Astables (A-level only) Flashcards – AQA A-level Physics (7408)

What characterises the output states of an astable oscillator?

It has no stable output state: it repeatedly switches between two levels without a trigger for each transition.

What kind of signal does an astable oscillator produce, and what can it provide for a circuit?

A continuous train of pulses that can provide a clock signal.

How does an RC network control when an astable oscillator switches?

The capacitor charges and discharges through resistance. The resulting voltage changes determine when the oscillator switches.

For a fixed circuit arrangement, how do resistance and capacitance affect an RC-controlled astable oscillator’s frequency?

Increasing either generally lengthens the cycle and lowers frequency; decreasing either generally raises it. The exact relationship depends on the circuit.

What is the period $T$ of a clock signal?

The time for one complete cycle.

What is clock frequency $f$, and how is it related to the period $T$?

The number of cycles per second; $f = 1/T$.

What is the pulse width of a clock signal?

The duration of the pulse within one cycle.

For a clock signal whose pulse is high, what are the mark and space times?

Mark time: the high-level interval. Space time: the low-level interval.

How is the period of a clock signal related to its mark and space times?

The period is the sum of the mark and space times.

What is the duty cycle of a clock signal?

The fraction of the period occupied by the mark: $\text{duty cycle} = \frac{\text{mark time}}{T}$. It is often expressed as a percentage.

What does the mark-to-space ratio compare?

The mark time with the space time, rather than with the whole period.