How does a relaxation oscillator produce a periodic waveform without using LC components?
1 Answer
A relaxation oscillator is an electronic circuit that generates a periodic waveform without using LC (inductor-capacitor) components. Instead, it relies on the charging and discharging of capacitors and the threshold behavior of certain active elements like transistors or operational amplifiers (op-amps).
One common type of relaxation oscillator is the "astable multivibrator," which uses two capacitors and two transistors (or two op-amps) in a feedback loop. Here's a basic explanation of how it works:
Charging Phase: Initially, both capacitors are discharged. One transistor (or op-amp) acts as a charging switch, and the other transistor (or op-amp) acts as a discharging switch. The charging switch is turned on, allowing one of the capacitors to charge rapidly. The charging time is determined by the RC time constant, where R is the resistor connected in series with the capacitor and C is the capacitance.
Threshold Detection: While the first capacitor charges, the second capacitor discharges through the second transistor (or op-amp). As soon as the voltage on the second capacitor drops below a certain threshold voltage (determined by the voltage level required to switch the transistor or op-amp), the discharging switch changes state.
Discharging Phase: When the discharging switch changes state, it stops discharging the second capacitor, and instead, it starts charging the first capacitor, while the first capacitor starts discharging through the first switch. The cycle then repeats, with the two capacitors exchanging roles continuously.
The charging and discharging process continues indefinitely, leading to a periodic waveform at the output. The frequency of the oscillation depends on the values of the resistors and capacitors in the circuit.
An important point to note is that relaxation oscillators are not precise in their frequency, and the frequency stability can be affected by temperature variations and component tolerances. However, they are widely used in various applications, such as timers, pulse generators, and clock signal generation in simple digital circuits, where precision is not critical.
One common type of relaxation oscillator is the "astable multivibrator," which uses two capacitors and two transistors (or two op-amps) in a feedback loop. Here's a basic explanation of how it works:
Charging Phase: Initially, both capacitors are discharged. One transistor (or op-amp) acts as a charging switch, and the other transistor (or op-amp) acts as a discharging switch. The charging switch is turned on, allowing one of the capacitors to charge rapidly. The charging time is determined by the RC time constant, where R is the resistor connected in series with the capacitor and C is the capacitance.
Threshold Detection: While the first capacitor charges, the second capacitor discharges through the second transistor (or op-amp). As soon as the voltage on the second capacitor drops below a certain threshold voltage (determined by the voltage level required to switch the transistor or op-amp), the discharging switch changes state.
Discharging Phase: When the discharging switch changes state, it stops discharging the second capacitor, and instead, it starts charging the first capacitor, while the first capacitor starts discharging through the first switch. The cycle then repeats, with the two capacitors exchanging roles continuously.
The charging and discharging process continues indefinitely, leading to a periodic waveform at the output. The frequency of the oscillation depends on the values of the resistors and capacitors in the circuit.
An important point to note is that relaxation oscillators are not precise in their frequency, and the frequency stability can be affected by temperature variations and component tolerances. However, they are widely used in various applications, such as timers, pulse generators, and clock signal generation in simple digital circuits, where precision is not critical.