差分对版图(Didfferential Pair Layout)

Basic Differential Pair Layout

1-Basic-Differential-Pair-Layout

Good matching in the absence of cross-chip gradients; both drain currents flow in same direction.


Alternative Differential Pair Layout

2-Alternative-Differential-Pair-Layout

More compact, but worse matching than previous case; drain currents flow in opposite directions.


Common Centroid Layout

3-Common-Centroid-Layout

Q1 and Q2 have a “common centroid”, which makes them immune from cross-chip gradients. Best matching performance possible.


Alternative Common-Centroid Layout

4-Alternative-Common-Centroid-Layout

Immune from cross-chip gradients like previous case, but area is saved by sharing sources.


Differential Pair with Very Wide Transistors

5-Differential-Pair-with-Very-Wide-Transistors

Very wide transistors can lead to awkward layout and significant series gate resistance.


Multi-Finger Transistors

6-Multi-Finger-Transistors

Multi-fingered gates save space and reduce series resistance in gate. Notice that drains are selected to minimize parasitic capacitance to bulk.


Common Centroid Layout with Multi-Fingered Gates

7-Common-Centroid-Layout-with-Multi-Fingered-Gates

Drain-to-bulk parasitic capacitance is minimized; sources are partially shared to save area.


“Doughnut” Transistors

8-Doughnut”-Transistors

Gives the minimum Cgd (gate-to-drain overlap) and Cdb (drain-to-bulk) parasitic capacitances for a given W/L ratio. May be used to minimize Miller effect when high speed is desired and a dominant pole is created elsewhere.

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