Ron from VOL), a fixed Ron; receivers and clamp diodes left out; the package assumed, pins uncoupled (see How it works).