Quadrature LC Tank Digitally Controlled Ring Oscillator

Abstract

A quadrature LC tank based digitally controlled ring oscillator (DCO). The oscillator structure incorporates a plurality of stages, each stage including a buffer and a series LC tank. Four stages are coupled together to create a 360 degree phase shift around a loop. The oscillation frequency of the oscillator is the same as the resonant frequency of each LC tank, therefore it avoids quality factor degradation of LC tanks found in the prior art. In one example embodiment, class-D amplifiers are used to drive each of the LC tanks. Capacitor banks before at the input and output of the buffers provide coarse and fine tuning of the frequency of oscillation. The high efficiency exhibited by these amplifiers results in very good phase noise performance of this oscillator. The oscillator utilizes a startup circuit to launch oscillation upon power on.

1 - 43 . (canceled) 
     
     
         44 . A ring oscillator, comprising:
 a plurality of phase shifters configured in a loop, each phase shifter operative to generate a substantially 90-degree phase shift and to provide voltage amplification of its respective input;   a plurality of active circuits, each active circuit coupled to and associated with one of said phase shifters;   wherein said plurality of active circuits are dc-coupled to their respective phase shifters; and   wherein a gain of said plurality of active circuits combined with the voltage amplification of said phase shifters causes said loop to oscillate.   
     
     
         45 . The ring oscillator according to  claim 44 , wherein said phase shifters comprise one or more passive components. 
     
     
         46 . The ring oscillator according to  claim 45 , wherein said passive components comprise a series inductor and capacitor. 
     
     
         47 . The ring oscillator according to  claim 45 , wherein said one or more passive components comprises at least one transformer. 
     
     
         48 . The ring oscillator according to  claim 44 , wherein said active circuit comprises an inverter. 
     
     
         49 . The ring oscillator according to  claim 44 , wherein said active circuit comprises a nonlinear amplifier. 
     
     
         50 . The ring oscillator according to  claim 44 , wherein said active circuit comprises a voltage amplifier. 
     
     
         51 . The ring oscillator according to  claim 44 , further comprising a startup circuit operative to inject one or more pulses into said loop to launch said oscillation, said startup circuit turned off and disconnected after oscillation in said loop is established. 
     
     
         52 . The ring oscillator according to  claim 44 , further comprising a plurality of first tuning capacitors, each first tuning capacitor coupled to and associated with one of said active circuits and operative to provide relatively coarse frequency tuning control of said ring oscillator. 
     
     
         53 . The ring oscillator according to  claim 44 , further comprising a plurality of second tuning capacitors, each second tuning capacitor coupled to and associated with one of said active circuits and operative to provide relatively fine frequency tuning control of said ring oscillator. 
     
     
         54 . The ring oscillator according to  claim 44 , further comprising a starter circuit incorporating an auxiliary oscillator connected to a node in said loop for a finite period of time and operative to inject one or more pulses into said loop thereby generating an initial oscillation therein. 
     
     
         55 . The ring oscillator according to  claim 54 , wherein said startup circuit comprises back to back inverter pairs coupled to one or more nodes in said loop. 
     
     
         56 . A ring oscillator, comprising:
 a plurality of phase shifters configured in a loop, each phase shifter operative to generate a substantially 90-degree phase shift and to provide voltage amplification of its respective input;   a plurality of active circuits, each active circuit coupled to and associated with a respective one of said phase shifters;   wherein at least one of said plurality of phase shifters and said plurality of active circuits have single ended circuit structure; and   wherein a gain of said plurality of active circuits combined with the voltage amplification of said phase shifters enables said loop to oscillate.   
     
     
         57 . The ring oscillator according to  claim 56 , wherein said plurality of phase shifters comprise at least one of a series inductor and capacitor, one or more passive components, and at least one transformer. 
     
     
         58 . The ring oscillator according to  claim 56 , wherein said active circuits comprise at least one of an inverter, a nonlinear amplifier, and a voltage amplifier. 
     
     
         59 . The ring oscillator according to  claim 56 , further comprising a plurality of first tuning capacitors, each first tuning capacitor coupled to and associated with one of said active circuits and operative to provide relatively coarse frequency tuning control of said ring oscillator. 
     
     
         60 . The ring oscillator according to  claim 56 , further comprising a plurality of second tuning capacitors, each second tuning capacitor coupled to and associated with one of said active circuits and operative to provide relatively fine frequency tuning control of said ring oscillator. 
     
     
         61 . A ring oscillator, comprising:
 a plurality of phase shifters configured in a loop, each phase shifter operative to generate a substantially 90-degree phase shift and to provide voltage amplification of its respective input;   a plurality of active circuits wherein each active circuit consists of an inverter, each inverter coupled to and associated with a respective one of said phase shifters;   wherein said plurality of inverters are dc-coupled to their respective phase shifters; and   wherein a gain of said plurality of inverters combined with the voltage amplification of said phase shifters enables said loop to oscillate.   
     
     
         62 . The ring oscillator according to  claim 61 , wherein said plurality of phase shifters comprise at least one of a series inductor and capacitor, one or more passive components, and at least one transformer. 
     
     
         63 . The ring oscillator according to  claim 61 , further comprising a plurality of first tuning capacitors, each first tuning capacitor coupled to and associated with one of said active circuits and operative to provide relatively coarse frequency tuning control of said ring oscillator. 
     
     
         64 . The ring oscillator according to  claim 61 , further comprising a plurality of second tuning capacitors, each second tuning capacitor coupled to and associated with one of said active circuits and operative to provide relatively fine frequency tuning control of said ring oscillator.