Truth Table

Verilog Design Code

// Pantech e-learning

// NAND gate using dataflow modeling

module nand_gate(

  input a,

  input b,

  output y

);

  assign y = !(a & b);

endmodule

Testbench Code

// Pantech e-learning

module nand_gate_tb;

  reg a, b;

  wire y;

  nand_gate uut(

    .a(a),

    .b(b),

    .y(y)

  );

  initial begin

    $dumpfile(“dump.vcd”);

    $dumpvars;

    a = 1’b0; b = 1’b0;

    #10 a = 1’b0; b = 1’b1;

    #10 a = 1’b1; b = 1’b0;

    #10 a = 1’b1; b = 1’b1;

    #10 $finish;

  end

endmodule

Waveform Output

The output waveform clearly shows high (1) output for all cases except when both inputs are 1, which results in a low (0)—validating the NAND gate behavior.

                                                                        Figure: NAND gate simulation output

Applications

• Used in memory circuits like SRAM and DRAM
• Core of universal gate logic design
• Found in timers and oscillators
• Preferred in CMOS design due to lower transistor count
• Helps build combinational and sequential circuits

Frequently Asked Questions (FAQs)

Q1: Why is the NAND gate considered efficient in digital design?
A1: It uses fewer transistors and is capable of implementing any logic function, saving space and cost.

Q2: What happens if both NAND gate inputs are unknown (X)?
A2: The output becomes X, signaling uncertainty and aiding in simulation debugging.

Q3: Can a NAND gate be used to create other gates?
A3: Yes, it’s a universal gate that can construct NOT, AND, OR, XOR, and more.

Q4: What is the output if one input is 0 and the other is X?
A4: Output is 1 since 0 AND X equals 0, and NAND inverts that to 1.

Q5: Why use a NAND gate instead of an AND gate in fault-tolerant logic?
A5: NAND’s default output is 1, which is often considered a safe or inactive state, making it safer in critical systems.

Conclusion

The NAND gate is not just a basic digital component—it is a gateway to building complex logic using simple principles. By simulating it in Verilog and observing its behavior, you’ve taken a key step toward mastering digital design.

Call to Action

Experiment further by deploying this design on a MAX10 FLK FPGA board from Pantech eLearning.

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