“Many analog circuits require a clock signal, or the ability to perform a task after a certain amount of time. For such applications, there are various suitable solutions. For simple timing tasks, standard 555 circuits can be used. Using the 555 circuit and appropriate external components, many different tasks can be performed.
Many analog circuits require a clock signal, or the ability to perform a task after a certain amount of time. For such applications, there are various suitable solutions. For simple timing tasks, standard 555 circuits can be used. Using the 555 circuit and appropriate external components, many different tasks can be performed.
However, the fairly widely used 555 timer has the disadvantage of being less precise in its settings. The 555 timer works by charging an external capacitor and detecting the voltage threshold. Such a circuit is easy to make, but its accuracy largely depends on the actual value of its capacitance.
Crystal oscillators are suitable for applications where high accuracy is required. They can be quite accurate, but they have one downside: reliability. Anyone involved in electrical equipment repair knows that failures are often caused by large electrolytic capacitors. Crystal oscillators are the second largest cause of failure.
A third way to measure the length of time or generate a clock signal is to use a simple small microcontroller. Of course, there are a large number of devices to choose from, and each can choose a different optimization method. However, these devices require programming, and the user requires a certain level of knowledge to use them; furthermore, due to their digital design, great care must be taken when used in critical applications. For example, if the microcontroller fails, the entire system will have problems.
In addition to these three basic clock-generation building blocks, there are other lesser-known alternatives. The TimerBlox module from Analog Devices is one such alternative. They are silicon-based timing blocks, and unlike microcontrollers, they are fully analog in operation and can be adjusted with resistors. Therefore, it does not require software programming, and the function is very reliable. Figure 1 provides an overview of the different TimerBlox modules and describes their respective basic functions. Countless other functions can be generated using these basic building blocks.
Figure 1. TimerBlox circuit used to generate various timing functions.
In contrast to the widely used 555 timer circuit, the TimerBlox circuit does not rely on external capacitors for charging. All settings are done in resistors, so its function is more precise. Accuracy can reach 1% to 2%. Crystal oscillators are about 100 times more accurate, but come with various disadvantages.
Figure 2. Envelope detector using the LTC6993 TimerBlox integrated circuit.
The applications of timing modules are very diverse. Analog Devices has released many example circuits. Figure 2 shows an envelope detector. Several fast pulses are combined to form a longer pulse. The external components of the LTC6993-2 are minimal for this application. The capacitor in the circuit is just a backup capacitor to support the supply voltage and has no effect on the accuracy of the timing module.
Other interesting applications include phase-shift synchronization of multiple switching regulators for power supplies, or adding spread spectrum modulation to switching regulator ICs with synchronized inputs. Another typical application is the deployment of specified delays, that is, timers that provide delayed start-up for specific circuit segments.
There are many different technical solutions for generating clock signals and performing various time-based tasks. Each option has its own advantages and disadvantages. For example, silicon oscillators such as TimerBlox modules have the characteristics of ease of use, high precision, and high reliability because they use variable resistors instead of capacitors.