Trigger circuit structure and action characteristics

Probe domestic switch needle KG-300K, needle head diameter is 3.0mm, normally open switch needle

Industrial Router Crystal 3.2*2.5mm 3225 26M (26.000MHZ) 12PF 10PPM 20PPM 30PPM

Photocoupler

RS latches are fundamental building blocks in digital electronics, typically constructed using two NAND gates as shown in Figure 4.2.2(a). These latches have two active-low inputs: S (Set) and R (Reset), and a pair of complementary outputs Q and Q'. When Q is 1 and Q' is 0, the latch is in the set state; when Q is 0 and Q' is 1, it's in the reset state. There are four possible input combinations for S and R. If both inputs are invalid, the latch retains its previous state. If S is valid and R is invalid, the output becomes Q=1 and Q'=0. If R is valid and S is invalid, the output becomes Q=0 and Q'=1. However, if both S and R are valid at the same time, the latch enters an indeterminate state. This situation is problematic because it leads to unpredictable behavior.

How can this happen? It’s usually due to external interference or noise in the system. For example, if a negative pulse is applied to the S input, the latch sets to 1. A negative pulse means a signal that transitions from high to low and then back to high. Similarly, applying a negative pulse to the R input resets the latch to 0. But what happens if both pulses arrive simultaneously? This would be like trying to store both 1 and 0 at the same time, which is logically impossible. In practice, such a scenario may occur due to timing issues or electrical noise, causing the latch to behave unpredictably.

One practical application of RS latches is in anti-jitter circuits. Mechanical switches often produce contact bounce when activated, leading to multiple rapid transitions between 1 and 0. This can cause errors in digital systems. An RS latch helps stabilize the signal by ensuring that only one stable state is recognized, even if the switch bounces multiple times.

Another important use of latches is in synchronous circuits, where a clock signal (CP) controls when the inputs are processed. This ensures that the latch only updates its state when the clock is high, reducing the risk of interference and improving reliability. The CP signal also helps eliminate race conditions, where changes in input signals happen too quickly for the latch to process them correctly. By introducing a narrow clock pulse, the system can better handle unstable data inputs and avoid logical errors.

In addition to basic RS latches, D latches and master-slave flip-flops are commonly used in more complex digital designs. Master-slave flip-flops consist of two cascaded latches, with their clock signals being complementary. This design prevents the inputs from affecting the output until the clock signal changes, ensuring more stable and predictable behavior. These components are essential in modern digital systems, providing reliable storage and control of binary information.