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Add option to merge gate contacts in SKY130 (#49)
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* Add option to merge gate contacts in SKY130

* fix TODO
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@rohanku
rohanku authored Oct 15, 2024
1 parent db38d52 commit ceb9a51
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Showing 3 changed files with 82 additions and 50 deletions.
124 changes: 77 additions & 47 deletions pdks/sky130_common_pdk/src/mos.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ use substrate::layout::elements::via::{Via, ViaExpansion, ViaParams};
use substrate::layout::layers::selector::Selector;
use substrate::layout::layers::{LayerBoundBox, LayerPurpose, LayerSpec};
use substrate::pdk::mos::spec::MosKind;
use substrate::pdk::mos::LayoutMosParams;
use substrate::pdk::mos::{GateContactStrategy, LayoutMosParams};

use crate::constants::{
DIFF_EDGE_TO_GATE, DIFF_NSDM_ENCLOSURE, DIFF_NWELL_ENCLOSURE, DIFF_PSDM_ENCLOSURE, DIFF_SPACE,
Expand Down Expand Up @@ -156,55 +156,85 @@ impl Sky130Pdk {
ypoly += FINGER_SPACE;
}

// Place gate contacts and create gate ports
let line = gate_bbox.height();
let space = POLY_SPACE;
let total_contact_len = nf as i64 * line + (nf as i64 - 1) * space;
let gate_span = Span::new(poly_rects[0].p0.y, poly_rects.last().unwrap().p1.y);
// TODO: Should be gridded.
let contact_span = Span::from_center_span(gate_span.center(), total_contact_len);

let mut npc_boxes = Vec::new();

for i in 0..nf as i64 {
let empty_rect = Rect::new(Point::zero(), Point::zero());
let gate_ctp = ViaParams::builder()
.layers(poly, gate_metal)
.geometry(empty_rect, empty_rect)
.expand(ViaExpansion::Minimum)
.build();
let mut gate_ct = ctx.instantiate::<Via>(&gate_ctp)?;

let bot = contact_span.start() + i * (line + space);
let rect = poly_rects[i as usize];
let ofsx = rect.p0.x - gate_bbox.p1.x;
let ofsy = bot - gate_bbox.p0.y;

let ct_ofs = Point::new(ofsx, ofsy);
gate_ct.translate(ct_ofs);
let ct_box = gate_ct.layer_bbox(gate_metal).into_rect();
let mut port = CellPort::new(format!("gate_{i}"));
port.add(gate_metal, Shape::Rect(ct_box));
ctx.add_port(port).unwrap();
gate_pins.push(ct_box);

let npc_bbox = gate_ct.layer_bbox(npc).into_rect();
npc_boxes.push(npc_bbox);

ctx.draw(gate_ct)?;
// Place gate contacts and create gate ports
match params.contact_strategy {
GateContactStrategy::SingleSide => {
assert!(
nf <= 2,
"can only contact nf=2 transistors on a single side"
);
let line = gate_bbox.height();
let space = POLY_SPACE;
let total_contact_len = nf as i64 * line + (nf as i64 - 1) * space;
let contact_span = Span::from_center_span_gridded(
gate_span.center(),
total_contact_len,
ctx.pdk().layout_grid(),
);

let mut npc_boxes = Vec::new();

for i in 0..nf as i64 {
let empty_rect = Rect::new(Point::zero(), Point::zero());
let gate_ctp = ViaParams::builder()
.layers(poly, gate_metal)
.geometry(empty_rect, empty_rect)
.expand(ViaExpansion::Minimum)
.build();
let mut gate_ct = ctx.instantiate::<Via>(&gate_ctp)?;

let bot = contact_span.start() + i * (line + space);
let rect = poly_rects[i as usize];
let ofsx = rect.p0.x - gate_bbox.p1.x;
let ofsy = bot - gate_bbox.p0.y;

let ct_ofs = Point::new(ofsx, ofsy);
gate_ct.translate(ct_ofs);
let ct_box = gate_ct.layer_bbox(gate_metal).into_rect();
let mut port = CellPort::new(format!("gate_{i}"));
port.add(gate_metal, Shape::Rect(ct_box));
ctx.add_port(port).unwrap();
gate_pins.push(ct_box);

let npc_bbox = gate_ct.layer_bbox(npc).into_rect();
npc_boxes.push(npc_bbox);

ctx.draw(gate_ct)?;

let top_npc = npc_boxes.last().unwrap();
let npc_merge_rect = Rect::new(
Point::new(npc_boxes[0].p0.x, npc_boxes[0].p0.y),
Point::new(top_npc.p1.x, top_npc.p1.y),
);
ctx.draw(Element {
net: None,
layer: LayerSpec::new(npc, LayerPurpose::Drawing),
inner: Shape::Rect(npc_merge_rect),
})?;
}
}
GateContactStrategy::Merge => {
let ct_rect = Rect::from_spans(
Span::with_stop_and_length(poly_rects[0].p0.x, 330),
gate_span,
);
let gate_ctp = ViaParams::builder()
.layers(poly, gate_metal)
.geometry(ct_rect, ct_rect)
.expand(ViaExpansion::LongerDirection)
.build();
ctx.draw_rect(poly, ct_rect);
let gate_ct = ctx.instantiate::<Via>(&gate_ctp)?;
ctx.draw_ref(&gate_ct)?;
let ct_box = gate_ct.layer_bbox(gate_metal).into_rect();
let mut port = CellPort::new("gate");
port.add(gate_metal, Shape::Rect(ct_box));
ctx.add_port(port).unwrap()
}
_ => unimplemented!(),
}

let top_npc = npc_boxes.last().unwrap();
let npc_merge_rect = Rect::new(
Point::new(npc_boxes[0].p0.x, npc_boxes[0].p0.y),
Point::new(top_npc.p1.x, top_npc.p1.y),
);
ctx.draw(Element {
net: None,
layer: LayerSpec::new(npc, LayerPurpose::Drawing),
inner: Shape::Rect(npc_merge_rect),
})?;

// Add source/drain contacts
let mut cy = y0;

Expand Down
2 changes: 2 additions & 0 deletions substrate/src/pdk/mos/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -39,6 +39,8 @@ pub enum GateContactStrategy {
Alternate,
/// ABBA placement
Abba,
/// Merge all contacts on one side (usually the left)
Merge,
/// Other; effect depends on layout generator
Other(String),
}
Expand Down
6 changes: 3 additions & 3 deletions substrate/tests/mos.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -12,20 +12,20 @@ fn test_sky130_mos_nand2() {
&LayoutMosParams {
skip_sd_metal: vec![vec![]; 2],
deep_nwell: false,
contact_strategy: substrate::pdk::mos::GateContactStrategy::SingleSide,
contact_strategy: substrate::pdk::mos::GateContactStrategy::Merge,
devices: vec![
MosParams {
w: 200_000,
l: 150,
m: 1,
nf: 2,
nf: 5,
id: MosId::new(0),
},
MosParams {
w: 100_000,
l: 150,
m: 1,
nf: 2,
nf: 5,
id: MosId::new(1),
},
],
Expand Down

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