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Subtractor /Multiplier. Section 4.5 & 4.7. Outline. Delay Four Bit Subtractor Multiplier. Four Bit Adder. Erroneous Results When Delay is inserted in half_adder.v. Four-Bit Adder. C 4 is calculated last because it takes C 0 8 gates to reach C 4 .

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Subtractor /Multiplier

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subtractor multiplier


Section 4.5 & 4.7

  • Delay
  • Four Bit Subtractor
  • Multiplier
four bit adder1
Four-Bit Adder

C4 is calculated last because it takes C0 8 gates to reach C4.

Each FA uses 2 XOR, 2 AND and 1 OR gate.

A four-bit adder uses 8 XOR, 8 AND and 4 OR gate.

build a full adder circuit
Build a Full-Adder Circuit






One gate-delay

verilog and jobs
Verilog and Jobs

Job: Mixed signal design job in San Jose, CA

Level: BS/MS in EE

  • Job Description:

We are seeking a Mixed-Signal ASIC Verification Engineer. The successful candidate will be a key member of the team developing custom ICs for display modules based on the QMT SMI display technology. Hands on technical contributor in verification of Mixed-Signal ASICs and IP development projects. A candidate will help architect, specify, and lead the implementation of mixed Analog/Digital verification projects using high level verification languages. You will work very closely with analog circuit design team, digital design team, and mixed-signal ASIC project leaders to implement complete verification environments and methodologies. Design Mixed-Mode testbenches using SystemVerilog, create VerilogAMS models for analog circuit, create checkers, use ADE/Irun environment to simulate and execute tests in NCSIM/SimVision. Log results and verify with automatic checker.

Responsibilities: Create re-usable AMS testbenches from grounds up using advanced verification methodologies (like UVM, OVM etc.) with emphasis towards behavioral modeling of analog blocks, closed-loop simulation with digital design and analog behavioral models and/or transistors by using Cadence Virtuoso schematic editor and ICFB tool environment, and automated & coverage-driven verification. Develop and maintain behavioral models (VerilogA/VerilogAMS) of analog and mixed-signal blocks including data converters(ADC/DAC), power converters (charge pump, buck converter, boost converter), switch mode power supplies, LDOs, analog switches/muxes, PLLs, level-shifters, amplifiers, thermal sensors.

verilog and fpga
Verilog and FPGA

Parker Aerospace, an operating segment of Parker Hannifin Corporation, is one of the world’s leading producers of flight control, hydraulic, fuel, inerting, fluid conveyance, thermal management, and engine systems and components for the aerospace industry. We design and build equipment for virtually every aircraft and aero engine being produced in the world today.



Responsible for design, verification and certification of FPGA based aerospace firmware. Requirements creation and validation, conceptual design, detail design and testing. Create control circuits, design (writing of VHDL), develop timing constraints, simulate (functional and timing), place and route synthesized designs. Ensure all required data items and artifacts to support FAA SIO audits are correct and complete. Creation of verification requirements based test cases and oversight of verification simulations by supplier. Verify test cases, procedures, and test benches are created to satisfy existing design requirements. Perform independent audit of verification artifacts. Participate in peer design reviews and support continuous process improvements.

Bachelor’s Degree in Electrical Engineering or related engineering discipline with preferably six plus years of experience in the design, development and certification of aerospace firmware. A Master’s Degree is a plus. Specific experience in DO-254 certification required. Specific experience in motor drive and flight control applications is a plus. Experience with ARINC-429, CAN, SPI or other serial interfaces. Experience in requirements capture and validation. Experience with VHDL design and verification. Experience with Xilinx and Altera development tools. Experience with ModelSim/QuestaSim to perform simulation and debug of VHDL design. Experience with in-circuit verification techniques. Possess excellent trouble shooting skills and knowledgeable in Chipscope / Signal Tap FGPA debugging tools. Experience creating requirements based test cases. Experience creating simulation / verification test bench using VHDL / Verilog language. Experience in supporting FAA SOI audits. Leadership experience a plus. Strong technical writing, verbal and written communication skills. Excellent work ethic. Able to work well in teams (local as well as remote) and is self-motivated.

unsigned number
Unsigned Number

(2-bit example)

unsigned addition1
Unsigned Addition
  • 1+3=

(Indicates Overflow)

(Carry Out)

Overflow can be an issue in unsigned addition.

unsigned subtraction 1
Unsigned Subtraction (1)
  • 1-2=

(1’s complement)

(2’s complement)

summary for unsigned addition subtraction
Summary for Unsigned Addition/Subtraction
  • Overflow can be an issue in unsigned addition (An overflow is detected from the end carry out of the most significant position)
  • Unsigned Subtraction (M-N)
    • If M≥N, and end carry will be produced. The end carry is discarded.
    • If M<N,
      • Take the 2’s complement of the sum
      • Place a negative sign in front
four bit adder subtractor
Four-Bit Adder-Subtractor

For detecting

overflow in unsigned


For detecting overflow in addition/subtraction of signed numbers

the mode input 1
The Mode Input (1)

If M=0, =

If M=1, =


the mode input 2
The Mode Input (2)

If M=0,

If M=1,

m 1 subtraction
M=1 (Subtraction)


2’s complement is generated of B is generated!

four bit adder subtractor1
Four-Bit Adder-Subtractor














sample output of adder subtractor circuit
Sample output of adder/subtractor circuit

Ignore V if you are working with unsigned numbers.

two bit binary multiplier
Two-Bit Binary Multiplier



hardware correlation1
Hardware Correlation