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The Magic of MOSFETs: How Does a Ring Oscillator Cleverly Use Delay to Generate Signals?
In the world of electronics, ring oscillators are known as ingenious and effective signal generators. This device consists of an odd number of NOT gates (or inverters) arranged in a ring structure, allowing the output signal to fluctuate back and forth between two voltage levels, representing the true sum in Boolean logic. Fake status. Since each inverter computes the logical NOT of its input, the final output of a string of odd-numbered inverters can be understood as the logical inverse of the first input.
The secret of the ring oscillator lies in its use of delay time, which allows the signal to be continuously generated in a loop.
When the first input is determined, the final output is confirmed after a limited period of time. Then, the final output is fed back to the first inverter to form a loop, eventually causing oscillation. It should be noted that if the total number of inverters is an even number, a ring oscillator cannot be formed because the final output will be consistent with the initial input.
The structure and operation of ring oscillators are not only important in digital circuits, they also serve as the basic building blocks of static random access memory (SRAM). Different ring oscillators can use a combination of inverting and non-inverting as needed, provided that the number of inverters must be an odd number, otherwise the system will not operate properly.
By design, ring oscillators only require a power supply to operate, and at certain voltages, oscillation can start spontaneously without reaching the MOSFET threshold voltage. At this time, the oscillation frequency of the ring oscillator can be improved through two methods: first, reducing the number of inverters can lead to a higher oscillation frequency while maintaining the same power consumption; second, increasing the power supply voltage can reduce the number of delay of the inverter, thereby increasing the oscillation frequency and increasing the input current consumption.
The oscillation period of the ring oscillator conveys an endless signal. As the inverter advances, time becomes an important element in signal generation.
For how ring oscillators operate, it is crucial to understand the concept of gate delay. In physical devices, the switching of any gate is not instantaneous. In the case of devices made with MOSFETs, the capacitance of the gate must be charged in order for current to flow between the source and bank. Therefore, the output of each inverter takes some time to change after its input changes. This situation means that if the number of inverters in the chain increases, the total gate delay also increases, thus reducing the oscillation frequency.
The principle of this ring oscillator comes from the time delay oscillator. The oscillator consists of an inverting amplifier and a delay element, forming a closed loop between the two. When the amplifier's input and output voltages are briefly stable, any small noise may cause a slight rise in the output voltage. After passing through the delay element, this small voltage change is again passed back to the amplifier input and is therefore further amplified and inverted.
Through this sequence of cycles, a square wave signal will eventually be generated, which is the magic of the ring oscillator.
The ring oscillator's oscillation waveform will eventually stabilize around the amplifier's output, becoming increasingly square as time goes by. However, the specific wave shape will change depending on the amplifier's limitations.
Once we further analyze the operation of the ring oscillator, it can be viewed as a decentralized time-delay oscillator. Each of its inverters jointly provides a signal delay effect in the ring structure. Every time a pair of inverters is added, the overall delay will increase accordingly, causing the oscillation frequency to decrease. Changes in the supply voltage will affect the delay of a single inverter. As the voltage increases, the delay usually decreases and the oscillation frequency increases.
In practical applications of ring oscillators, due to the jitter phenomenon they occur, they are often used in hardware random number generators. Ring oscillators will also be used to demonstrate new hardware technologies, much like the "Hello World" program demonstrates software technologies. In wafer testing, ring oscillators are used as part of the llds test structure to help people measure the impact of manufacturing process changes on performance.
By understanding this small structure in the electronic world, we can delve deeper into the mysteries of modern circuit design and how these technologies affect the devices we use in our daily lives. So, what will the future of electronic technology be like? What about further evolution?
