Low noise oscillator
A low noise oscillator constructed using a rotary traveling wave oscillator. The conductors of the rotary traveling wave oscillator provide at any tap position a pair of oppositely phased oscillations and these oscillations have slightly different phases at positions that are slightly different on the conductors. Regeneration devices establish and maintain oscillations on the conductors of the traveling wave oscillator. A regeneration device made from p-channel and n-channel transistors is connected to the conductors of the traveling wave oscillator in such a way that the gate connections of the transistors receive the traveling wavefront before the drains of the transistors receive the wavefront. By the time the regeneration device switches in response to the wavefront arriving at the gates of the transistors, the wavefront has arrived at the drains. This creates little or no disturbance to the wave on the conductors and results in low phase noise.
1. A low noise oscillator comprising:
one or more transmission line segments, each segment having ends and a length of spaced apart first and second conductors therebetween, each length of conductor being electrically continuous;
an odd number of passive connection means coupling the ends of the one or more segments to form a closed loop of segments and the passive connection means; and
a plurality of regeneration devices located at various spaced-apart positions on the loop and connected between the first and second conductors of a segment,
wherein the regeneration devices are operative to establish and maintain on the loop a wave traveling around the loop, the traveling wave wave including a voltage wave between the first and second conductors, a single lap of the wave around the loop defining a propagation time, and
wherein each of the passive connection means causes the voltage of the traveling wave between the first and second conductors to reverse polarity, so that, at any location on a segment, there is a pair of oppositely phased oscillations having a period equal to twice the propagation time.
2. A low noise oscillator as recited in claim 1 ,
wherein the traveling wave travels in a particular direction around the loop; and
wherein each of the regeneration devices includes first and second inverting amplifiers, the first amplifier having an input connected at a tap position to the first conductor and an output connected at an output position to the second conductor, the second amplifier having an input connected at a tap position to the second conductor and an output connected at an output position to the first conductor, each amplifier having an associated delay time for responding to a change on its input,
wherein, for each amplifier, there is a physical offset between its output position and its tap position so that there is a time difference between the traveling wave arriving at the tap position and arriving at the output position, said time difference being approximately equal to the amplifier's associated delay time.
3. A low noise oscillator as recited in claim 2 , wherein the conductors of each transmission line segment are routed with a plurality of folds, each having a base at which the first and second inverting amplifiers are connected between the first and second conductors, each fold having a length that provides physical offset between the tap position and the output position.
4. A low noise oscillator as recited in claim 3 ,
wherein the conductors of each transmission line segment have inductance and resistance, and between the conductors conductance and capacitance that determine the propagation time of the traveling wave; and
wherein the inductance, resistance, capacitance, and conductance are separately or jointly adjusted to tune the time difference.
5. A low noise oscillator as recited in claim 2 , wherein for each inverting amplifier the tap position is altered to tune the physical offset to the associated delay time of the amplifier.
6. A low noise oscillator as recited in claim 2 , wherein the tap positions of each inverter inverting amplifier are offset by the same amount.
7. A low noise oscillator as recited in claim 1 , wherein the conductors of the transmission line segment are together routed with a plurality of folds so as to reduce the total space the oscillator occupies.
8. A low noise oscillator as recited in claim 1 ,
wherein the conductors of the transmission line segments are together routed with a plurality of folds and the passive connection means are crossovers; and
wherein each crossover is positioned to approximately balance coupling from an adjacent conductor that is parallel and in proximity to a conductor continuous through the crossover.
9. A low noise oscillator as recited in claim 1 ,
wherein the conductors of the transmission line segments are each routed with a plurality of folds and the passive connection means are crossovers; and
wherein folds of each of the conductors are offset from each other to increase the inductance of the segments.
10. A low noise oscillator as recited in claim 1 , wherein the inverting amplifiers are CMOS inverters.
11. A low noise oscillator as recited in claim 1 , wherein the inverting amplifiers are MOS inverters.
12. A low noise oscillator as recited in claim 1 , wherein the inverting amplifiers are bipolar inverters.
13. A low noise oscillator as recited in claim 1 , wherein the inverting amplifiers are biFET inverters.
14. A low noise oscillator as recited in claim 1 ,
wherein the inverting amplifiers are CMOS inverters, each having a pair of gate inputs connected, respectively, to a first and second tap position on a segment and an output connected to an output position,
wherein, for each gate input, each inverting amplifier has an associated delay time for responding to a change thereon; and
wherein, for each amplifier, there is a physical offset between each tap position and the output position, such that there is a time difference between the traveling wave arriving at each tap position and the traveling wave arriving at the output position, said time difference being approximately equal to the associated delay time.
15. A low noise oscillator as recited in claim 1 ,
wherein the traveling wave travels in a particular direction around the loop; and
wherein each of the regeneration devices includes a first inverter and a second inverter, the first and second inverters each including a p-channel and n-channel transistor, each transistor having a gate and a channel between a source and a drain node, the source node of each p-channel transistor being connected to a supply voltage node, the source node of each n-channel transistor being connected to a reference voltage node,
wherein the gates of the p-channel and n-channel of the first inverter are connected to the first conductor at first and second tap positions, respectively, and the drains are connected to the second conductor at a first output position,
wherein the gates of the p-channel and n-channel of the second inverter are connected to the second conductor at first and second tap positions, respectively, and the drains are connected to the first conductor at a second output position,
wherein for each gate, the inverter has an associated delay time for responding to a change thereon,
wherein, for each inverter, there is a physical offset between each tap position and the output position such that there is a time difference between the traveling wave arriving at each tap position and the traveling wave arriving at the output position, the time difference being approximately equal to the associated delay time of the inverter.
16. A low noise oscillator as recited in claim 15 , wherein, for each inverter, each tap position is altered to tune the physical offset to the associated delay time.
17. A low noise oscillator as recited in claim 15 , wherein, for each inverter, each tap position has the same physical offset.
18. A method for creating low phase noise oscillations, the method comprising:
establishing a traveling wave on a loop of one or more transmission line segments, wherein each segment has between its ends a length of spaced apart and electrically continuous first and second conductors and an odd number of passive connection means coupling the ends of the one or more segments to form a closed loop, the traveling wave including a voltage wave between the first and second conductors and being maintained by a plurality of regeneration devices connected between the conductors of the transmission line segments, each connection means for reversing the polarity of the voltage wave between the conductors, wherein each regeneration device includes back-to-back inverting amplifiers and each amplifier has an input and an output and a delay time for responding to a change on the input; and
causing a difference in time between the traveling wave arriving at the input of each amplifier and the traveling wave arriving at the output of each amplifier, said time difference being approximately equal to the amplifier's delay time.
19. A method for creating low phase noise oscillations as recited in claim 18 , wherein each transmission line segment has a plurality of folds.
20. A method for creating low phase noise oscillations as recited in claim 18 ,
wherein the inverting amplifiers are CMOS inverters, each having a pair of gate inputs connected, respectively, to a first and second tap position on a segment and an output connected to an output position,
wherein, for each gate input, each inverting amplifier has an associated delay time for responding to a change thereon;
wherein causing a difference in time includes
causing a first difference in time between the first tap position and the output position and
causing a second difference in time between the second tap position and the output position, said time differences between the first tap position and the output position and the second tap position and the output position being approximately equal to the associated delay times.