AND–OR–INVERT (AOI) standard cells and networks are commonly used to implement minimized sum-of-products efficiently. AOI gates are primarily designed to simplify the implementation of which canonical logic form?

Difficulty: Easy

Correct Answer: SOP logic (sum of products)

Explanation:


Introduction / Context:
Many standard-cell libraries include complex gates like AOI (AND–OR–INVERT) and OAI (OR–AND–INVERT) because they reduce transistor count and delay compared to building the same logic strictly from basic gates. Recognizing which canonical form each complex gate targets helps map minimized expressions directly to efficient hardware.

Given Data / Assumptions:

  • AOI topology: multiple AND gates feed an OR gate, followed by an inversion.
  • Target expressions: minimized two-level SOP forms (sum of products).
  • Goal: identify which canonical form AOI matches most naturally.


Concept / Approach:
A two-level SOP is of the form F = Σ(products) = (A*B) + (C*D) + … . AOI realizes the complemented SOP: F' = [(A*B) + (C*D) + …]'. In CMOS, AOI gates can be highly efficient because the pull-down (or pull-up) networks implement the inverted sum directly with fewer transistors. By placing or removing bubbles (De Morgan transformations), an AOI gate effectively implements the intended SOP with minimal staging, often as a NAND–NAND equivalent.

Step-by-Step Solution:

Start from SOP: F = P1 + P2 + … where Pi are product terms.Implement OR of ANDs feeding an inverter: X = (P1 + P2 + …)'.Use bubble pushing/De Morgan to match signal polarities so that X' = F is obtained at the desired node.Thus AOI maps directly to SOP with high efficiency.


Verification / Alternative check:

Compare gate/transistor counts for a typical 4-term SOP: AOI often reduces both delay and area versus discrete AND + OR + INV stages.


Why Other Options Are Wrong:

POS: OAI structures are typically better aligned with POS (sum terms feeding an AND followed by inversion).De Morgan’s theorem: It is a transformation tool, not a canonical target form.NAND-only logic: While AOI can be equivalent to NAND–NAND, the design goal is efficient SOP implementation.


Common Pitfalls:

Confusing AOI with OAI; remember AOI corresponds to SOP, OAI to POS.Forgetting that the final inversion in AOI is part of the cell and can be absorbed depending on signal polarity needs.


Final Answer:

SOP logic (sum of products)

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