Johnson Herring Counter

Sıralı Mantık Devreleri
Sıralı Mantık DevreleriShift RegisterT-tipi Flip Flop
JK Flip FlopJohnson Ring SayıcıD-tipi Flip Flop
MultivibratörlerFlip-Flop Dönüşümleri

In today's article, we will discuss the Johnson Ring Counter. That's why it has a very important place in itself. Then let's get started.

If we apply a serial data signal for a SISO Shift Register, we have seen in our past articles that the latest Flip-Flopwill have the same data sequence on its release.

This serial data movement occurs through a resistance during a predetermined number of clock cycles. Thus, SISO allows the register to act as a kind of time delay circuit to the original input data signal.

But if we connect this shift register output back to its input, then the output data QD coming out of the last flip-flop will be the input data of qa, the first flip-flop. Next, we will have a closed loop circuit that "recirculates" the same data bit around a continuous loop for each state of its array, and this is the main process of a ring counter.

We can then convert a standard shift register circuit to a ring counter by returning the output to the input (feedback). It can also be more easily understood from the following circuit:

4-Bit Ring Counter

johnson herring counter
4-Bit Ring Counter

The example of the synchronous ring counter above is preset so that exactly one data bit in the register is set to the logic "1" and all other bits are reset to "0". A signal is applied to all Flip-Flops before they can reset their output to "logic" 0 "level". A " preset " pulse is then applied to the input of the first Flip-Flop (FFA) before the clock pulses are applied. This then places the logic "1" value in the circuit of the ring counter.

Thus, with each consecutive clock pulse, the counter repeatedly circulates the same data bit between four flip-flops around the "ring" each fourth hour cycle. However, to rotate the data correctly around the counter, the counter must first have an appropriate data pattern. Because all logic "0" or all logic "1" that appears in each clock cycle will override the ring counter.

Rotational Movement of a Ring Counter

johnson herring counter
Rotational Movement of a Ring Counter
johnson herring counter

The ring counter example shown above has four different situations. For this reason, it is also known as a "modulo-4" or "mod-4" counter, where each flip-flop output has a frequency value equal to a quarter or a quarter (1/4) of the main clock frequency.

The "MODULO" or "module" of a counter is the number of states in which the counter counts or sorts before repeating itself. A ring counter can be made to remove any modulo number. A "mod-n" ring counter requires a number of flip-flops connected to each other to circulate a single data bit that provides different output states of "n".

For example, the mod-8 ring counter requires eight flip-flops, and the mod-16 ring counter requires sixteen flip-flops.

Johnson Herring Counter

The Johnson ring counter, or "bent ring counters," is another shift register with exactly the same feedback as the standard ring counter above, but this time the output of the inverted Q of the latest flip flop is connected back to the D input of the first flip flop, as shown below.

The main advantage of this type of ring counter is that it only needs half a number of flip flops compared to the standard ring counter. Then the module number is halved. Therefore, a" n-stage "Johnson counter" circulates a single data bit that gives 2n different state sequences, and therefore can be considered a "mod-2n counter ".

4-bit Johnson Ring Counter

johnson herring counter
4-bit Johnson Ring Counter

This inversion of Q before feeding back to the D input causes the counter to be counted differently. Instead of counting from a fixed set of patterns, such as a 4-bit counter, it repeats so that it repeats like "0001"(1), "0010"(2), "0100"(4), "1000"(8). Johnson counter, first logic "1", Counts up and down as the previous logic passes right instead of "0". A 4-bit Johnson ring counter passes blocks of four logic "0" and then four logic "1", thereby producing an 8-bit pattern. This 8-bit pattern is repeated continuously when the inverted Q output is connected to input d.

4-Bit Johnson Herring Counter Accuracy Table

johnson herring counter
Truth table

In addition to counting or rotating data around a continuous loop, ring counters are used to detect various patterns or number values in a dataset. By connecting simple logic doors, such as AND or OR doors, to flip-flops outlets, the circuit can be made to determine a specific number or value.

Standard 2, 3 or 4 stage Johnson Ring counters can also be used to divide the frequency of the clock signal by changing the feedback connections.

For example, a 3-stage Johnson ring counter can be connected to data outputs in A, B and NOT-B and used as a 3-phase, 120-degree phase shift Square Wave generator. The standard 5-stage Johnson counter, such as the widely available CD4017, is often used as a synchronous decade counter/divider circuit.

Other combinations, such as the "quadruple" (sine/cosine) oscillator or the smaller 2-stage circuit, also called generator, can be used to produce four separate outputs, each 90 degrees "out of phase", to produce a 4-phase timing signal, as shown below.

2-Bit Quad Generator

johnson herring counter
2-bit quad Generator
johnson herring counter

Since four outputs from A to D are shifted 90 degrees relative to each other, a 2-phase full-step stepper motor can be driven for position control. In addition, they can be used with additional circuitry for the ability to rotate the engine to a specific position, as shown below.

StepPer Motor Control

johnson herring counter
2-phase (unipolar) full-step stepper motor