XNOR gate

Input Output
A B A XNOR B
0 0 1
0 1 0
1 0 0
1 1 1

The XNOR gate (sometimes, EXNOR, ENOR, and, rarely, NXOR, XAND) is a digital logic gate whose function is the logical complement of the exclusive OR (XOR) gate. The two-input version implements logical equality, behaving according to the truth table to the right. A high output (1) results if both of the inputs to the gate are the same. If one but not both inputs are high (1), a low output (0) results. The algebraic notation used to represent the XNOR operation is .

Symbols

There are 2 symbols for XNOR gates: one with distinctive shape and one with rectangular shape and label. The distinctive symbol for the XNOR gate is that of the XOR gate with an added inversion bubble.

Distinctive symbol
Rectangular symbol

The XNOR gate with inputs A and B implements the logical expression .

Hardware description and pinout

XNOR gates are represented in most TTL and CMOS IC families. The standard 4000 series CMOS IC is the 4077 and the TTL IC is the 74266. Both include four independent, two-input, XNOR gates. The pinout diagram is as follows:

Pinout diagram of a 74266 quad XNOR DIP-format IC.

  1. Input A1
  2. Input B1
  3. Output Q1
  4. Output Q2
  5. Input B2
  6. Input A2
  7. Vss (GND)
  8. Input A3
  9. Input B3
  10. Output Q3
  11. Output Q4
  12. Input B4
  13. Input A4
  14. Vdd (Vcc)

This device is available from most semiconductor manufacturers such as NXP. It is usually available in both through-hole DIP and SOIC format. Datasheets are readily available in most datasheet databases. DIL is a dual in-line package, and SIL is a single in-line package.

Alternatives

If no specific XNOR gates are available, one can be made from four NOR gates or five NAND gates in the configurations shown below. In fact, any logic gate can be made from combinations of only NAND gates or only NOR gates.

XNOR gate constructed using only NOR gates
XNOR gate constructed using only NAND gates
XNOR gate can be made with 3 gates (1× OR & 2x NAND gates)

See also

References

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