Digital Circuits: Flip Flops and Latches

Flip Flops

• Definition: Flip flops are bistable circuits that can hold one of two states.

• Types:

  • SR Flip Flop: Set-Reset, basic flip flop with two inputs (Set and Reset).
  • JK Flip Flop: Extension of SR, can toggle states based on inputs.
  • D Flip Flop: Data flip flop, captures the value of the data input (D) on a clock edge.
  • T Flip Flop: Toggle flip flop, changes states on each clock pulse when T input is high.

• Functionality:

  • Each flip flop has a clock input which triggers state changes.
  • Output depends on the current state and the inputs.

• Applications:

  • Data storage (registers)
  • Frequency dividers in digital circuits
  • State machines in sequential logic.

Latches

• Definition: Latches are level-sensitive devices that can store one bit of data.

• Types:

  • SR Latch: Similar to SR flip flop but operates without a clock; it changes state while inputs are active.
  • D Latch: Captures the input value when the enable signal is active.

• Functionality:

  • Latches are transparent when enabled, meaning output follows the inputs.
  • They maintain their state when the enable is deactivated.

• Applications:

  • Temporary data storage
  • Level-sensitive memory elements
  • Building blocks for more complex memory storage systems.

Key Differences

• Sensitivity:

  • Latches are level-sensitive (active when enabled).
  • Flip flops are edge-sensitive (active on clock edges).

• Operation:

  • Latches can change state as long as the enable signal is active.
  • Flip flops change state only at specific moments (clock edges).

• Usage:

  • Latches are often used in simpler applications where level sensitivity is acceptable.
  • Flip flops are preferred in synchronous circuits requiring precise timing control.

Flip Flops

• Bistable circuits capable of storing one of two states (0 or 1).
• Triggered by a clock input, which determines when state changes occur.

Types of Flip Flops

• SR Flip Flop:
  • Set (S) and Reset (R) inputs.
  • Sets the output to 1 when S is high, resets to 0 when R is high.
• JK Flip Flop:
  • Extension of SR flip flop.
  • Additional J and K inputs that allow for toggling between states (changing from 0 to 1 or vice-versa).
• D Flip Flop:
  • Single data input (D) and a clock signal.
  • Captures the value of the data input (D) on the rising or falling edge of the clock signal.
• T Flip Flop:
  • Single input T and a clock signal.
  • Toggles between states (0 to 1 or 1 to 0) on each positive clock edge when T is high.

Applications of Flip Flops

• Data storage (registers)
• Frequency dividers in digital circuits
• State machines in sequential logic

Latches

• Level-sensitive devices that store one bit of data.
• Remain in the same state as long as the enable signal is active.

Types of Latches

• SR Latch: Similar to SR flip flop but lacks a clock signal; state changes while inputs are active.
• D Latch: Captures the input value (D) when the enable signal is high.

Functionality of Latches

• Transparent operation when enabled - output follows the input.
• Output is held constant when the enable signal is low (deactivated).

Applications of Latches

• Temporary data storage
• Level-sensitive elements in memory systems.
• Building blocks for more complex memory storage systems.

Key Differences Between Latches and Flip Flops

• Sensitivity: Latches are level-sensitive, while flip flops are edge-sensitive.
  • Latches respond to the input value as long as the enable signal is active.
  • Flip flops respond to input only on a specific clock edge (rising or falling).
• Operation:
  • Latches change state while the enable signal is active.
  • Flip flops change state only at the clock edge.
• Usage:
  • Latches are more suitable for simpler applications where level sensitivity is acceptable.
  • Flip flops are preferred in synchronous circuits that demand precise timing control.