LC-tuned voltage controlled ring oscillator
AssigneeNational Semiconductor Corporation
InventorRichard R. Rasmussen
Life of this patent
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Abstract
A differential delay stage for a ring oscillator utilizes a resonant circuit formed by an inductor and a capacitor consisting of two varactor diodes connected back-to-back. A common cathode connection is connected to a variable voltage source to vary the capacitance of the diodes. Other forms of capacitors may replace the varactor diodes. Varying the capacitance value varies the resulting oscillation frequency of the ring oscillator. When several delay stages, each incorporating the resonant circuit, are connected together in a ring, the net effect is to allow only a signal at the resonant frequency of the resonant circuits to propagate around the ring. Other oscillator circuits employing a resonant circuit are disclosed.
Claims12
A ring oscillator comprising a plurality of inverters connected in series as a ring, each of said inverters comprising:
- a differential amplifier having
- a first input terminal and a second input terminal for receiving input signals having opposite states,
- a first output terminal and a second output terminal for providing output signals of said differential amplifier having opposite states,
- a first current source providing current to a first node,
- a first transistor having a first current handling terminal connected to said first node and having its control terminal connected to said first input terminal,
- a second transistor having a first current handling terminal coupled to said first node and having its control terminal coupled to said second input terminal,
- wherein a second current handling terminal of said first transistor is connected to said first output terminal, and a second current handling terminal of said second transistor is connected to said second output terminal;
- and
- a resonant circuit connected between said first output terminal and said second output terminal, said resonant circuit having its highest impedance at a resonant frequency of said resonant circuit, whereby said resonant circuit causes said ring oscillator to oscillate at approximately said resonant frequency of said resonant circuit.
Dependencies are inferred from the claim text.