1. Field of the Invention
The present invention relates to a differential oscillator circuit and a method of starting up such a circuit.
2. Description of the Related Art
Differential oscillator circuits, such as that illustrated in FIG. 1 of the accompanying drawings, have been proposed for use in devices such as mobile telephones.
The circuit is symmetric about an oscillator 2 so as to provide a bias voltage to either side of the oscillator 2. A bias control line 4 is operable to turn the circuit on and off. In particular, the two halves of the bias circuitry are connected by a common line 6 which is operative to turn on the bias to both sides of the oscillator 2.
Once the bias has been applied to the oscillator 2, any noise in the circuit will start oscillation of the oscillator 2 and then oscillations will build up to the required steady-state.
U.S. Pat. No. 5,982,246 proposes a fast start-up oscillator. However, this does not have the advantages of a differential oscillator and, furthermore, relies upon pre-stressing a piezoelectric resonator with a DC bias voltage.