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0 pointsderefr3y ago0 comments

Maybe my intuition is completely wrong here, but would the analog case be simplified if the target node+technology was chosen to have trace widths exactly 1/2 the size of the node being transitioned from?

I.e. the traces would have essentially the same standing-wave tuning requirements when modelled as waveguides; would catch a harmonic of the original frequency when acting as antennae; etc.

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monocasa3y ago

Analog isn't just RF; PHYs for weird protocols is a giant component of the space, as well as power monitoring/management. The changes in how voltage/resistance/capacitance/etc work at each node for a given layout is the heavy lift.

Additionally, you very, very rarely have the antenna on chip, and the analog bits even for RF are more signal conditioning that isn't typically modeled like waveguides, but instead more like those old analog plug board computers, simply integrated onto a chip.

derefrOP3y ago

> Additionally, you very, very rarely have the antenna on chip

I didn't mean that there would be components intentionally serving as antennae in a design; more that you might be choosing analog trace lengths in e.g. a modem, or SDR ADC, to minimize harmful analog-domain interference at your bus frequency — i.e. to increase SNR, you're trying to make your traces be as little like an antenna as possible for the frequency bands they're carrying signal in, because you can't just band-pass that interference away.

The nice thing about shrinking by half, in such deigns — I would think — is that if you've already "tuned" your trace paths to a quiet band (for the country the component is being licensed in), then the harmonic frequencies of that band will also be quiet. Otherwise the band's fundamental frequency wouldn't be considered quiet!

(See also: why the unlicensed commercial-use spectrum was allocated to 2.4GHz, and then to 5GHz. 2.4GHz is an obvious choice, already useless for long-range communication due to water in the atmosphere; the other is its equally-useless first harmonic. But the great thing about choosing the first harmonic in particular, is that transmitting at 5GHz isn't putting short-range harmonic noise onto any lower bands that weren't already noisy due to existing commercial use of the fundamental frequency; so you won't suddenly find your other-band devices working worse in the presence of 5GHz transmitters than they already worked due to 2.4GHz transmitters.)

duskwuff3y ago

> I didn't mean that there would be components intentionally serving as antennae in a design

Not an antenna per se, but RF ICs often contain silicon inductors tuned for the operating frequency of the transceiver. Shrinking those down would retune the circuit for a higher frequency.

wbl3y ago

It's not the traces that are the issue but the transistors and resistors. As h_fe goes up new parasitic modes have to be limited. Resistor geometry changes as do the values. Ratiometric design helps but isn't a panacea. And for something like low noise or complex exotic devices you might not even be able to make them with the passes in the new process.

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