Low power wide tuning range oscillator
A wide tuning range oscillator system uses multiple active cores with cross-coupled transistors and multiple tapped inductors having windings that can be connected to circuit nodes. These active cores are connected to a pair of symmetric tapping points and are switched ON/OFF by biasing elements. Biasing schemes and the topology of the individual cross-coupled cores may be different from each other. The tapping points are symmetrically arranged around the center point of the inductor. One or more of the active cores may be enabled for tuning the center frequency of the oscillator system.
1. An oscillator comprising:
a first oscillator core comprising:
a first pair of cross-coupled transistors including first and second transistors; and
a first variable resistor coupled to the first pair of cross-coupled transistors; and
a resonator tank comprising a capacitor and a tapping inductor, the tapping inductor having a first symmetrical pair of tapping nodes including first and second tapping nodes, the first tapping node coupled to the first transistor, the second tapping node coupled to the second transistor, the capacitor coupled between the first and second tapping nodes;
wherein the tapping inductor has differential symmetry and self biasing at a point of symmetry within the tapping inductor;
wherein when a first signal and a second signal, the first and second signal being opposite in phase, are applied to terminals of the oscillator, an effective AC swing at the point of symmetry is substantially zero.
2. The oscillator of claim 1 , wherein:
the first oscillator core further comprises:
a second pair of cross-coupled transistors including third and fourth transistors; and
a second variable resistor coupled to the second pair of cross-coupled transistors;
the first tapping node is coupled to the third transistor; and
the second tapping node is coupled to the fourth transistor.
3. The oscillator of claim 2 , wherein:
the first pair of cross-coupled transistors comprises p-type transistors; and
the second pair of cross-coupled transistors comprises n-type transistors.
4. The oscillator of claim 1 , wherein:
the oscillator further comprises a second oscillator core comprising:
a second pair of cross-coupled transistors including third and fourth transistors; and
a second variable resistor coupled to the second pair of cross-coupled transistors; and
the tapping inductor has a second symmetrical pair of tapping nodes including third and fourth tapping nodes, the third tapping node coupled to the third transistor, the fourth tapping node coupled to the fourth transistor.
5. The oscillator of claim 4 , wherein the oscillator further comprises:
a first switch coupled to the first variable resistor; and
a second switch coupled to the variable second resistor.
6. The oscillator of claim 4 , wherein:
the first oscillator core further comprises:
a third pair of cross-coupled transistors including fifth and sixth transistors; and
a third variable resistor coupled to the third pair of cross-coupled transistors;
the second oscillator core further comprises:
a fourth pair of cross-coupled transistors including seventh and eighth transistors; and
a fourth variable resistor coupled to the fourth pair of cross-coupled transistors;
the first tapping node is coupled to the fifth transistor;
the second tapping node is coupled to the sixth transistor;
the third tapping node is coupled to the seventh transistor; and
the fourth tapping node is coupled to the eighth transistor.
7. The oscillator of claim 1 , wherein the tapping inductor comprises a monolithic inductor.
8. The oscillator of claim 7 , wherein the tapping inductor comprises concentric ring segments electrically connected to form first and second coils, the concentric ring segments of the first coil interleaved with the concentric ring segments of the second coil.
9. An oscillator comprising:
a first oscillator core comprising:
a first pair of cross-coupled transistors including first and second transistors, the first transistor having a first source, a first gate, and a first drain, the second transistor having a second source, a second gate, and a second drain, wherein the first gate is coupled to the second drain and the second gate is coupled to the first drain; and
a first variable resistor coupled to the first and second sources; and
a resonator tank comprising a capacitor and a tapping inductor, the tapping inductor having a first symmetrical pair of tapping nodes including first and second tapping nodes, the first tapping node coupled to the first drain, the second tapping node coupled to the second drain, the capacitor coupled between the first and second tapping nodes;
wherein the tapping inductor has differential symmetry and self biasing at a point of symmetry within the tapping inductor;
wherein when a first signal and a second signal, the first and second signal being opposite in phase, are applied to terminals of the oscillator, an effective AC swing at the point of symmetry is substantially zero.
10. The oscillator of claim 9 , wherein:
the first oscillator core further comprises:
a second pair of cross-coupled transistors including third and fourth transistors, the third transistor having a third source, a third gate, and a third drain, the fourth transistor having a fourth source, a fourth gate, and a fourth drain, wherein the third gate is coupled to the fourth drain and the fourth gate is coupled to the third drain; and
a second variable resistor coupled to the third and fourth sources;
the first tapping node is coupled to the third drain; and
the second tapping node is coupled to the fourth drain.
11. The oscillator of claim 9 , wherein:
the oscillator further comprises a second oscillator core comprising:
a second pair of cross-coupled transistors including third and fourth transistors, the third transistor having a third source, a third gate, and a third drain, the fourth transistor having a fourth source, a fourth gate, and a fourth drain, wherein the third gate is coupled to the fourth drain and the fourth gate is coupled to the third drain; and
a second variable resistor coupled to the third and fourth sources; and
the tapping inductor has a second symmetrical pair of tapping nodes including third and fourth tapping nodes, the third tapping node coupled to the third drain, the fourth tapping node coupled to the fourth drain.
12. The oscillator of claim 11 , wherein the oscillator further comprises:
a first switch coupled to the first variable resistor; and
a second switch coupled to the second variable resistor.
13. The oscillator of claim 11 , wherein:
the first oscillator core further comprises:
a third pair of cross-coupled transistors including fifth and sixth transistors, the fifth transistor having a fifth source, a fifth gate, and a fifth drain, the sixth transistor having a sixth source, a sixth gate, and a sixth drain, wherein the fifth gate is coupled to the sixth drain and the sixth gate is coupled to the fifth drain; and
a third variable resistor coupled to the fifth and sixth sources;
the second oscillator core further comprises:
a fourth pair of cross-coupled transistors including seventh and eighth transistors, the seventh transistor having a seventh source, a seventh gate, and a seventh drain, the eighth transistor having an eighth source, an eighth gate, and an eighth drain, wherein the seventh gate is coupled to the eighth drain and the eighth gate is coupled to the seventh drain; and
a fourth variable resistor coupled to the seventh and eighth sources;
the first tapping node is coupled to the fifth drain;
the second tapping node is coupled to the sixth drain;
the third tapping node is coupled to the seventh drain; and
the fourth tapping node is coupled to the eighth drain.
14. The oscillator of claim 9 , wherein the tapping inductor comprises a monolithic inductor.
15. The oscillator of claim 14 , wherein the tapping inductor comprises concentric ring segments electrically connected to form first and second coils, the concentric ring segments of the first coil interleaved with the concentric ring segments of the second coil.