Low noise oscillator having switching network
AssigneeAnalog Devices, Inc.
InventorHyman Shanan
Life of this patent
Estimating the term…
Abstract
Apparatus and methods are also disclosed related to an oscillator that includes a switching network configured to tune a resonant frequency of a resonant circuit. One such apparatus includes a switching network having a circuit element, such as a capacitor, that can be selectively coupled to the resonant circuit by a switch, such as a field effect transistor. For instance, the switch can electrically couple to circuit element to the resonant circuit when on and not electrically couple the circuit element to the resonant circuit when off. An active circuit can assert a high impedance on an intermediate node between the switch and the circuit element when the switch is off.
Claims24
An apparatus comprising:
- a resonant circuit having a first terminal and a second terminal, the resonant circuit including a switching network configured to tune a resonant frequency of the resonant circuit, the switching network including a first switching circuit comprising:
- a circuit element having at least a first end and a second end, the first end electrically coupled to the first terminal of the resonant circuit;
- a switch configured to electrically couple the second end of the circuit element to the second terminal when on and not to electrically couple the second end of the circuit element to the second terminal when off, the switch configured to turn on and to turn off responsive to a control signal;
- and
- an active circuit comprising a biasing element, the biasing element comprising at least one of a diode connected transistor or a diode, the biasing element configured to:
- apply a bias signal to an intermediate node between the switch and the second end of the circuit element, and assert a high impedance on the intermediate node when the switch is off, wherein the bias signal is a logical complement of the control signal.
An apparatus comprising:
- a resonant circuit having a non-inverted node and an inverted node, the resonant circuit having a switching network configured to tune a resonant frequency of the resonant circuit, the switching network comprising:
- a circuit element having at least a first end and a second end;
- a switch configured to couple to the second end of the circuit element to the inverted node when on and not to couple second end of the circuit element to the inverted node when off;
- and
- one or more other circuit elements comprising a biasing element, the biasing element comprising a diode connected transistor, the biasing element configured to generate a high impedance on an intermediate node between the switch and the second end of the circuit element when the switch is off, to apply a bias to the intermediate node when the switch is off to maintain the switch in an off position, and to cease generating the high impedance on the intermediate node when the switch is on, wherein the diode connected transistor and the switch are of opposite conductivity types.
A method of reducing phase noise in an oscillator, the method comprising:
- selectively coupling at least one circuit element to a node of a resonant circuit via activation of a switch in response to a signal applied to a control terminal of the switch for tuning of a frequency of the resonant circuit;
- generating, via a biasing element comprising at least one of a diode connected transistor or a diode, a high impedance on an intermediate node between the switch and the at least one circuit element when the switch is off to reduce phase noise of the oscillator;
- and
- applying, via the biasing element, a bias signal to the intermediate node to maintain the switch in the off position, wherein the bias signal is a logical complement of the signal applied to the control terminal of the switch.
Dependencies are inferred from the claim text.