Oscillators are used everywhere in electronic circuitry mainly to generate a reference frequency or time period. Examples are carrier generation in a radio and clock generation in digital circuitry. They are also used for downconversion of signals in a radio, in voltage to frequency converters(a signal is much less susceptible to noise when it is in the form of frequency than in the form of voltage). There is a variety of architectures: “Relaxation” type-as the one above, ring oscillators, LC tank based oscillators, and oscillators based on other resonator types(e.g. quartz). The architecture chosen depends on desired purity(how close it is to an impulse in the frequency domain, or a perfectly periodic waveform in the time domain), stability, tunability etc.